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Heat Transfer

1996;():V004T09A001. doi:10.1115/96-GT-138.
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Encapsulated thermochromic liquid crystal (TLC) can be used to measure the surface temperature of stationary or rotating bodies. However, some research workers have reported a “rotational shift”; when the temperature of a rotating body is measured by thermocouples and TLC, there is a difference between the two sets of temperatures, and this difference increases with increasing rotational speed.

Two research groups (Camci and Glezer in the USA, and Owen, Pilbrow and Syson in the UK) have independently examined the effect of speed on TLC applied to the surfaces of rotating disks. The USA group used narrow-band TLC on a disk of 305-mm diameter rotating up to 7500 rev/min, measuring the surface temperature using an infra-red (IR) sensor. The UK group used wide-band TLC on a disk of 580-mm diameter rotating up to 7000 rev/min, measuring the temperature with an IR thermal imager. Both groups used the so-called hue technique to evaluate the temperature of the TLC and concluded that, even for centripetal accelerations in excess of 104g, there is no significant effect of rotational speed on either narrow-band or wide-band TLC. It is suggested that the “rotational shift” observed by some researchers was probably caused by thermal-disturbance errors, which affected the thermocouples, rather than by changes in the TLC.

Topics: Liquid crystals
Commentary by Dr. Valentin Fuster
1996;():V004T09A002. doi:10.1115/96-GT-150.
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High process efficiencies and high power-weight ratios are two major requirements for the economic operation of present day gas turbines. This development leads to extremely high turbine inlet temperatures and adjusted pressure ratios. The permissible hot gas temperature is limited by the material temperature of the blade. Intensive cooling is required to guarantee an economically acceptable life of the components which are in contact with the hot gas. Although film-cooling has been successfully in use for a couple of years along the suction side and pressure side, problems occur in the vicinity of the stagnation point due to high stagnation pressures and opposed momentum fluxes. In this area basic investigations are necessary to achieve a reliable design of the cooled blade.

In the present calculations, a code for the coupled simulation of fluid flow and heat transfer in solid bodies is employed. The numerical scheme works on the basis of an implicit finite volume method combined with a multi-block technique. The full, compressible 3-D Navier-Stokes equations are solved within the fluid region and the Fourier equation for beat conduction is solved within the solid body region. An elliptic grid generator is used for the generation of the structured computational grid, which is a combination of various C-type and H-type grids.

Results of a 3-D numerical simulation of the flow through a turbine blade cascade with and without cooling ejection at the leading edge through two slots are presented. The results are compared with 2-D numerical simulations and experimental results. It is shown that the distribution of the coolant on the blade surface is influenced by secondary flow phenomena which can not be taken into account by the 2-D simulations. Further coupled simulations with non-adiabatic walls in the leading edge region are performed with realistic temperature ratios and compared to the same case with adiabatic walls. It is shown that in the case of non-adiabatic walls the temperature on the blade wall is significantly lower than in the case of adiabatic walls.

Commentary by Dr. Valentin Fuster
1996;():V004T09A003. doi:10.1115/96-GT-161.
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The objective of the present work is the experimental investigation of the effects of rotation on the heat transfer due to a single row of circular jets impinging on a curved surface, relevant to turbine blade cooling. The local transfer coefficients were determined by means of the naphthalene sublimation technique using the analogy between heat and mass transfer. Spanwise average transfer coefficients were deduced from the local measurements and are discussed relative to the transfer in a nonrotating system. Results are presented for different stagger angles, jet Reynolds numbers and geometry parameters. The geometry parameters that were varied included the spacing between adjacent jet holes and the distance between the jet hole plate and the impingement surface. It is found that rotation does not improve heat transfer but can reduce it significantly, up to 40% below the transfer coefficient in a nonrotating system. Therefore, the effects of rotation have to be accounted for accurate predictions of the cooling pattern generated by impinging jets.

Commentary by Dr. Valentin Fuster
1996;():V004T09A004. doi:10.1115/96-GT-162.
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Most research involving arrays of impinging jets was conducted using steady state techniques which allow the impingement plate (through which the gas flows) to achieve an equilibrium (adiabatic) temperature during the test. Invariably, the impingement plate temperature was not reported for these tests as the floating temperature condition was taken to be representative of conditions in the application being modeled. Thermal analysis of gas turbine conditions showed the present authors that conditions in the engine could often be significantly different from this floating plate temperature state. Such conditions include engine operating point transients and situations in which the plate is fixed to the aerofoil in such a way to achieve good thermal contact. Furthermore, the capacity of the impingement plate to contribute to enhanced heat transfer by paying attention to the thermal boundary conditions at its support has not been realized. The influence of the impingement plate temperature on local target surface heat transfer was fully quantified by Van Treuren et al. (1993, 1994 and 1996), using a transient liquid crystal heat transfer technique. Superposition was used to show that the target surface heat flux can be written as the summation af two separate heat transfer coefficients. These temperature difference products quantify the contributions of the impingement plate and the target surface thermal boundary conditions. In other words:Display Formula

(1)
q=hjTw-Tj+hpTw-Tp
Van Treuren et al.’s experiments showed the heat transfer coefficient for target surface heat flux and impingement plate to target surface temperature difference, hp, can be up to 40% of the heat transfer coefficient for plenum to target surface temperature difference, hj, in crossflow areas away from the jet stagnation zone. The present report covers steady state experiments conducted at three average jet Reynolds numbers (10,000, 14,000, and 18,000) and two impingement to target plate spacings (1 and 4) for an inline array of jets. The purpose of the experiments was to determine the adiabatic impingement plate temperature expressed as a non-dimensional temperature difference, θ. The data allow the difference in thermal boundary conditions between the steady state experiments and the transient heat transfer experiments to be accounted for.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
1996;():V004T09A005. doi:10.1115/96-GT-163.
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Recent work, Van Treuren et al. (1993, 1994), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline and staggered array of impinging jets was tested over a range of average jet Reynolds numbers (10,000–40,000) for three impingement plate to target plate separations (1, 2 and 4). The array was confined on three sides and spent flow was allowed to exit in one direction. Local and average values are presented. These values for the two array configurations are then compared with each other as well as with previously published data in related geometries. A new correlation technique is presented, based on the local data, which breaks the target surface into jet and crossflow areas of interest, with excellent results. The correlation uses the local jet Reynolds number and local jet-to-crossflow mass velocity ratio. This new technique compared favourably with published correlations. Also presented is the influence of the impingement plate on the target plate heat transfer in the form of an effectiveness parameter. This influence is accounted for in the correlation.

Commentary by Dr. Valentin Fuster
1996;():V004T09A006. doi:10.1115/96-GT-167.
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The velocity profiles and turbulence characteristics are measured for a row of square jets inclined at 30° to the streamwise direction. The jet spacing-to-width ratio is 3.0 and no temperature (density) difference between the jets and the crossflow is introduced. Measurements are made using a three-component LDV system operating in coincidence mode which provides three components of velocity and all six turbulent Reynolds stresses at each location. Jet-to-crossflow velocity ratios (blowing ratios) of 1.5. 1.0, and 0.5 are used and the jet Reynolds number is fixed at about 5000 for all velocity ratios. The results are compared with previous data from normal jets at the same blowing ratios so that the influence of inclination on vortex formation can be shown. Calculations are carried out for all cases using a non-orthogonal finite volume computer code with the k-ε turbulence model. It is shown that the flow field at the jet exit is strongly influenced by the crossflow as well as by the inlet conditions at the entrance to the jet orifice. Therefore it is very useful to extend the computational domain into the plenum. Computational results compared with experimental results for a velocity ratio of 0.5 agree reasonably well. Some under-prediction of the streamwise flow velocity is observed. The computed turbulence kinetic energy values also drop below the experimental values downstream and near the wall. Agreement is not as good for the higher velocity ratios, particularly for the turbulence kinetic energy. Strong non-isotropy of the turbulence field can be observed from the experimental data.

Topics: Jets
Commentary by Dr. Valentin Fuster
1996;():V004T09A007. doi:10.1115/96-GT-169.
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This paper presents heat transfer measurements on a turbine airfoil in a linear cascade at various exit Reynolds and Mach numbers ranging from 3.2e5 to 1.6e6 and 0.2 to 0.8, respectively, which have been conducted with the transient liquid crystal technique. Two series were performed at turbulence intensities of 5.5% and 10%, the latter being created by a squared-bar mesh placed 10 meshsizes upstream of the turbine airfoils. While normally polished liquid crystals were used additional experiments were done at the high turbulence intensity with naturally rough liquid crystals.

All measurements indicate a gradual increase in heat transfer and an upstream shift of the laminar-to-turbulent transition with increasing Reynolds number and turbulence intensity. The leading edge heat transfer agrees well with correlations if the turbulence length scale is taken into account. The measurements conducted with rough liquid crystals show an earlier transition on the suction side. Calculations with a two-dimensional boundary layer code agree well with the measurements.

Commentary by Dr. Valentin Fuster
1996;():V004T09A008. doi:10.1115/96-GT-172.
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The external heat transfer coefficients, necessary for efficient and accurate turbine blade design, have been quantified using three independent methods of data reduction for the high-pressure turbine blades tested in a core engine. Two of the methods utilized external and internal thermocouple data to determine the heat transfer coefficient levels while the third method required the applied heat-flux levels to determine the coefficients. The heat-flux was calculated from the measured potential difference between thermocouple pairs embedded in the external and internal walls of the turbine blades. The instrumented airfoils were calibrated in a laboratory prior to engine testing. The results of the experimental test showed external heat transfer coefficients could be obtained in an engine environment with a ±3.2% minimum absolute uncertainty. All three data reduction methods produced external heat transfer coefficients within a high degree of accuracy and precision for all data locations on the instrumented airfoils. The three data reduction approaches are presented as well as the data for a specific location on a turbine blade for each method of data reduction. In addition, pre-test calibration procedures and data are discussed along with supporting engine instrumentation used to verify the data acquired during the experimental evaluation.

Commentary by Dr. Valentin Fuster
1996;():V004T09A009. doi:10.1115/96-GT-173.
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The present work is concerned with the flow reversal phenomenon that is caused by the centrifugal buoyancy forces in the case of three-dimensional radially outward flow through rectangular ducts rotating in orthogonal mode. Due to the flow reversal, regions of zero to low fluid velocity (stagnation) are created near the leading wall and the heat transfer, consequently, is impaired causing concerns for the design engineers. Three duct cross-sections of the same hydraulic diameter but different aspect ratios (1:1, 2:1 and 3.33:1) have been examined in this numerical study for flows at different rotation numbers and different temperature ratios. The rotation number examined ranged from 0.08 to 0.35. For each rotation number the temperature ratio is increased until the flow reversal phenomenon is observed in the CFD predictions. For all the three ducts, computations have been carried out for Reynolds number equal to 80,000. The onset of the flow reversal near the leading wall and at the exit of the single-pass flow passage is studied with the buoyancy number variation.

As the aspect ratio is increased while keeping the duct hydraulic diameter fixed, the buoyancy number required to cause the onset of flow reversal decreases. Also, for each of the three ducts examined it has been found that the buoyancy number required for the predicted reverse flow to occur increases as the rotation number is increased.

Commentary by Dr. Valentin Fuster
1996;():V004T09A010. doi:10.1115/96-GT-174.
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One viable option to improve cooling methods used for gas turbine blades is to optimize the geometry of the film-cooling hole. To optimize that geometry, effects of the hole geometry on the complex jet-in-crossflow interaction need to be understood. This paper presents a comparison of detailed flowfield measurements for three different single, scaled-up, hole geometries all at a blowing ratio and density ratio of unity. The hole geometries include a round hole, a hole with a laterally expanded exit, and a hole with a forward-laterally expanded exit. In addition to the flowfield measurements for expanded cooling hole geometries being unique to the literature, the testing facility used for these measurements was also unique in that both the external mainstream Mach number (Ma = 0.25) and internal coolant supply Mach number (Mac = 0.3) were nearly matched.

Results show that by expanding the exit of the cooling holes, the penetration of the cooling jet as well as the intense shear regions are significantly reduced relative to a round hole. Although the peak turbulence levels for all three hole geometries was nominally the same, the source of that turbulence was different. The peak turbulence level for both expanded holes was located at the exit of the cooling hole resulting from the expansion angle being too large. The peak turbulence level for the round hole was located downstream of the hole exit where the velocity gradients were very large.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
1996;():V004T09A011. doi:10.1115/96-GT-175.
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This study investigated a practical but never exploited issue concerning the influence of flow leakage through a gap downstream on the film cooling performance with a row of discrete-hole injection. A heat transfer system as such can be categorized as either a three-temperature or a four-temperature problem, depending on the direction of leakage through the gap. To fully characterize a three-temperature based film-cooling system requires knowledge of both local film effectiveness and heat transfer coefficient. A second film effectiveness is necessary for characterizing a four-temperature problem. All these variables can be experimentally determined, based on the transient method of thermochromic liquid crystal imaging. Although the overall convective transport in the region is expected to be dependent on the blowing ratios of the coolants, the mass flow ratio of the two injectants, and the geometry, the current results indicated that the extent of flow injection or extraction through the gap has significant effects on the film effectiveness and less on the heat transfer coefficient which is primarily dominated by the geometric disturbance of gap presence.

Topics: Leakage , Film cooling
Commentary by Dr. Valentin Fuster
1996;():V004T09A012. doi:10.1115/96-GT-176.
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The effect of varying coolant density on film cooling effectiveness for a turbine blade-model was numerically investigated and compared with experimental data. This model had a semi-circular leading edge with four rows of laterally-inclined film cooling orifices positioned symmetrically about the stagnation line. A curvilinear coordinate-based CFD code was developed and used for the numerical investigation. The code used a domain segmentation strategy in conjunction with general curvilinear grids to model the complex blade configuration. A multigrid method was used to accelerate the convergence rate. The time-averaged, variable-density, Navier-Stokes equations together with the energy or scalar equation were solved. Turbulence closure was attained by the standard k–ε model with a near-wall k model. Either air or CO2 was used as coolant in three cases of injection through single rows and alternatively staggered double raws of holes. Two different blowing rates were investigated in each case and compared with experimental data. The experimental results were obtained using a wind tunnel model, and the mass/heat analogy was used to determine the film cooling effectiveness. The higher density of the carbon dioxide coolant (approximately 1.5 times the density of air) in the isothermal mass injection experiments, was used to simulate the effects of injection of a colder air in the corresponding adiabatic heat transfer situation. Good agreement between calculated and measured film cooling effectiveness was found for low blowing ratio M ≤ 0.5 and the effect of density was not significant. At higher blowing ratio M > 1 the calculations consistently overpredict the measured values of film cooling effectiveness.

Commentary by Dr. Valentin Fuster
1996;():V004T09A013. doi:10.1115/96-GT-178.
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The paper presents a computer code for steady and unsteady, three-dimensional, compressible, turbulent, viscous flow simulations. The mathematical model is based on the Favre-averaged Navier-Stokes conservation equations, closed by a statistical model of turbulence. Turbulence effects are represented by using a low Reynolds number K-ω model. The numerical model makes use of a finite difference approximation in generalized coordinates for space discretization. The solution of time-dependent, three-dimensional, non-homogeneous, partial differential equations is obtained by solving, in a prescribed, symmetric pattern, three time-dependent, one-dimensional, homogeneous partial differential equations, representing convection and diffusion along each generalized coordinate direction, and one ordinary differential equation, representing generation and destruction. An explicit, multi-step, dissipative, Runge-Kutta scheme is finally adopted for time discretization.

The code is applied to simulate the flow through a linear cascade of turbine rotor blades, where detailed experimental data are available. Blade aerodynamic and heat transfer are computed, at variable Reynolds and Mach numbers and turbulence levels, and compared with experimental data. While the aerodynamic prediction is relatively unaffected by the properties of both mathematical and numerical models, the heat transfer prediction proves to be extremely sensitive to models details. Low Reynolds number K-ω turbulence models theoretically reproduce laminar, turbulent and transitional boundary layers. However, their practical use in a Navier-Stokes code does not allow to entirely capture the effects of turbulence intensity and Mach and Reynolds numbers on blade heat transfer.

Commentary by Dr. Valentin Fuster
1996;():V004T09A014. doi:10.1115/96-GT-180.
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Turbine blade endwall heat transfer measurements are given for a range of Reynolds and Mach numbers. Data were obtained for Reynolds numbers based on inlet conditions of 0.5 and 1.0 × 106, for isentropic exit Mach numbers of 1.0 and 1.3, and for freestream turbulence intensities of 0.25% and 7.0%. Tests were conducted in a linear cascade at the NASA Lewis Transonic Turbine Blade Cascade Facility. The test article was a turbine rotor with 136° of turning and an axial chord of 12.7 cm. The large scale allowed for very detailed measurements of both flow field and surface phenomena. The intent of the work is to provide benchmark quality data for CFD code and model verification. The flow field in the cascade is highly three-dimensional as a result of thick boundary layers at the test section inlet. Endwall heat transfer data were obtained using a steady-state liquid crystal technique.

Commentary by Dr. Valentin Fuster
1996;():V004T09A015. doi:10.1115/96-GT-181.
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Development of an adequate air cooling system for the thermally highly loaded leading edge and tip of the blade, that is cost effective and also relatively insensitive to manufacturing tolerances and operating environment continues to be one of the major challenges in advanced gas turbine design. Extensive studies on the convective (including impingement) and film cooling techniques produced remarkable progress in achieving a high cooling effectiveness level for turbine airfoils. However, in the case of turbine blades, application of these techniques has severe limitations. Highly effective impingement cooling needs to be combined with film discharge of the spent air to avoid a negative impact of crossflow on internal heat transfer and also provide additional thermal protection of the surface downstream of the discharge holes. Noticeable aerodynamic penalties, stress concentration and significant increase in manufacturing cost limit application of blade film cooling, particularly for moderately high operating temperatures.

Search for a highly effective robust design of internal airfoil cooling which can delay the use of film cooling resulted in the creation of a new technique which is described in this paper. This technique is based on generation of a swirling flow structure in the blade internal leading edge passage. Significant heat transfer augmentation can be achieved when the cooling air is delivered into the leading edge plenum tangentially to the inner concave surface. The best results can be obtained when the swirling flow is allowed to move radially, creating a three-dimensional screw-shaped flow in the plenum.

The presented results of the flow and heat transfer studies performed for the practical range of Reynolds numbers for the internal flow show that the leading edge screw-shaped cooling technique provides internal heat transfer rate comparable with impingement coupled with film discharge of the spent air, is more effective than impingement with cross flow and is almost five times higher than heat transfer in the smooth channel.

Topics: Cooling , Blades
Commentary by Dr. Valentin Fuster
1996;():V004T09A016. doi:10.1115/96-GT-187.
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The physics of the film cooling process for shaped, inclined slot–jets with realistic slot–length–to–width ratios (L/s) is studied for a range of blowing ratio (M) and density ratio (DR) parameters typical of gas turbine operations. The effect of inlet and exit shaping of the slot–jet on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. A previously documented computational methodology was applied for the study of four distinct configurations: (1) slot with straight edges and sharp comers (reference case); (2) slot with shaped inlet region; (3) slot with shaped exit region; and (4) slot with both shaped inlet and exit regions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness (η) and heat transfer coefficient (h) are presented. It is demonstrated that both η and h results are vital in the proper assessment of film cooling performance. The key parameters M and DR were varied from 1.0 to 2.0 and 1.5 to 2.0, respectively, to show their influence. Simulations were repeated for slot length–to–width ratio (L/s) of 3.0 and 4.5 in order to explain the effects of this important parameter. The computational simulations showed exceptionally strong internal consistency. Moreover, the ability of using a state–of–the–art computational methodology to sort the relative performance of different slot–jet film cooling configurations was clearly established.

Commentary by Dr. Valentin Fuster
1996;():V004T09A017. doi:10.1115/96-GT-188.
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Numerical simulations of the three-dimensional flow and heat transfer in a rectangular duct with a 180° bend were performed. Results are presented for Reynolds numbers of 17,000 and 37,000 and for aspect ratios of 0.5 and 1.0. A k-ω turbulence model with no reference to distance to a wall is used. Direct comparison between single block and multiblock grid calculations are made. Heat transfer and velocity distributions are compared to available literature with good agreement. The multi-block grid system is seen to produce more accurate results compared to a single-block grid with the same number of cells.

Commentary by Dr. Valentin Fuster
1996;():V004T09A018. doi:10.1115/96-GT-189.
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Predictions of the rate of heat transfer to the tip and shroud of a gas turbine rotor blade are presented. The simulations are performed with a multiblock computer code which solves the Reynolds Averaged Navier-Stokes equations. The effect of inlet boundary layer thickness as well as rotation rate on the tip and shroud heat transfer is examined. The predictions of the blade tip and shroud heat transfer are in reasonable agreement with the experimental measurements. Areas of large heat transfer rates are identified and physical reasoning for the phenomena presented.

Commentary by Dr. Valentin Fuster
1996;():V004T09A019. doi:10.1115/96-GT-200.
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Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems which rely on plate inserts. In this paper, it is shown that the surface which forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature sensitive liquid crystals to measure the surface temperature of large scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer has been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Commentary by Dr. Valentin Fuster
1996;():V004T09A020. doi:10.1115/96-GT-201.
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The present study explores the heat transfer enhancement induced by arrays of cubic fins. The fin element is either a cube or a diamond in shape. The array configurations studied include both inline and staggered arrays of seven rows and five columns. Both cubic arrays have the same geometric parameters, i.e., H/D=1, S/D=X/D=2.5, which are similar to those of earlier studies on circular pin-fin arrays. The present results indicate that the cube element in either array always yields the highest heat transfer, followed by diamond and circular pin-fin. Arrays with diamond-shaped elements generally cause the greatest pressure loss than those with either cubes or pin fins. For a given element shape, a staggered array generally produces higher heat transfer enhancement and pressure loss than the corresponding inline array. Cubic Arrays can be viable alternatives for pedestal cooling near a blade trailing edge.

Commentary by Dr. Valentin Fuster
1996;():V004T09A021. doi:10.1115/96-GT-207.
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Detailed studies are conducted on film effectiveness of inclined discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a configuration similar to that of a typical turbine blade and are angled at 30 and 90 degree to the surface in the spanwise and streamwise directions, respectively. A spoked-wheel type wake generator is used in this study to simulate periodically incoming wakes to turbine blades. In addition, two types of turbulence grids are used to elevate a free-stream turbulence intensity. We adopt three blowing ratios of the secondary air to the mainstream. Most of the dominant flow conditions are reproduced in this study except for the air density ratio of the secondary air and the main stream. For each of the blowing ratios, wall temperature around the surface of the test model are measured by thermocouples situated inside the model. The temperature is visualized using liquid crystals to obtain traces of the injected secondary air on the test surface, which consequently helps us interpret the data of the thermocouples.

Topics: Cooling , Wakes
Commentary by Dr. Valentin Fuster
1996;():V004T09A022. doi:10.1115/96-GT-208.
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This paper describes an investigation of the aerodynamic aspects of endwall film-cooling, in which the flow field downstream of a large-scale low-speed linear turbine cascade has been measured. The integrated losses and locations of secondary flow features with and without end wait film-cooling have been determined for variations of both the coolant supply pressure and injection location. Together with previous measurements of adiabatic film-cooling effectiveness and surface-flow visualisation, these results reveal the nature of the interactions between the ejected coolant and the flow in the blade passage. Measured hole massflows and a constant static pressure mixing analysis, together with the measured losses, allow the decomposition of the losses into three distinct entropy generation mechanisms: loss generation within the hole, loss generation due to the mixing of the coolant with the mainstream, and change in secondary loss generation in the blade passage. Results show that the loss generation within the coolant holes is substantial and that ejection into regions of low static pressure increases the loss per unit coolant massflow. Ejection upstream of the three-dimensional separation lines on the endwall changes secondary flow and reduces its associated losses. The results show that it is necessary to take the three-dimensional nature of the endwall flow into account in the design of endwall film-cooling configurations.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
1996;():V004T09A023. doi:10.1115/96-GT-209.
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The film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream, Understanding this interaction is important in order to explain the physical mechanisms involved in the rapid decrease of effectiveness which occurs close to the hole exit. Not surprisingly, it is this region which is not modeled satisfactorily with current film cooling models. This study uses a high frequency response temperature sensor which provides new information about the film cooling flow in terms of actual turbulence levels and probability density functions of the thermal field. Mean and rms temperature results are presented for 35° round holes at a momentum flux ratio of I = 0.16, at a density ratio of DR = 1.05. Probability density functions of the temperature indicate penetration of the mainstream into the coolant core, and ejection of coolant into the mainstream. Extreme excursions in the fluctuating temperature measurements suggests existence of strong intermittent flow structures responsible for dilution and dispersion of the coolant jets.

Commentary by Dr. Valentin Fuster
1996;():V004T09A024. doi:10.1115/96-GT-210.
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This paper describes work done in preparation for the measurement of stage efficiency in a short-duration shock-tunnel facility. Efficiency measurements in this facility require knowledge of the flow path pressure and temperature, rotating system moment of inertia, and mass flow. This paper describes in detail an improved temperature compensation technique for the pressure transducers (Kulite) to reduce thermal drift problems, and measurements of the rotating system moment of inertia. The temperature compensation has shown that the conversion to pressure is accurate to within 0.689 kPa (0.1 psi) over the 40°C test range. The measurement of the moment of inertia is shown to be accurate to within 0.7% of the average value.

Commentary by Dr. Valentin Fuster
1996;():V004T09A025. doi:10.1115/96-GT-221.
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A three-dimensional Navier-Stokes code has been used to compute the adiabatic effectiveness and heat transfer coefficient on a rotating film-cooled turbine blade. The blade chosen is the UTRC rotor with five film-cooling rows containing 83 holes, including three rows on the shower head with 49 holes, covering about 86% of the blade span. The mainstream is akin to that under real engine conditions with stagnation temperature = 1900 K and stagnation pressure = 3 MPa. The blade speed is taken to be 5200 rpm. The adiabatic effectiveness is higher for a rotating blade as compared to that for a stationary blade. Also, the direction of coolant injection from the shower-head holes affects considerably the effectiveness and heat transfer coefficient values on both the pressure and suction surfaces. In all cases, the heat transfer coefficient and adiabatic effectiveness are highly three-dimensional in the vicinity of holes but tend to become two-dimensional far downstream.

Commentary by Dr. Valentin Fuster
1996;():V004T09A026. doi:10.1115/96-GT-222.
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The emphasis of the present study is to understand the effects of various flowfield and geometrical parameters in the nearfield region of a scaled-up film-cooling hole on a flat test plate. The effect of these different parameters on adiabatic wall effectivenesses, heat transfer coefficients, discharge coefficients and the near-hole velocity field will be addressed. The geometrical parameters of concern include several angles of inclination and rotation of a cylindrical film-cooling hole and two different hole shapes — a fanshaped hole and a laidback fanshaped hole. The fluid dynamic parameters include both the internal and external Mach number as well as the mainstream-to-coolant ratios of total temperature, velocity, mass flux, and momentum flux. In particular, the interaction of a film-cooling jet being injected into a transonic mainstream will be studied.

This paper includes a detailed description of the test rig design as well as the measuring techniques. Firstly, tests revealing the operability of the test rig will be discussed. Finally, an outlook of the comprehensive experimental and numerical program will be given.

Topics: Shapes , Film cooling
Commentary by Dr. Valentin Fuster
1996;():V004T09A027. doi:10.1115/96-GT-223.
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The predictions from a three-dimensional Navier-Stokes code have been compared to the Nusselt number data obtained on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire span. This is the only film-cooled rotating blade over which experimental heat transfer data is available for the present comparison. Over 2.25 million grid points are used to compute the flow over the blade. Usually in a film cooling computation on a stationary blade, the computational domain is just one spanwise pitch of the film-cooling holes, with periodic boundary conditions in the span direction. However, for a rotating blade, the computational domain consists of the entire blade span from hub to tip, as well as the tip clearance region.

As far as the authors are aware of, the present work offers the first comparison of the prediction of surface heat transfer using a three dimensional CFD code with film injection and the measured heat flux on a fully film-cooled rotating transonic turbine blade. In a detailed comparison with the measured data on the suction surface, a reasonably good comparison is obtained, particularly near the hub section. On the pressure surface, however, the comparison between the data and the prediction is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present numerical computations.

Topics: Rotating blades
Commentary by Dr. Valentin Fuster
1996;():V004T09A028. doi:10.1115/96-GT-224.
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A new model is developed to predict laterally-averaged film cooling. At the injection location, the near-hole region is leapt over and the injectant is distributed according to an existing jet in cross flow model and experimental data. The subsequent dispersion of the injectant is simulated to reflect the augmented mixing and the 3-dimensionality of the flow field. The new model is calibrated to predict effectiveness and heat transfer using the experimental data bases of Schmidt et al. (1994), Sen et al. (1994), Kohli et al. (1994), and Sinha et al. (1991). The geometries include injection angles of 35° and 55° with compound angles of 0° and 60° and hole spacings of 3 and 6 diameters. The new model yields improved effectiveness predictions over previous 2-D models.

Commentary by Dr. Valentin Fuster
1996;():V004T09A029. doi:10.1115/96-GT-225.
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Over the past few years advances in thermochromic liquid crystal (TLC) thermography have improved its usefulness as a quantitative temperature measurement technique. Many of these improvements have been discussed in the literature but few have been directly applied to solving gas turbine heat transfer problems. The purpose of this work is to combine the best of these techniques into an advanced, easy to use, low cost system which can provide accurate, rapid and complete heat transfer data for advanced gas turbine development.

The older, more common technique of using narrow band liquid crystals to map isotherm distributions has been updated to use wide temperature range crystals with full hue-temperature calibrations over their entire response range with accuracy as good or better than thermocouples. The system consists of an RGB video camera, a hue, saturation and intensity (HS1) framegrabber, on-axis lighting and a linear thermal gradient TLC calibrator. Algorithms have been developed for automated data validation, spatial transformations of data taken on non-planar surfaces and superposition of multiple data sets to construct full field data over surfaces with wide ranges of heat transfer coefficients (h). Instead of yielding mean h, h at a few thermocouple locations or h at individual isotherms, this system provides continuous distributions of h.

These techniques have been used to map the heat transfer coefficient distributions in advanced power generation gas turbine internal cooling passages. These include serpentine passages with and without turbulators, leading edge passages and 180° rums. Results are presented in full field plots of heat transfer enhancement, Nu(x,y)/Nudb.

Commentary by Dr. Valentin Fuster
1996;():V004T09A030. doi:10.1115/96-GT-233.
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In spite of very significant progress in analytical and numerical methods during recent years, experimental techniques are still essential tools for the development of cooled turbine nozzles. This paper describes the major elements of the development process for cooled turbine nozzles with a primary emphasis on advanced experimental heat transfer techniques. Thermochromic liquid crystals were used to measure the internal (coolant side) heat transfer coefficients of a practical vane cooling design which has a combination of different heat transfer augmenting devices. A comparison of the results and analytical predictions provided validations of existing correlations which were developed from the generic cases (usually one type of augmenting device). The overall cooling design was evaluated in a full-scale annular hot cascade which maintained heat transfer similarity. The freestream turbulence level was measured with an in-house developed heat flux probe. Cooling effectiveness distribution was evaluated from the surface metal temperatures mapped with an in-house developed wide range temperature pyrometer. The test results led to the fine-tuning of the nozzle vane cooling design.

Topics: Nozzles , Turbines
Commentary by Dr. Valentin Fuster
1996;():V004T09A031. doi:10.1115/96-GT-234.
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A two-equation turbulence model with additional terms for Coriolis and rotational buoyancy has been used for prediction of heat transfer from the leading and trailing sides of rotating square and rectangular channels with radially outward flow. Test cases with different Reynolds and rotation numbers are considered. The coolant air used is pressurized and operating conditions are selected to closely match real turbine operating parameters. Results show that previous experimental data can be extrapolated to predict the heat transfer characteristics of coolant passages of actual turbine blades. The internal secondary flow vortex structures for some of the aspect ratio channels are found to be different from the expected vortex structures based on earlier lower rotation speed, lower temperature, and lower pressure operating conditions.

Commentary by Dr. Valentin Fuster
1996;():V004T09A032. doi:10.1115/96-GT-235.
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An analytical investigation has been made to identify and quantify critical parameters influencing the final result of a transient heat transfer experiment. The aim was to obtain a set of dimensionless parameters, that describe the interaction of the individual measured quantities in a compact form.

Among the wide variety of different kinds of heat transfer measurement techniques, the transient method, employing thermochromic liquid crystals, is very useful. It gives much detailed heat transfer information with a minimum effort in experimental time. The present paper focuses on this technique, although it is not the only choice for all kinds of applications, but it is the currently most frequently used one.

This paper provides the means to lay out an experiment, so that it yields acceptable results with respect to the constraints for a set of test boundary conditions.

Commentary by Dr. Valentin Fuster
1996;():V004T09A033. doi:10.1115/96-GT-236.
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Two color double pulsed Particle Image Velocimetry (PIV) measurements of simulated turbine film cooling flows have been made for blowing ratios of 0.5, 0.7, and 1.0 in the near field of the film cooling hole, x/d≤2.5. The effect of the vane wake on the rotor film cooling flow is simulated by periodically forcing the film cooling flows at the nnn dimensional reduced frequency. Phase locked measurements at 45 deg. increments of the periodic film forcing (0, 45, 90, 135, 180, 225, 270, and 315 deg.) for free stream turbulence levels of 1 and 17% have been made. The effects of reduced frequencies of 20 and 80, at free stream turbulence levels of 1 and 17% on the spreading of the film cooling jet are investigated. Increases in the jet spread with forcing and free stream turbulence are > 2 times those in the unforced 1% free stream turbulence case.

Commentary by Dr. Valentin Fuster
1996;():V004T09A034. doi:10.1115/96-GT-237.
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The determination of aerothermal loading plays a vital role in any performance or structural investigation of turbine hot-end components during both the design and in-service phases. This investigation considers the measurement and prediction of heat transfer on a nozzle guide vane in a linear cascade. The experimental method is based on a transient approach and requires that the gas and blade have the correct temperature difference. In this study the transient technique is facilitated by maintaining a constant external gas flow in a closed circuit cascade facility and moving a cooled MACOR blade rapidly into the cascade, displacing an aluminium dummy blade. For a short period of time the correct temperature ratio exists between the gas and blade. It is during this period that the change in the thin-film resistance is measured, which is transformed to represent surface heat transfer. The experimental data is compared to an analytical prediction using an Euler code for the bulk flow solution and a boundary layer code for surface heat transfer. The boundary layer code includes the effects of turbulence in the boundary layer, and the transitional nature of the boundary layer flow is also captured. The accuracy associated with the levels of heat transfer is shown to be good for two exit Mach numbers, although some variation is evident towards the trailing edge of the suction surface. The laminar, transitional and turbulent regions of the boundary layer show good correspondence.

Commentary by Dr. Valentin Fuster
1996;():V004T09A035. doi:10.1115/96-GT-299.
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A flat plate test section was used to study how surface roughness representative of an in-service turbine affects the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole geometry. The injection was from a single row of round film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. A range of momentum flux ratios was examined to characterize the adiabatic effectiveness and heat transfer performance. Streamwise distributions of adiabatic effectiveness and heat transfer coefficients were obtained along the hole center line, and lateral distributions extending to halfway between hole centerlines were obtained at selected streamwise locations to 90 hole diameters downstream. Two rough surfaces with a factor of two difference in roughness levels were compared to an aerodynamically smooth surface.

Both rough surfaces degraded the film cooling effectiveness with increasing degradation farther downstream. Degradation of film cooling effectiveness was greater at low momentum flux ratios. At momentum flux ratios high enough so that the cooling jets completely detached from the surface, the rough surfaces slightly increased adiabatic effectiveness in some cases. There was little difference in the effectiveness results between the two rough surfaces. Film cooling injection had little effect on heat transfer rates for any of the surfaces.

Commentary by Dr. Valentin Fuster
1996;():V004T09A036. doi:10.1115/96-GT-304.
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Comparisons are shown between predictions and experimental data for blade and end wall heat transfer. The comparisons are given for both vane and rotor geometries over an extensive range of Reynolds and Mach numbers. Comparisons are made with experimental data from a variety of sources. A number of turbulence models are available for predicting blade surface heat transfer, as well as aerodynamic performance. The results of an investigation to determine the turbulence model which gives the best agreement with experimental data over a wide range of test conditions are presented.

Commentary by Dr. Valentin Fuster
1996;():V004T09A037. doi:10.1115/96-GT-310.
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A standard CFD code with two-layer k-ε-model was used to calculate film cooling effectiveness of flat plate test cases. Experimental data from the literature were taken to perform extensive validation of the code for film cooling effectiveness prediction. Emphasis was put on injection of cooling gas through one row of cylindrical holes in the streamwise direction. Blowing ratio, density ratio, blowing angle, pitch, and hole length to diameter ratio were varied in a wide range. It was found that the code is well suited for the prediction of lateral averaged film cooling effectiveness for common film cooling conditions. A similarity analysis is presented for the prescribed film cooling problem to isolate the influence parameters of flow properties and geometry. A reduction of the parameters of influence was achieved using physical implications. The magnitude of the remaining parameters was compared for literature reported experimental results and gas turbine applications. It was found that experimental realized Reynolds and Eckert numbers are mostly far from turbine engine conditions. Therefore the validated CFD code was used to extrapolate the experimental configuration to engine like conditions. It was found that the examined Reynolds and Eckert numbers had no significant impact on lateral averaged film cooling effectiveness. It is hence possible to present a reduced but complete set of the governing influence parameters on the discussed film cooling problem.

Commentary by Dr. Valentin Fuster
1996;():V004T09A038. doi:10.1115/96-GT-312.
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In the design and development of modern gas turbine machines for efficient power generation in combined cycle applications, nozzle segments with airfoils and sidewalls need to be effectively cooled to operate in gas temperature environments in the excess of the melting point of the material of construction. Particular attention is given to the thermal evaluation as it affects component design life and performance. In this context, an optimization methodology is prescribed for inverse determination of required coolant heat transfer as a function of hot gas conditions and subjected to constraints associated with allowable metal temperature. A general boundary element method is used in the optimization process to provide a relatively fast and economically feasible design procedure. The optimized set of heat transfer results are converged when the external metal temperatures fall within acceptable limits. Once the magnitude and distribution of required coolant heat transfer coefficients are obtained, the cooling technique can be devised using available or referenced correlations for impingement jets through insert plates, banks of pin fins, turbulators, or just simply forced convection through internal passages. An illustrative example is presented with a Joukowski airfoil using a finite element method as an alternative method of solution for comparison and verification.

Commentary by Dr. Valentin Fuster
1996;():V004T09A039. doi:10.1115/96-GT-313.
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A detailed map of heat transfer coefficients has been measured in a converging blade cooling passage with 45 deg. discrete ribs on two opposite walls for a range of engine representative Re of 10,000 ∼ 50,000. Flow visualization showed that there were four different types of secondary flow created by the discrete ribs: skewed boundary layer, secondary flow in front of the rib, secondary flow behind the rib, swirling longitudinal vortex flow and for large rib heights there were vortex streets. The origin of these secondary flows and their structure are discussed together with their contribution to the local enhancement of heat transfer. The results were used to understand the mechanism of heat transfer enhancement using secondary flow created by rib turbulators and from this to develop new design methods for improved enhanced heat transfer.

Commentary by Dr. Valentin Fuster
1996;():V004T09A040. doi:10.1115/96-GT-351.
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Numerical results are presented for a three–dimensional discrete–jet in crossflow problem typical of a realistic film–cooling application in gas turbines. Key aspects of the study include: (1) Application of a systematic computational methodology that stresses accurate computational model of the physical problem, including simultaneous, fully–elliptic solution of the crossflow, film–hole, and plenum regions; high quality 3–D unstructured grid generation techniques which have yet to be documented for this class of problems; the use of a high order discretization scheme to significantly reduce numerical errors; and effective turbulence modelling; (2) A three–way comparison of results to both code validation quality experimental data and a previously documented structured grid simulation; and (3) Identification of sources of discrepancy between predicted and measured results, as well as recommendations to alleviate these discrepancies. Solutions were obtained with a multi–block, unstructured/adaptive grid, fully explicit, time–marching, Reynolds averaged Navier–Stokes code with multi-grid, local time stepping, and residual smoothing type acceleration techniques. The computational methodology was applied to the validation test case of a row of discrete jets on a flat plate with a streamwise injection angle of 35°, and two film–hole length–to–diameter ratios of 3.5 and 1.75. The density ratio for all cases was 2.0, blowing ratio was varied from 0.5 to 2.0, and free–stream turbulence intensity was 2%. The results demonstrate that the prescribed computational methodology yields consistently more accurate solutions for this class of problems than previous attempts published in the open literature. Sources of disagreement between measured and computed results have been identified, and recommendations made for future prediction of this class of problems.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
1996;():V004T09A041. doi:10.1115/96-GT-355.
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A liquid crystal technique was used to measure heat transfer coefficients in twelve test sections with square and trapezoidal cross-sectional areas representing blade midchord cooling cavities in a modern gas turbine. Full-length ribs were configured on suction side as well as pressure side walls while half-length ribs were mounted on partition walls between adjacent cooling cavities. Ribs were in staggered arrangements with a nominal blockage ratio of 22% and an angle of attack to the mainstream flow, α, of 90°. Heat transfer measurements were performed on the roughened walls with full-length as well as half-length ribs. Nusselt numbers, friction factors and thermal performances of all geometries are compared. The most important conclusion of this study is that the roughening of the partition walls enhances the heat transfer coefficients on those walls but, more importantly, enhances heat transfer coefficients on the primary walls considerably.

Commentary by Dr. Valentin Fuster
1996;():V004T09A042. doi:10.1115/96-GT-356.
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Three staggered 90° rib geometries corresponding to blockage ratios of 0.133, 0.167 and 0.25 were tested for pitch-to-height ratios of 5, 8.5 and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface averaged heat transfer coefficients and friction factors for ribs with rounded corners and those with sharp comers, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It was concluded that: a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. For the sharp-corner ribs, the rib average heat transfer coefficient increased with blockage ratio. However, when the corners were rounded, the trend depended on the level of roundness. b) High blockage ratio (e/Dh=0.25) ribs were insensitive to the pitch-to-height ratio. For the other two blockage ratios, the pitch-to-height ratio of 5 produced the lowest heat transfer coefficient. Results of the other two pitch-to-height ratios were very close, with the results of S/e = 10 slightly higher than those of S/e=8.5. c) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients for all cases except that of the smallest blockage ratio with S/e of 5. In that position, for the rib geometries tested, while the sharp-comer rib average heat transfer coefficients increased with the blockage ratio, the trend of the round-corner ribs depended on the level of roundness, r/e. d) Thermal performance decreased with the blockage ratio. While the smallest rib geometry at a pitch-to-height ratio of 10 had the highest thermal performance, thermal performance of high blockage ribs at a pitch-to-height ratio of 5 was the lowest. e) The general effects of rounding were a decrease in heat transfer coefficient for the midstream ribs and an increase in heat transfer coefficient for ribs in the furthest upstream position.

Commentary by Dr. Valentin Fuster
1996;():V004T09A043. doi:10.1115/96-GT-381.
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This paper presents data showing the improvement in cooling effectiveness of turbine vanes through the application of water-air cooling technology in an industrial/utility engine application. The technique utilizes a finely dispersed water-in-air mixture that impinges on the internal surfaces of turbine airfoils to produce very high cooling rates. An airfoil was designed to contain a standard impingement tube which distributes the water-air mixture over the inner surface of the airfoil. The water flash vaporizes off the airfoil inner wall. The resulting mixture of air-steam-water droplets is then routed through a pin fin array in the trailing edge region of the airfoil where additional water is vaporized. The mixture then exits the airfoil into the gas path through trailing edge slots.

Experimental measurements were made in a three-vane, linear, two-dimensional cascade. The principal independent parameters — Mach number, Reynolds number, wall-to-gas temperature ratio, and coolant-to-gas mass flow ratio — were maintained over ranges consistent with typical engine conditions. Five impingement tubes were utilized to study geometry scaling, impingement tube-to-airfoil wall gap spacing, impingement tube hole diameter, and impingement tube hole patterns. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, gas-to-coolant temperature ratio, water- and air-coolant-to-gas mass flow ratios, and impingement tube geometry.

Heat transfer effectiveness data obtained in this program demonstrated that overall cooling levels typical for air cooled vanes could be achieved with the water-air cooling technique with reductions of cooling air flow of significantly more than 50%.

Commentary by Dr. Valentin Fuster
1996;():V004T09A044. doi:10.1115/96-GT-386.
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The physical characteristics of surface roughness observed on 1st stage high pressure turbine vanes which had been in service for a long period were investigated in this study. Profilometry measurements were utilized to provide details of the surface roughness formed by deposits of foreign materials on different parts of the turbine vane. Typical measures of surface roughness such as centerline average roughness values were shown to be inadequate for characterizing roughness effects. Using a roughness shape parameter originally derived from regular roughness arrays, the turbine airfoil roughness was characterized in terms of equivalent sandgrain roughness in order to develop an appropriate simulation of the surface for laboratory experiments. Two rough surface test plates were designed and fabricated and these test plates were evaluated experimentally to quantify the heat transfer rate for flow conditions similar to that which occur on the turbine airfoil. Although the roughness levels on the two test plates were different by a factor of two, both surfaces caused similar 50% increases in heat transfer rates relative to a smooth surface. The effects of high free-stream turbulence, with turbulence levels from 10% to 17%, were also investigated. Combined free-stream turbulence and surface roughness effects were found to be additive, resulting in as much as a 100% increase in heat transfer rate.

Commentary by Dr. Valentin Fuster
1996;():V004T09A045. doi:10.1115/96-GT-387.
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The effect of channel rotation on jet impingement cooling by arrays of circular jets in two channels was studied. Jet flow direction was in the direction of rotation in one channel and opposite to the rotation direction in the other channel. The jets impinged normally on two smooth target walls. Heat transfer results are presented for these two target walls, for the jet walls containing the jet producing orifices, and for side walls connecting the target and jet walls. The flow exited the channels in a single direction, radially outward, creating a cross flow on jets at larger radii. The mean test model radius to jet diameter ratio was 397. The jet rotation number was varied from 0.0 to 0.0028 and the isolated effects of jet Reynolds number (5000 and 10000), and wall-to-coolant temperature difference ratio (0.0855 and 0.129) were measured. The results for non-rotating conditions show that the Nusselt numbers for the target and jet walls in both channels are about the same and are greater than those for the side walls of both channels. However, as rotation number increases, the heat transfer coefficients for all walls in both channels decrease up to 20% below those results which correspond to non-rotating conditions. As the wall-to-coolant temperature difference ratio increases, heat transfer coefficient decreases up to 10% with other parameters held constant.

Commentary by Dr. Valentin Fuster
1996;():V004T09A046. doi:10.1115/96-GT-388.
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The local Mach number and heat transfer coefficient over the aerofoil surfaces and endwalls of a transonic gas turbine nozzle guide vane have been calculated. The computations were performed by solving the time averaged Navier-Stokes equations using a fully three-dimensional computational code (CFDS) which is well established at Rolls-Royce.

A model to predict the effects of roughness has been incorporated into CFDS and heat transfer levels have been calculated for both hydraulically smooth and transitionally rough surfaces. The roughness influences the calculations in two ways; firstly the mixing length at a certain height above the surface is increased; secondly the wall function used to reconcile the wall condition with the first grid point above the wall is also altered. The first involves a relatively straightforward shift of the origin in the van Driest damping function description, the second requires an integration of the momentum equation across the wall layer. A similar treatment applies to the energy equation.

The calculations are compared with experimental contours of heat transfer coefficient obtained using both thin film gauges and the transient liquid crystal technique. Measurements were performed using both hydraulically smooth and roughened surfaces, and at engine-representative Mach and Reynolds numbers. The heat transfer results are discussed and interpreted in terms of surface-shear flow visualisation using oil and dye techniques.

Commentary by Dr. Valentin Fuster
1996;():V004T09A047. doi:10.1115/96-GT-428.
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Full heat transfer coefficient and static pressure distributions have been measured on the target surface under impinging jets formed by sharp-edged and large entry radius holes. These geometries are representative of impingement holes in a gas turbine blade manufactured by laser cutting and by casting, respectively. Target surface heat transfer has been measured in a large scale perspex rig using both the transient liquid crystal technique and hot thin film gauges. A range of jet Reynolds numbers, representative of engine conditions, has been investigated. The velocity variation has been calculated from static pressure measurements on the impingement target surface. The heat transfer to the target surface is discussed in terms of the interpreted flow field.

Commentary by Dr. Valentin Fuster
1996;():V004T09A048. doi:10.1115/96-GT-438.
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The ammonia and diazo technique with CO2-calibration for highly resolving measurement of adiabatic film cooling effectiveness distribution has been developed and improved with respect to high accuracy.

Both parts of the technique are based on the analogy between heat and mass transfer. In the ammonia and diazo part a mixture of ammonia and air is injected through the film cooling holes. Downstream of the injection a diazo film is mounted on the experimental surface. Depending on the local ammonia concentrations along the wall the diazo film turns blue. In the CO2-calibration part carbon dioxide is used as a tracer gas. Gas samples are sucked off and analyzed, thus giving the adiabatic film cooling effectiveness at certain locations on the surface. Relating the effectiveness values to the color intensities of the diazo film at the corresponding locations a calibration curve is derived.

This calibration can be applied to the whole color distribution of the diazo film resulting in a highly resolved distribution of the adiabatic film cooling effectiveness. The scattering of the measured values along the calibration curve directly indicates the quality of the measurement.

The ammonia and diazo technique with CO2-calibration has been applied to injection through a row of holes (α = 35°, p/D = 3) in the flat wall of a wind tnnnel for different blowing rates. The results show a very good suitability of this technique, especially, but not only, if the region around the film cooling holes is of special interest.

Commentary by Dr. Valentin Fuster
1996;():V004T09A049. doi:10.1115/96-GT-462.
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A flat plate test section was used to study how high free-stream turbulence with large turbulence length scales, representative of the turbine environment, affect the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole film cooling geometry. This study also examined cooling performance with combined high free-stream turbulence and a rough surface which simulated the roughness representative of an in-service turbine. The injection was from a single row of film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. Streamwise and lateral distributions of adiabatic effectiveness and heat transfer coefficients were obtained at locations from 2 to 90 hole diameters downstream.

At small to moderate momentum flux ratios, which would normally be considered optimum blowing conditions, high free-stream turbulence dramatically decreased adiabatic effectiveness. However, at large momentum flux ratios, conditions for which the film cooling jet would normally be detached, high free-stream turbulence caused an increase in adiabatic effectiveness. The combination of high free-stream turbulence with surface roughness resulted in an increase in adiabatic effectiveness relative to the smooth wall with high free-stream turbulence. Heat transfer rates were relatively unaffected by a film cooling injection. The key result from this study was a substantial increase in the momentum flux ratios for maximum film cooling performance which occurred for high free-stream turbulence and surface roughness conditions which are more representative of actual turbine conditions.

Commentary by Dr. Valentin Fuster
1996;():V004T09A050. doi:10.1115/96-GT-463.
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The dependence of heat transfer on film cooling near the leading edge of a blade was investigated using the naphthalene sublimation technique and applying the analogy between heat and mass transfer. Therefore, the local sublimation rate with and without film cooling was measured. The symmetric leading edge was cooled by an air mass flow out of two staggered rows of holes. The measurements were carried out with a constant Reynolds number Re = 80000, different incidence angles φ = 0° to 10° and a blowing rate varying from M = 0.3 to 2.5.

The flow without film cooling was visualized around the leading edge with smoke to indicate the existence of separation bubbles. To determine the dependence of incidence angle and blowing rate on jet trajectories, smoke was mixed to the cooling air.

The mass transfer coefficient was determined with the naphthalene sublimation technique. Due to the high resolution of the sublimation technique the local mass transfer distribution around the cooling holes could also be measured. Furthermore, the location of stagnation points and separation bubbles were investigated.

The results of the tests without film cooling were also compared with those obtained by observing stagnation point mass transfer on a cylinder and with those by laminar flow across a flat plate. The mass transfer coefficient of film cooling experiments was related to the mass transfer coefficient without film cooling to describe the local dependence of heat transfer coefficient on film cooling. An increase on relativ heat transfer near the film cooling holes is obtained by increasing the blowing rate. No further influence on heat transfer along the pressure side is detected for an incidence angle larger than 10° as the cooling films were shifted around the leading edge from the pressure to the suction side.

Commentary by Dr. Valentin Fuster
1996;():V004T09A051. doi:10.1115/96-GT-474.
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The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls: all four walls along each pass are active and have mass transfer from their surfaces but the ribs are non-participating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected inter-rib modules. Results are presented for Reynolds number in the range of 5,000 to 40,000. pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the inter-rib profiles along the ribbed walls more uniform. Along the side walls, horseshoe vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

Commentary by Dr. Valentin Fuster
1996;():V004T09A052. doi:10.1115/96-GT-476.
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This paper reports laser Doppler anemometry (LDA) and wall pressure measurements of turbulent flow in a square-sectioned, rotating U-bend typical of coolant passages employed in modern gas turbine blades. In the upstream and downstream tangents, the pressure and suction (inner and outer) surfaces are roughened with discrete square-sectioned ribs in a staggered arrangement for a rib-height to duct-diameter ratio of 0.1. Three cases have been examined at a passage Reynolds number of 105: a stationary case; a case of positive rotation (the pressure side coinciding with the outer side of the U-bend) at a rotation number (Ro=ΩD/Um) of 0.2; and a case of negative rotation at Ro=−0.2. Measurements have been obtained along the symmetry plane of the duct. In the upstream section, the separation bubble behind each rib is about 2.5 rib-heights long. Rotation displaces the high momentum fluid towards the pressure side, enhances turbulence along the pressure side and suppresses turbulence along the suction side. The introduction of ribs in the straight sections reduces the size of the separation bubble along the inner wall of the U-bend, by raising turbulence levels at the bend entry; it also causes the formation of an additional separation bubble over the first rib interval along the outer wall, downstream of the bend exit. Rotation also modifies the mean flow development within the U-bend, with negative rotation speeding up the flow along the inner wall and causing a wider inner-wall separation bubble at exit. Turbulence levels within the bend are generally increased by rotation and, over the first two diameters downstream of the bend, negative rotation increases turbulence while positive rotation on the whole has the opposite effect.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
1996;():V004T09A053. doi:10.1115/96-GT-478.
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A phenomenological model is presented that relates freestream turbulence to the augmentation of stagnation-point surface flux quantities. The model requires the turbulence intensity, the longitudinal scale of the turbulence, and the energy spectra as inputs for the unsteady velocity at the edge of the near-wall viscous region. The form of the edge velocity contains both pulsations of the incoming flow and oscillations of the streamline.

Incompressible results using a single fluctuating component are presented within the stagnation region of a two-dimensional cylinder. The time-averaged Froessling number is determined from the computations. These predictions are compared to existing incompressible experimental data. Additionally, the variations in the surface flux quantities with the longitudinal scale of the incoming freestream turbulence, the Reynolds number, and the freestream turbulence intensity are considered.

Commentary by Dr. Valentin Fuster
1996;():V004T09A054. doi:10.1115/96-GT-490.
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Laser holographic interferometry and pressure measurements are presented for the effects of rib-to-duct height ratio (H/2B), rib pitch-to-height ratio (Pi/H), and Reynolds number (Re) on the spatially periodic-fully developed turbulent heat transfer and friction in a rectangular duct of width-to-height ratio of 4:1 with an array of ribs detached from one wall at a clearance to rib-height ratio of 0.38. The range of H/2B, Pi/H, and Re examined were 0.13 to 0.26, 7 to 13, and 5×103 to 5×104, respectively. The difference in the H/2B dependence of the thermal performance between the detached and attached solid-rib array is documented. H/2B=0.17 and Pi/H=10 are found to provide the best thermal performance for the range of parameters tested. Compact heat transfer and friction correlations are developed. Additionally, it is found that heat transfer augmentation with a detached solid-rib array is superior to with a detached perforated-rib array, and the mechanism responsible for the difference is revealed by the complementary flow visualization results.

Commentary by Dr. Valentin Fuster
1996;():V004T09A055. doi:10.1115/96-GT-491.
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It is shown here by dimensional analysis that the near-wall flow field of an effusion cooled combustor, can be scaled if the Reynolds, Mach and Prandtl numbers and the temperature and velocity ratios are kept constant. It is also demonstrated that a practical model experiment can be designed, which fulfils all the scaling laws. A test rig meeting these requirements has been designed, built and tested. The experimental conditions have been chosen to correspond to the conditions usually met in a real effusion cooled combustion chamber.

One geometrical configuration has been investigated. This consists of one transverse row of holes drilled with a 30° angle to the wall through which the cooling air enters into a cross flowing mainstream. The mean values of all three velocity components and the three normal fluctuating Reynolds stresses as well as the mean temperature have been measured in a large number of points surrounding the central injection hole.

Experiments were carried out for jet-to mainstream density ratios of 1.2 and 1.8 and the results indicate that realistic density ratios are necessary to provide data directly applicable in effusion cooling design.

Topics: Temperature , Jets
Commentary by Dr. Valentin Fuster
1996;():V004T09A056. doi:10.1115/96-GT-492.
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Published information on the discharge coefficient of film cooling holes is classified in terms of the hole geometry, the external flow conditions at inlet and outlet, and the method of evaluation. This may be either theoretical or experimental.

The information is reviewed primarily in the context of its use for evaluating discharge coefficients for conditions not directly covered by published data. It is shown that potential flow analyses can give acceptable accuracy for simple geometries with crossflows, while more complex cases require the use of correlated data which may be incorporated in a range of predictive schemes.

Deficiencies and inconsistencies in the published information are highlighted, and future developments are discussed.

Commentary by Dr. Valentin Fuster
1996;():V004T09A057. doi:10.1115/96-GT-526.
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Evaluation of wall jet cooling inside of a gas turbine blade was accomplished. The wall jets are produced by confining the internal flow so that it must pass through narrow gaps and along the blade skin inner surfaces. Flow structure of the jets was revealed using polarization-optical visualization and laser Doppler anemometry. On the basis of analysis of the photos and of the flow turbulence spectra, the jet’s external boundary was identified. Diagrams of velocities, given in a non-dimensional form, for both the early development and downstream areas of the jet were obtained. Similarity solutions for local convective heat transfer to the confined wall jet were provided. The computational results agree well with the experimental data.

Commentary by Dr. Valentin Fuster
1996;():V004T09A058. doi:10.1115/96-GT-529.
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The interactions of boundary layer flow temperature fluctuations (t′) and velocity fluctuations (u′, v′) together with surface heat flux fluctuations (q′) have been investigated experimentally in a flat plate turbulent boundary layer in order to better understand time-resolved interactions between flow unsteadiness and surface heat flux. A Heat Flux Microsensor (HFM) was placed on a heated flat plate beneath a turbulent wall jet, and a split-film boundary layer probe was traversed above it together with a cold-wire temperature probe. The recorded simultaneous time-resolved u′v′t′q′ data can be correlated across the boundary layer. Results indicate that wall heat transfer (both mean and fluctuating components) is controlled by the u′ fluctuating velocity field. In the presence of high free-stream turbulence (FST), the heat flux is largely controlled by free stream eddies of large size and energy reaching deep into the boundary layer, such that heat flux spectra can be determined from the free-stream velocity field. This is evidenced by uq coherence present across the boundary layer, as well as by similarity in heat flux and u velocity spectra, and by the presence of large velocity scales down to the nearest wall measuring location just above the laminar sublayer.

Commentary by Dr. Valentin Fuster
1996;():V004T09A059. doi:10.1115/96-GT-534.
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The gas temperature distribution is important in the measurement and the definition of heat transfer to various gas turbine cooling problems. This paper describes a novel technique which employs encapsulated thermochromic liquid crystals on a fine nylon mesh to give virtually instantaneous gas temperature distribution measurement. The hue value of the liquid crystal on the mesh was calibrated to the gas temperature for a broad response crystal, in the range of 22–40°C, and for a narrow band crystal from 29–31°C. Data processing issues specific to the application of liquid crystals on porous target are discussed and the results of investigations provided. Finally, applications that demonstrate the viability of the method are given.

Commentary by Dr. Valentin Fuster
1996;():V004T09A060. doi:10.1115/96-GT-537.
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Calculations of the effects of high free stream turbulence (FST) on heat transfer and skin friction in a flat plate turbulent boundary layer using different k-ε models (Launder-Sharma, K-Y Chien, Lam-Bremhorsi and Jones-Launder) are presented. This study was carried out in order to investigate the prediction capabilities of these models under high FST conditions. In doing so, TEXSTAN, a partial differential equation solver which is based on the ideas of Patankar and Spalding and solves steady-flow boundary layer equations, was used. Firstly, these models were compared as to how they predicted very low FST (≤ 1% turbulence intensity) cases. These baseline cases were tested by comparing predictions with both experimental data and empirical correlations. Then, these models were used in order to determine the effect of high FST (>5% turbulence intensity) on heat transfer and skin friction and compared with experimental data. Predictions for heat transfer and skin friction coefficient for all the turbulence intensities tested by all the models agreed well (within 1–8%) with experimental data. However, all these models predicted poorly the dissipation of turbulent kinetic energy (TKE) in the free stream and TKE profiles. Physical reasoning as to why the aforementioned models differ in their predictions and the probable cause of poor prediction of free-stream TKE and TKE profiles are given.

Commentary by Dr. Valentin Fuster
1996;():V004T09A061. doi:10.1115/96-GT-541.
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The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to beight ratio. The blockage ratio of these square obstacles was 10% or 20% depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30000.

The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on 2D LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature.

This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/Dh=0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

Commentary by Dr. Valentin Fuster
1996;():V004T09A062. doi:10.1115/96-GT-542.
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The local heat transfer coefficient distribution over all four walls of a large scale model of a gas turbine cooling passage have been measured in great detail. A new method of determining the heat transfer coefficient to the rib surface has been developed and the contribution of the rib, at 5% blockage, to the overall roughened heat transfer coefficient was found to be considerable. The vortex dominated flow field was interpreted from the detailed form of the measured local heat transfer contours. Computational Fluid Dynamics calculations support this model of the flow and yield friction factors which agree with measured values. Advances in the heat transfer measuring technique and data analysis procedure which confirm the accuracy of the transient method are described in full.

Commentary by Dr. Valentin Fuster

Electric Power

1996;():V004T10A001. doi:10.1115/96-GT-001.
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IHI is developing a new heavy duty gas turbine engine for 2MW class co-generation plants, which is called IM270. This engine is a simple cycle and single-spool gas turbine engine. Target thermal efficiency is the higher level in the same class engines. A dry low NOx combustion system has been developed to clear the strictest emission regulation in Japan. All parts of the IM270 are designed with long life for low maintenance cost. It is planned that the IM270 will be applied to a dual fluid system, emergency generation plant, machine drive engine and so on, as shown in Fig.1.

The development program of IM270 for the co-generation plant is progress. The first prototype engine test has been started. It has been confirmed that the mechanical design and the dry low NOx system are practical. The component tuning test is being executed. On the other hand, the component test is concurrently in progress. The first production engine is being manufactured to execute the endurance test using a co-generation plant at the IHI Kure factory.

This paper provides the conceptual design and status of the IM270 basic engine development program.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A002. doi:10.1115/96-GT-005.
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This paper describes the technologies that are being developed or extended beyond the current state-of-the-art to achieve Advanced Turbine Systems (ATS) Program goals. The Westinghouse ATS plant is an advanced closed-loop enoled combined cycle, based on an advanced gas turbine engine incorporating novel design concepts and enhancements of existing technologies. The ATS engine is a fuel-flexible design operating nn natural gas with provisions fnr future conversion to coal or biomass fuels. It is based nn proven concepts employed in 501F and 501G engines. To achieve the required performance and reliability the engine will include closed-loop steam cooling, advanced materials and coatings, and enhanced component performance. To minimize NOx emissions, an ultra-low NOx combustion system will be incorporated. To ensure technical success, development programs are being conducted on the following: closed-loop steam cooling, advanced materials and coatings, component aerodynamic performance, flow visualization, optical diagnostics, combustion generated noise, and catalytic combustion.

Commentary by Dr. Valentin Fuster
1996;():V004T10A003. doi:10.1115/96-GT-006.
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The U.S. Department of Energy (DOE) has established a government/industry partnership program to greatly improve the capabilities of U.S. gas turbine technology. A new and challenging program named the Advanced Turbine Systems Program (ATS) has been initiated by DOE. The technical and business objectives of this initiative are to challenge the bounds of high performance capabilities of gas turbines, meet stringent environmental requirements, and produce lower cost electric power and cogeneration steam. This program will also yield greater societal benefits through continued expansion of high skilled U.S. jobs and export of U.S. products world wide.

A progress report on the ATS program pertaining to program status at DOE will be presented and reviewed in this paper. A preliminary design of an industrial advanced turbine system configuration will also be outlined in the paper. The technical challenges; advanced critical technologies incorporation, analytical and experimental solutions, and test results of an advanced gas turbine meeting the DOE goals will be described and discussed.

Commentary by Dr. Valentin Fuster
1996;():V004T10A004. doi:10.1115/96-GT-007.
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In recent years there has been an increased interest in the burning of ash forming liquid fuel oils including applications where fuel treatment is required.

The final decision of fuel type to use depends on several economic factors. These include the delivered price, cost of fuel treatment, cost of modifying the fuel handling system, and the increased maintenance costs associated with the grade of fuel. The ultimate decision on the burning of any fuel, including those fuel oils which require treatment is generally an economic choice, rather than a technical choice. There is however a broad end user lack of knowledge and understanding of the implications of burning ash forming liquid fuel oils. There is only limited documentation available detailing the considerations required to allow the upper and lower economic factors to be bounded.

It has been demonstrated that with careful attention to the fuel treatment process and the handling and operating practices, combustion turbines can, within certain limitations, successfully burn a wide range of liquid fuels.

Commentary by Dr. Valentin Fuster
1996;():V004T10A005. doi:10.1115/96-GT-008.
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IGCC (Integrated Gasification Combined Cycle) plants for large scale power generation are becoming more and more attractive.

For a gas turbine generating set to operate on Medium BTU gas, it takes dedicated design of both engine and auxiliaries.

A new combustion section, with extensive test support, has been developed. Alternative options to reduce inlet air flow and NOx emissions have been compared and appropriate solutions adopted. All auxiliaries systems have been modified according to the gas fuel characteristics.

Integration between plant systems has been carefully evaluated and a control system implemented in order to reach maximum reliability.

The paper deals with different technical aspects of the engine as well as the plant design.

Commentary by Dr. Valentin Fuster
1996;():V004T10A006. doi:10.1115/96-GT-009.
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Steam-injected gas turbines have a multitude of advantages, but they suffer from the inability to recover precious demineralized water. The present paper describes the test conditions and results of steam injection along with an attempt to achieve water recovery, which were obtained through a series of tests conducted on a S1A-02 small-sized industrial gas turbine. A water recovery device incorporating a compact finned spiral plate cooling condenser equipped with filter screens has been designed for the said gas turbine and a 100% water recovery (based on the design point) was attained.

Commentary by Dr. Valentin Fuster
1996;():V004T10A007. doi:10.1115/96-GT-010.
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A well reported, industry-wide problem with simple cycle peaking gas turbines installed near residences is excessive low frequency airborne noise, sometimes termed “infrasound.” If the noise level is high enough, it can cause perceptible vibration of windows and frame buildings, and provoke an adverse response from the community. Such a situation recently occurred after construction of a four unit GT 11N1 peaking station. A team of specialists and outside consultants was formed to investigate the problem, and a development program found that a thick absorber could be effective against infrasound. This led to the design of a thick panel absorber which was installed at the rear of a 90 degree turn in the exhaust system. Field testing verified that the low frequency noise from the turbine exhaust was reduced by 5.9 and 6.7 dB in the 31.5 and 63 Hz octave bands respectively, and by 5.5 dB(C) overall.

Commentary by Dr. Valentin Fuster
1996;():V004T10A008. doi:10.1115/96-GT-011.
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A revolutionary step has been taken in the development of the Next Advance in Power Generation Systems — “H” Technology Combined Cycle. This new gas turbine combined cycle system increases thermal performance to the 60% level by increasing gas turbine operating conditions to 2600°F (1430°C) at a pressure ratio of 23 to 1. This represents a significant increase in operating temperature for the gas turbine. However, the potential for single digit NOx levels (based upon 15% O2 in the exhaust) has been retained. The combined effect of performance increase and environmental control is achieved by an innovative closed loop steam cooling system which tightly integrated the gas turbine and steam turbine cycles.

Although a significant advance has been taken in performance, the new power generation system has been configured with a substantial number of proven concepts and technology programs are ongoing to validate the new features. The technical activities which support the introduction of the new turbine system have reached a point in the development cycle where the results are integrated into the design methods. This has permitted the “H” Technology to achieve a design readiness status and the first unit will be under test in late 1997.

Commentary by Dr. Valentin Fuster
1996;():V004T10A009. doi:10.1115/96-GT-013.
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Today’s competitive world of Independent Power Producers and electric wheeling has increased demand for lower operating and maintenance costs and increased revenues. This need is driving gas turbine research and development. Application of advanced technology to operating units can increase output, improve total plant efficiency, increase steam production and reduce maintenance costs. Cogen Technologies is one owner that has applied advanced technology to uprate five Frame 7EA gas turbines at its Linden plant and one unit at its Camden facility. At the Linden plant, total plant efficiency was improved by more than 2%.

This paper will discuss the components included in these advanced technology uprates, the gas turbine and combined-cycle plant performance improvements that were realized, and an economic model that can be used to evaluate the potential benefits of an uprate.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A010. doi:10.1115/96-GT-014.
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This paper will describe how Westinghouse approaches the design of new combustion turbines to ensure the same high reliability and availability as in its present products. The paper describes the risk analysis process, design verification, and methodology used in the design of the 501G combustion turbine together with Westinghouse’s design philosophy for reliable design.

Commentary by Dr. Valentin Fuster
1996;():V004T10A011. doi:10.1115/96-GT-016.
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It is very essential to raise the thermal efficiency of combined cycle plants from the viewpoint of energy saving and environmental protection. Tohoku Electric Power Co., Inc. and Toshiba Corporation in Japan have jointly studied the next generation of combined cycle system using 1500 °C class gas turbine.

A promising cooling technology for the vanes using steam was developed. The blades are cooled by air, adopting the impingement cooling, the film cooling and so on. The cooling effectiveness was confirmed both for the vanes and the blades using hot wind tunnel. This paper describes the design features of the vanes and the blades, and the results of the verification tests using hot wind tunnel.

Commentary by Dr. Valentin Fuster
1996;():V004T10A012. doi:10.1115/96-GT-020.
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Increased competition fostered by changes in legislation governing power generation entities has engendered a need to closely assess the economics of operating older-electric generating units. Decisions must be made as to whether these units should be retired and replaced with new, greenfield generation capacity, whether capacity should be purchased from other generation companies, or whether such units should be repowered in some way. The repowering alternative has merit when economic factors and environmental considerations show it to project the least cost of electricity over other choices. The chief advantages of repowering, include use of existing real estate and infrastructure, existing transmission facilities and staffing. Since the repowered plant usually emits less stack gas pollutants per unit of energy generated then the original plant, environmental benefits can also accrue.

Various types of gas turbine based repowering options for steam electric plants are presented. All the approaches discussed involve the addition of gas turbines to the cycle and the consequent benefit of some form of combined cycle operation. This option includes boiler retirement (and replacement with combined cycle), hot or warm windbox repowering (the boiler is retained and a gas turbine topping cycle is added), feedwater heating repowering (the gas turbine exhaust heats feedwater), and site repowering (only the site infrastructure is re-used as the site for a combined cycle). Business considerations are discussed in terms of their impact on the decision to repower and technology selection. An example involving feedwater heater repowering is used to illustrate the interaction between the business and technical aspects of repowering.

Commentary by Dr. Valentin Fuster
1996;():V004T10A013. doi:10.1115/96-GT-250.
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The combination of a topping Brayton (gas turbine) cycle with an existing Rankine (boiler-steam turbine) cycle for improved overall cycle heat rate has been very successful in the Netherlands.

In the years 1985–1989 10 gas-fired power plants with a capacity of nearly 4000 MW were substantially modernized by adding a gas turbine topping cycle.

In all these cases the Hot Wind box repowering or Windbox repowering with a supplementary boiler option was chosen.

Besides the improvement of the heat rate it was remarkable that a NOx-emission reduction was achieved between 50 and 85%.

So far more than 500,000 hours experience with hot windbox is available.

If NOx-reduction becomes very important windbox repowering is the best option to modernize power plants.

Commentary by Dr. Valentin Fuster
1996;():V004T10A014. doi:10.1115/96-GT-280.
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In 1992, Westinghouse Electric Corporation and Rolls-Royce signed a technology transfer agreement. The initial application for this aeroengine technology was the design by Westinghouse of the turbine for the 1500°C turbine inlet temperature, 58% (net) combined cycle efficiency, 501G engine. A key ingredient of the large jump in combined cycle efficiency over that of its predecessor, the 501F, was the reduction in the surface area of the first 3 cooled turbine stages. This reduction was made possible by the application of aerodynamic design and analysis which allowed accurate prediction of suction surface boundary layer growth in a 3D viscous environment. Thus, the number of aerofoils or the aerofoil chords were reduced in each cooled row, until the suction surface boundary layers were predicted to be a specified margin from separation at the trailing edge.

Since the resulting aerofoil loading (back surface diffusion) was higher than previous Westinghouse experience, a 0.32 scale model of a first stage turbine was built and tested in a cold rig at the National Research Council of Canada (NRCC), to substantiate the design codes when applied to industrial turbines. The purpose of the test was threefold: (1) to verify that higher levels of back surface diffusion were possible without boundary layer separation, (2) to verify that aeroengine turbine empirical loss/efficiency prediction correlations were applicable to industrial turbines, and (3) to see how well the single row, 3D, steady, Navier Stokes analysis code used during design predicted actual swallowing capacity, and radial variations in turning and loss.

The paper will describe the aerodynamic design tools and their validation, the test facility, hardware, measurement techniques, test results, and comparisons of prediction vs measurement, thus confirming the applicability of aeroengine aerodynamic technology to the design of large industrial gas turbines.

Commentary by Dr. Valentin Fuster
1996;():V004T10A015. doi:10.1115/96-GT-291.
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In the 80’s and early 90’s, in the Netherlands 11 combi blocks with prefitted gas turbines have been built. This repowering programme increased the efficiency of the units involved by several percentage points. Additionally, the commissioning of the five 335 MWe units at the Eems power station is in progress and plans exist for a farther seven 250 MW heat and power stations. This means that by 2002 the generating industry will be operating seventy-five gas turbines with a total gas turbine power of 5700 MWe. These data serve to illustrate mat gas turbines will be the workhorse of the Dutch generating industry in the coming decades, and that security of supply, efficiency, emissions and generating cost will to a large extent be determined by the gas turbine. However, the introduction of the gas turbine, driven by the possibility of high-efficiency electricity generation in e.g. combined cycle units, the increase in scale of the machines and the fact that they are increasingly being used in base load units have also led to problems and forced unavailability, as will be shown under goals of the project. The problems are related to creep, thermal stresses and fatigue of combustion chambers, turbine rotor blades, rotors etc. Apart from these problem areas, other subjects of interest are optimization of inlet air filtering and compressor cleaning. It is the Dutch Electricity Production industry who realized that a substantial R&D effort is necessary to solve those user related problems and formulated the execution of the target project Gas Turbines.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A016. doi:10.1115/96-GT-292.
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This paper describes the status of the Collaborative Advanced Gas Turbine (CAGT) Program’s initiative to commercialize interCooled AeroDerivative gas turbine (ICAD) technology. CAGT is a consortium of domestic and international electric companies, gas companies and research organizations. ICAD gas turbine technology was selected by CAGT member companies and potential suppliers in a competitive $5 million screening study of various advanced gas turbine options in the 1992–94 time frame. Efforts to commercialize ICAD began in 1994–95. The most attractive ICAD gas turbine options were based on high thrust engines produced by General Electric. Pratt & Whitney and Rolls Royce aircraft divisions. Simple cycle ICAD represents a new intermediate load gas turbine product class with costs and performance unlike any other product available today. Simple cycle efficiencies will approach Chose of many operating combined cycles, but with the low capital costs and rapid start times of a peaking gas turbine. ICAD simple cycle units would be in the 100–130 MW size range with efficiencies in the range of 45–48% + LHV and combined cycle efficiencies potentially as high as 60% + LHV. All efficiencies are presented in the paper in lower heating value (LHV). ICAD gas turbines will eddress a wide range of simple cycle, cogeneration. innovative repowering, combined cycle, distributed generation and renewable energy applications. CAGT members have several projects underway with the goal of the first ICAD unit to begin operation before the year 2000. Industry restructuring has reduced near-term demand for new generation in the United States with a corresponding drop in gas turbine prices. Given the large development cost for any new gas turbine product, potential ICAD suppliers have indicated the need for a launch order to proceed with development. CAGT is pursuing a number of project development and strategic alliance strategies globally to organize a launch order in the range of 10–15 projects. Efforts are also underway to examine options for demonstrating ICAD on a smaller scale (Small ICAD or SICAD) which would address the emerging market for distributed generation. CAGT members feel the low costs and flexibility offered by ICAD could be a significant source of competitive advantage in restructuring electric markets. CAGT members invite others to join the program.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A017. doi:10.1115/96-GT-293.
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The Tempest is the most recent power generation package produced by European Gas Turbines in England. It is currently in the evaluation phase of a 3 year program leading to production in 1996 at 7.5MWe and single-shaft configuration.

The machine has been designed for base load operation using gas and liquid fuels and is particularly suitable for combined heat and power applications. It is a development of the existing Typhoon and Tornado family of engines but includes a number of features to enhance its performance.

This paper discusses the design techniques and describes the gas turbine engine core. It also presents the design validation and service recommendations.

Commentary by Dr. Valentin Fuster
1996;():V004T10A018. doi:10.1115/96-GT-294.
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There is a strong demand for efficient and clean power generation systems which can cope with the energy shortage and the global environmental problems.

As one of the measures to meet this demand, Tohoku Electric Power Company, in cooperation with the three domestic gas turbine manufacturers, has been developing since 1989 the key technologies for the next generation high efficiency gas turbine of a 1,500°C class of firing temperature.

The aim is to achieve over 55% (LHV) thermal efficiency in a LNG comhined cycle power plant.

In this research, Tohoku Electric Power Company have developed: (1) advanced cooling schemes for 1st stage vanes and blades, (2) heat resistant materials for 1st stage vanes and blades and (3) high temperature low NOx combustor, which are the key technologies required for realizing a 1,500 °C class high efficiency gas turbine with a potential for practical use.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A019. doi:10.1115/96-GT-297.
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This paper summarizes the proceedings of the 1995 workshop in San Francisco, CA on “Small Gas Turbines for Distributed Generation” and the planned winter of 1996 follow-on workshop. The working definition for distributed generation used in the workshop was modular generation (generally 1–50 MW) in various applications located on electric customers sites or near load centers in an electric grid. The workshop was sponsored by the Electric Power Research Institute (EPRI), the Gas Research Institute (GRI), the U.S. Department of Energy (DOE) and Pacific Gas and Electric (PG&E). The objectives were to:

• review historical operating experience, market trends and the current state of the art of small gas turbine based options (1–50 MW size range);

• characterize benefits, motivations, application requirements and issues of small gas turbines in distributed generation strategies amongst “stakeholders”;

• identify what further efforts, technology or otherwise, should be pursued to enhance future opportunities for small gas turbine “stakeholders’; and

• define “stakeholder” interest in future forums for coordination and discussion of improved distributed generation strategies based on small gas turbines.

The workshop was attended by over 42 electric or gas utilities, 12 independent power companies and a broad cross section of equipment suppliers. Architect and Engineers (A&E’s), Research Development and Demonstration (RD&D) programs, government organizations, international utilities and other interested parties. The total workshop attendance was over 140. Small gas turbine technologies, user case histories, operating experiences, electric and gas system requirements, distributed generation economic theory, regulatory issues and general industry perspectives were reviewed. Industry input was gathered through a formal survey and four break-out sessions on future small gas turbine user needs, market requirements and potential hurdles for distributed generation.

Presentations by suppliers and users highlighted the significant commercial operating experience with small gas turbines in numerous electric utility and non-electric utility “distributed” generation applications. The primary feedback received was that there is significant and growing market interest in distributed generation strategies based on small gas turbines options. General consensus was that small gas turbine systems using natural gas would be the technology of choice in the United States for much of the near-term distributed generation market. Most participants felt that improved gas turbine technology, applications and distributed generation benefit economic evaluation models could significantly enhance the economics of distributed generation. Over 30 utility or other users expressed support for the formation of a small gas turbine interest group and an equal number expressed interest in hosting or participating in demonstration projects. A strong interest was indicated in the need for a follow-on workshop that would be more applications focused and provide a forum for coordinating research activities. Current plans by EPRI, GRI and DOE will be to include the follow-on as part of a planned workshop on “Flexible Gas Turbine Strategies” in the fall of 1996.

Commentary by Dr. Valentin Fuster
1996;():V004T10A020. doi:10.1115/96-GT-298.
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This paper will examine the performance enhancement and cost benefits of inlet air conditioning applied to a modern combined cycle plant at high ambients, resulting in lower electricity production costs. Site specific cases are presented to demonstrate a broad range of application and cost benefits.

The successful project in today’s aggressive competitive power marketplace is most typically defined as “lowest $/kW”. Traditional combined cycle plants have been driven to higher levels of efficiency by increasing gas turbine heat recovery using large, multiple pressure level heat recovery steam generators and improving heat sink technologies with aggressive cooling towers or air cooled condensers. This methodology rapidly produced less competitive results as the price of new generation was reduced.

The driving technology behind this change was the development of high output, high efficiency advanced gas turbines. Improved metallurgy, cooling schemes and blade coating systems permitted each GT manufacturer to offer improved output and efficiencies. These improvements, coupled with industry uncertainty due to the threat of deregulation and consequential reduction in new generation opportunities, has allowed new performance standards to be realized for equal or lower unit prices, leading to an unparalleled reduction of installed cost for new power plants.

Commentary by Dr. Valentin Fuster
1996;():V004T10A021. doi:10.1115/96-GT-314.
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The 701G1 50Hz Combustion Turbine continues a long line of large heavy-duty single-shaft combustion turbines by combining the proven efficient and reliable concepts of the 501F and 701F. The output of the 701G1 is 255MW with combined cycle net efficiency of over 57%. A pan of component development was conducted under the joint development program with Tohoku Electric Power Co., Inc. and a part of the design work was carried out under the cooperation with Westinghouse Electric Corporation in the U.S.A. and Fiat Avio in Italy.

This gas turbine is going to be installed to “Higashi Niigata Power Plants NO.4” of Tohoku Electric Power Co., Inc. in Japan. This plant will begin commercial operation in 1999.

This paper describes some design results and new technologies in designing and developing this next generation 1500°C class advanced gas turbine.

Commentary by Dr. Valentin Fuster
1996;():V004T10A022. doi:10.1115/96-GT-315.
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The 60Hz, 165MW gas turbine GT24 and the 50Hz, 240MW gas turbine GT26 are the first two members of ABB’s Sequential Combustion System gas turbine family. These turbines are designed to offer increased output at up to 4% efficiency advantage over today’s engines. Whereas the first combustor is based on the proven EV-combustor technology, an extensive research and development program has been carried out in developing the lean premixed, self-igniting second combustor.

This paper reports the basic research work concerning the lean premixing burners with self-ignition. The development of the burner and the combustor was based on wind tunnel and water channel experiments, CFD-calculations and combustion tests at atmospheric and high pressure.

Moreover an innovative cooling technology was developed to fullfill all conditions of the self-igniting premix combustor requiring minimal cooling air consumption. Special attention was paid both to a low sensitivity of the cooling effectiveness to variations of the imposed boundary conditions and to a robust hardware construction.

Tests of real engine parts at real engine conditions will be demonstrated in detail. Finally the paper demonstrates the potential of the sequential combustion system to reach single digit NOx levels by unveiling the results of the extensive testing program.

Commentary by Dr. Valentin Fuster
1996;():V004T10A023. doi:10.1115/96-GT-393.
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With or without turbine blade cooling, gas turbine cycles have consistently higher turbine inlet temperatures than steam turbine cycles. But this advantage is more than offset by the excessive compressor work induced by warm inlet temperatures, particularly during operation on hot summer days. Instead of seeking still higher turbine inlet temperatures by means of sophisticated blade cooling technology and high temperature-resistant blade materials, it is proposed to greatly increase the cycle net work and also improve thermal efficiency by decreasing the compressor work. This is obtained by using refrigerated inlet air and compressor intercooling to an extent which optimizes the refrigerated air inlet temperature and consequently the gas turbine compression ratio with respect to maximum specific net power.

The cost effectiveness of this conceptual cycle, which also includes regeneration, has not been examined in this paper as it requires unusually high pressure ratio gas turbines and compressors, as well as high volumetric air flow rate and low temperature refrigeration equipment for which reliable cost data is not easily available.

Commentary by Dr. Valentin Fuster
1996;():V004T10A024. doi:10.1115/96-GT-394.
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Most modern plants offer a variety of control methods which can be used one-by-one or in combination. For instance, in case of CC plants, control methods can comprise e. g. fuel control, adjustable compressor guide vanes and various feed preheat options. For the actual part-load operation the knowledge of optimum combinations is of great interest.

A computer code based on standard mathematical optimization tools for large non-linear systems of equations has been developed and tested on various gas-turbine and CC power plant configurations. The code can be employed to plants of almost any level of complexity and to any particular plant layout.

The range of control action is always limited by technological constraints imposed by mechanical, thermal, chemical or other limits and prescribed by the equipment manufacturer. The optimization code has been devised to respect an arbitrary number of such conditions as e. g. flue gas temperature, steam turbine moisture, gas turbine exit temperature and the like.

Such limits and operating instructions concerning the observance of certain parameter ranges (e. g. limits prescribed for sake of life-cycle extension) can be introduced into the optimization procedure.

Commentary by Dr. Valentin Fuster
1996;():V004T10A025. doi:10.1115/96-GT-395.
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This paper proposes the application of a modular approach to off-design prediction of multi- and single-shaft gas turbines. The performance effects of some variations of plant configurations are easy to predict. A solution adopted for module matching is shown, and the instability phenomena in some elementary units (i.e. stalling and surge in the compressor) are studied.

The partial load behavior study of aeroderivative gas turbines is presented and performance comparisons are made with a particular heavy-duty advanced application. An analysis example shows some reheat effects in combined power plant applications.

This work enabled the authors to make interesting observations on control techniques and gas-turbine configurations for advanced, combined power-plants. It also shows the wide possibilities of code applications.

Commentary by Dr. Valentin Fuster
1996;():V004T10A026. doi:10.1115/96-GT-413.
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Combined cycle cogeneration plants offer significant advantages over other cogeneration systems in many medium and large scale industrial applications. This paper presents a new methodology for the identification of the most efficient plant to satisfy given process requirements of heat and power loads and process steam conditions.

Commentary by Dr. Valentin Fuster
1996;():V004T10A027. doi:10.1115/96-GT-416.
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Power and heat rate, and exhaust gas and noise emissions are commonly used to evaluate the performance of power generation equipment. Recently, reliability, availability and maintainability (RAM) are being widely adopted as more significant evaluation criteria for gas turbine power plants. All the criteria are used to evaluate new equipment and the measurements on previous installations are the basis for expected values. What differentiates RAM from the other three criteria is the duration of the measurements. Collecting and processing of RAM data is different since it needs to be collected during normal operation of the plant and over a long period of time. This means it is a coordinated effort of both partners; the customers and the manufacturers.

This paper provides a summary of results over a period of four years with a review of the data and conclusions concerning the actual operation. It shows that gas turbine plants can be operated with high reliability and availability requirements. Outages can be reduced in both frequency and length, if the service management is based on the shared information of a worldwide RAM field data collection. A coordinated communication line is a prerequisite for sharing this information. The exchange of information is also mandatory if short reaction time for improvements is required. The planning for the implementation of the communication tools is presented in detail in terms of a ‘road map’ of this program.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A028. doi:10.1115/96-GT-424.
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The current paper describes the repowering of an existing coal plant (Rheinhafen Power Station). In this power plant, the hard coat boiler was repleced by a modern once through, Heat Recovery Steam Generator (HRSG). The HRSG is connected to a natural gas or oil fired gas turbine ABB GT26. The plant is located in Karlsruhe, Germany, and is operated by the Badenwerk AG, a public utility. The original hard coal fired plant was put into service in 1964. It is equipped with a steam turbine of approx. 100 MW power output. To maintain the initial steam data of the power plant at 160 bar and 540 °C, and to guarantee a low start-up time, an unfired once through type steam generator was chosen. Minor modifications were done in the steam turbine to increase the maximum steam turbine power output to approx. 124 MW. Combined with the approx. 240 MW power output of the GT26 a total output of 363.5 MW. MW is expected. The efficiency has thus been increased from 38 % for the steam power plant to 58.2% for the combined cycle.

Commentary by Dr. Valentin Fuster
1996;():V004T10A029. doi:10.1115/96-GT-425.
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Mitsubishi Heavy industries Ltd. developed a new high efficiency medium-size (25–35MW) gas turbine MF-221 to be used in a cogeneration plant. This gas turbine is an upscaled design of the MF-111 model, which has accumulated an operation experience of more than 1,020,000hrs. The improvement of performance and reliability was made possible by technology transfer from the latest 501F/701F gas turbine with respect to compressor and turbine aerodynamics, materials, coating and turbine cooling technology.

The MF-221 has a base load rating of 30MW at 1250°C turbine inlet temperature. Its thermal efficiency is 32% and 45% for simple and combined cycle application, respectively. It consists of a single shaft, 17-stage axial compressor, 10 can-type combustors and a 3-stage axial turbine. The prototype engine has been tested in a full-load test facility at Takasago Machinery Works to confirm the efficiency and the reliability of all parts exposed to high temperatures.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1996;():V004T10A030. doi:10.1115/96-GT-497.
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Natural gas fired combined cycle power plants now take a substantial share of the power generation market, mainly because they can be delivering power with a remarkable efficiency shortly after the decision to install is taken, and because they are a relatively low capital cost option.

The power generation markets becoming more and more competitive in terms of the cost of electricity, the trend is to go for high performance equipments, notably as far as the gas turbine and the heat recovery steam generator are concerned.

The heat recovery steam generator is the essential link in the combined cycle plant, and should be optimized with respect to the cost of electricity. This asks for a techno-economic optimization with an objective function which comprises both the plant efficiency and the initial investment.

This paper applies on an example the incremental cost method, which allows to optimize parameters like the pinch points and the superheat temperatures. The influence of the plant load duty on this optimization is emphasized. This is essential, because the load factor will not usually remain constant during the plant life-time. The example which is presented shows the influence of the load factor, which is important, as the plant goes down in merit order with time, following the introduction of more modern, more efficient power plants on the same grid.

Commentary by Dr. Valentin Fuster
1996;():V004T10A031. doi:10.1115/96-GT-516.
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A cost estimate method is presented, which enables to compare inlet air cooling system for power enhancement of combustion turbine with other power generation system. A new energy conversion index is developed which arranges system design parameters in a dimensionless form and also exhibits running cost. It is suggested that the inlet air cooling system is equivalent to simple cycle or pumped storage in view of the dimensionless running cost. Next, a cost diagram relating capital cost to power generation cost is presented also in non-dimensional form, which could provide a measure to examine investment worth for a power producer. Moreover, cooling effectiveness as function of cooled inlet air temperature is investigated using specific thermal energy. It is revealed that cooling beyond dew point requires a larger thermal energy per electric energy produced and thus less economical unless the price of electricity depends on electricity demand.

Commentary by Dr. Valentin Fuster
1996;():V004T10A032. doi:10.1115/96-GT-517.
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The newly developed depth-loading filter types MaxiPleat filter and depth-loading filter cartridge offer gas turbine users numerous advantages in terms of clean air quality in the combustion air, cost-efficiency due to favourable pressure drop, long life and high functional reliability over the entire operating period.

The MaxiPleat filters fitted with a paper-like filter medium are produced by using the patented thermal embossing process, distinctive for its solution to the spacing problem. Without using any foreign materials as separators, depths of 250 mm can be achieved in pleating, with V-shaped, flow-optimized pleat geometries. This ensures low pressure drops and high dust holding capacities.

The depth-loading filter cartridge is intended as a replacement filter for surface-loading filter cartridges given unsatisfactory results. A conventional pulse-jet system can be converted to a depth-loading filter without any expensive modification. The depth-loading filter cartridge extends substantially the useful life of the filters and significantly improves the pressure drop characteristics, especially when sticky dusts and high humidity locations are involved.

Commentary by Dr. Valentin Fuster
1996;():V004T10A033. doi:10.1115/96-GT-530.
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Much of the steam-turbine based, power generating units all over the word are more than 30 years old now. Within a few years they will face the possibility of retirement from service and replacement. Nonetheless some of them are firm candidates for repowering, a technology able to improve plant efficiency, output and reliability at low costs.

This paper summarizes a study performed to establish the feasibility to repower a 2 × 33 MW steam turbine power plant and the procedure followed until selection of the steam cycle more suitable to the project. The preferred solution is compared with direct replacement of the units by a new combined cycle.

Various repowering options were reviewed to find “beat recovery” type repowering as the best solution. That well-known technology consists of replacing the steam generator by a gas turbine coupled to an HRSG, supplying steam to the existing steam turbine.

Three “GT+HRSG+ST” arrangements were considered. Available gas turbine-generators — both industrial and aero-derivative type —, were surveyed for three power output ranges. Five “typical” gas turbine-generator classes were then selected.

Steam flow raised at the HRSG, gross and net power generation, and heat exchanging surface area of the HRSG, were calculated for a broad range of usually applied, steam turbine throttle conditions. Both single pressure and double pressure steam cycles were considered, as well as supplemental fire and convenience of utilizing the existing feed water heaters. Balance of plant constraints were also reviewed.

Estimates were developed for total investment, O&M costs, fuel expenses, and revenues. Results are shown through various graphics and tables. The route leading to the preferred solution is explained and a sensitivity analysis added to validate the selection.

The preferred solution, consisting in a Class 130 gas turbine in arrangement 1–1–2, a dual-pressure HRSG and a steam cycle without feed-water heaters, win allow delivering 200 MW to the grid, with a heat rate of 7423 kJ/kW-hr. Investment was valued at $MM77.0, with an IRR of 15.3%. Those figures compare well with the option of installing a new GTCC unit: with a better heat rate but an investment valued at $MM97.5, its IRR will only be 12.4%.

Commentary by Dr. Valentin Fuster
1996;():V004T10A034. doi:10.1115/96-GT-536.
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When a gas enclosed in a cavity is heated or cooled, its pressure changes with its temperature as well. If a set of two countermoving “driven” cavity cascades employs the same free wall, then the system will operate as a countercurrent heat exchanger. At the exit points of the heat exchanger the two gases can be brought back to their original (atmospheric) pressure by isentropic processes thus producing useful work. The entire set of thermodynamic processes forms a double Lenoir cycle. The exhausts from the two Lenoir cycles may drive two more sets of corresponding cycles, thus allowing for the cascading of the process, until the added useful work becomes insignificant. When this idea is employed as a bottoming cycle in a Gas Turbine lead Combined cycle, employing four sets of Lenoir cycles, the achievable total thermal efficiencies rise to the 75 to 82 % level, athough the amount of heat transferred in all these processes is about 50 % more than that in a modern Brayton-Rankine combined cycle.

Commentary by Dr. Valentin Fuster
1996;():V004T10A035. doi:10.1115/96-GT-538.
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Among cogeneration facilities block heating stations and large combined cycle plants are two extreme examples of district heating technologies. In this paper, these two alternatives will be applied to one and the same representative district heating task. The thermodynamic differences will be made clear and the advantages of heating by extracting steam from a combined cycle plant will become evident. An important conclusion from an engineering point of view is that extracting heat from a combined cycle plant should be considered even if this plant is located at greater distances from the heat consumers.

Commentary by Dr. Valentin Fuster

Industrial and Cogeneration

1996;():V004T11A001. doi:10.1115/96-GT-217.
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The 6 MW class Allison 501-KH gas turbine was introduced to the industrial power generation market in the mid-1980s as a low risk modification of the 501-KB engine. The aero-derivative and industrial background of the 501-KB engine is discussed along with the 501-KH product definition and product description. The results of the development, and production 501-KH engines are presented, including performance testing and customer operation. In addition, near term improvement plans for the 501-KH and a boosted version are outlined.

Commentary by Dr. Valentin Fuster
1996;():V004T11A002. doi:10.1115/96-GT-230.
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‘Soft’ start flow distribution, control capability, sealing performance, and safety, were four reasons Oklahoma Municipal Power Authority (OMPA), in cooperation with Black & Veatch and Vogt, installed Dual BiPlane Heat Recovery Steam Generator (HRSG) Isolation and Bypass Dampers from Damper Design, Inc. on the gas turbine outlet at this facility.

The DDI BiPlane damper is truly a unique damper for this application. This design allowed OMPA to have the safety and isolation of a flap diverter white providing the even gas distribution and accurate flow control to the HRSG under startup conditions available from a louver style damper.

The arrangement consists of two DDI BiPlane dampers, one on the inlet to the HRSG and one isolating the stack. Since safety is highest priority, Damper Design utilized an independent lockout type linkage that allows control of the dampers while positively preventing the closure of both gas paths at the same time.

By installing the DDI BiPlane damper, OMPA has the ability to throttle the gas turbine exhaust flow independently to the HRSG and stack. This allows the gases to enter the HRSG with a much more evenly distributed flow pattern and at lower controlled flow rates than with competing designs.

This paper will address the benefits, design, and operating advantages of the use of the DDI BiPlane Damper specifically in HRSG isolation and bypass installations. It is also applicable to other systems where control and isolation with one damper is desirable.

Commentary by Dr. Valentin Fuster
1996;():V004T11A003. doi:10.1115/96-GT-277.
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A modular software system was developed to optimize thermodynamic and financial operation of the 350 MW Selkirk Cogen combined cycle power plant. The package is derived from commercially available modeling software, customized for this site. The system satisfies the information needs of both technical and business oriented personnel by: (1) direct simulation utilizing the simulator’s detailed, accurate, component-wise models and (2) lookup into a large database of pre-simulated plant scenarios which obey an established operating methodology. An unattended on-line module, with access to the distributed control system, continually compares simulator output with plant measurements. This provides measures of instrumentation health and current equipment performance indicators which are fed back to update the pre-simulated database. A series of example uses of the software is provided.

Commentary by Dr. Valentin Fuster
1996;():V004T11A004. doi:10.1115/96-GT-301.
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Biomass fuelled combined cycle with gas turbine for co-generation, has the promise of being able to produce electricity at competitive cost. The sugar cane industries in the developing countries are targets for near term-applications of this technology.

Different options for increasing the electricity generation in the sugar mills by using more advanced steam process and combined cycle technology, using cane trash and bagasse as a fuel for has been analyzed. The TPC sugar mill in Tanzania was selected as a case study for investigation. Introduction of a combined gas turbine/steam turbine process will make it possible to increase the electricity output from 2.5 MW to 30 MW at this plant during milling season. By using cane trash as fuel during the off-season period, the electricity generation can be increased by a factor of 20 compared to what is generated at TPC sugar factory today.

The financial evaluation indicated that the annual profit would range from US$ 3.5 million for the advanced steam process with 6.5 years pay-back time, to be US$ 4.7 million for the combined gas turbine/steam turbine process with 6.8 years pay-back time.

Commentary by Dr. Valentin Fuster
1996;():V004T11A005. doi:10.1115/96-GT-302.
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A general method capable to solve optimization power plant problems simultaneously with the solution of equations describing the plant behavior is discussed.

The method has been implemented into CGSPO code whose main features as the plant modular structure and its automatic assembling are described.

Procedures foreseen in the code are: cycle calculations, sizing of components and off-design analysis. Examples showing the capabilities and the flexibility of the method are given.

The code is suitable for the analysis of plant including commercially available machines whose modifications to match with other components may be investigated.

Topics: Power stations
Commentary by Dr. Valentin Fuster
1996;():V004T11A006. doi:10.1115/96-GT-331.
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Steam injection has been employed in gas turbines for over twenty-five years for power increase (more than 50% on some gas turbines) and efficiency improvements (more than 20%). For further improvement of efficiency on steam injected gas turbine, Partial Regenerative Steam Injected Gas Turbine was studied.

Cycle analysis was carried out for the evaluation of efficiency among three systems, Steam Injected Gas Turbine, Regenerative Steam Injected Gas Turbine and Partial Regenerative Steam Injected Gas Turbine. Results of the analysis show that Partial Regenerative Steam Injected Gas Turbine can realize higher efficiency than other two systems.

In addition to the cycle analysis, the effect of applying the concept of Partial Regenerative Steam Injected Gas Turbine to the actual engine Allison gas turbine model 501-KH was evaluated. And the effect of integrating compressor inter-cooling process in Partial Regenerative Steam Injected Gas Turbine was also evaluated.

Topics: Gas turbines , Steam
Commentary by Dr. Valentin Fuster
1996;():V004T11A007. doi:10.1115/96-GT-332.
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In the paper the dynamic non-linear model of single shaft industrial gas turbine was developed as the first stage of a methodology aimed at the diagnosis of measurement and control sensors and gas turbine operating conditions.

The model was calibrated by means of reference steady-state condition data of a real industrial gas turbine and was used to simulate various machine transients.

The model is modular in structure and was carried out in simplified form, but not so as to compromise its accuracy, to reduce the calculation time and thus make it more suitable for on-line simulation.

The comparison between values of working parameters obtained by the simulations and measurements during some transients on the gas turbine in operation provided encouraging results.

Commentary by Dr. Valentin Fuster
1996;():V004T11A008. doi:10.1115/96-GT-333.
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The authors present the application of a method for gas turbine analysis, that they have recently introduced, based upon the selection of rotating components and on the study of off-design behaviour. The paper deals with an aero-derivative gas turbine, whose operating field is evaluated by an advanced cycle calculation which takes into account the fluid-dynamic and mechanical matching of the turbomachines.

Different regulation systems are considered, like variable-geometry compressor and turbine vanes, whose effect is combined with the variations in rotational speed of the gas generator device.

The simulation model allows definition of a performance map of the gas turbine, not only in terms of mechanical output and efficiency but also of pollutant emissions, as a result of the prediction of thermal NO formation inside the combustor.

The method leads to the establishment of an optimal control and regulation strategy with respect to a prescribed objective, i.e., either for maximum in energy saving or for the best compromise between performance and emission levels. Cases are examined with reference to both mechanical energy production and combined heat and power generation.

Commentary by Dr. Valentin Fuster
1996;():V004T11A009. doi:10.1115/96-GT-384.
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This paper, is concerned with the evaluation of economic and energy saving characteristics of a super waste incineration cogeneration plant, which is equipped with gas turbines as topping cycle to overcome a drawback of low power generating efficiency of conventional waste incineration cogeneration plants only with steam turbines. Economic and energy saving characteristics are evaluated using an optimal planning method which determines capacities and operational strategies of constituent equipment from their many alternatives so as to minimize the annual total cost. Through a case study, advantages of a super waste incineration cogeneration plant are shown in comparison with a conventional one. A parametric study is also carried out with respect to the amounts of waste collected and energy distributed.

Commentary by Dr. Valentin Fuster
1996;():V004T11A010. doi:10.1115/96-GT-434.
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A design point study of a semi-closed recuperated intercooled gas turbine combined with a closed, unfired, Rankine cycle is presented to demonstrate the overall thermodynamic design and efficiency tradeoffs for this type of cycle. Through its semi-closed design, having control over combustor equivalence ratio and recirculation flow exit pressure, this cycle provides improvements in emissions, specific power (net system power output divided by gas turbine inlet airflow), part power thermal efficiency, and overall system size relative to a combined cycle with an open cycle gas turbine. The relationship of design variables to cycle and component selection is discussed. Interface heat exchanger configuration, along with bottoming cycle choices of regeneration, feedwater heating, and fluid (H2O or DOWTHERM®A) are evaluated to determine their effects on mechanical design and thermal efficiency.

Topics: Design , Gas turbines , Cycles
Commentary by Dr. Valentin Fuster
1996;():V004T11A011. doi:10.1115/96-GT-535.
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The full mapping of a new gas turbine axial compressor at different speeds, IGV settings and pressure ratios (from choking to surge) has been performed utilizing a complete gas turbine with a suitable set of modifications.

The main additions and modifications, necessary to transform the turbine into the Compressor Test Vehicle (CTV), are:

- Compressor inlet throttling valve addition

- Compressor discharge bleed valve addition

- Turbine 1st stage nozzle area reduction

- Starting engine change (increase in output and speed range).

This method has been successfully employed on two different single shaft heavy-duty gas turbines (with a power rating of 11MW and 170 MW respectively).

The paper describes the theoretical basis of this testing method and a specific application with the above mentioned 170 MW machine.

Commentary by Dr. Valentin Fuster

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