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Heat Transfer

1994;():V004T09A001. doi:10.1115/94-GT-001.
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The local heal transfer inside the entrance to large scale models of film cooling holes has been measured using the transient heat transfer technique. The method employs temperature sensitive liquid crystals to measure the surface temperature of large scale perspex models. Full distributions of local Nusselt number were calculated based on the cooling passage centreline gas temperature ahead of the cooling hole. The circumferentially averaged Nusselt number was also calculated based on the local mixed bulk driving gas temperature to aid interpretation of the results, and to broaden the potential application of the data. Data are presented for a single film cooling hole inclined at 90 and 150 degrees to the coolant duct wall. Both holes exhibited entry length heat transfer levels which were significantly lower than those predicted by entry length data in the presence of crossflow. The reasons for the comparative reduction are discussed in terms of the interpreted flow field.

Commentary by Dr. Valentin Fuster
1994;():V004T09A002. doi:10.1115/94-GT-002.
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Experiments have been conducted on a large model of a turbine blade. Attention has been focussed on the leading edge region, which has a semi-circular shape and four rows of film cooling holes positioned symmetrically about the stagnation line. The cooling holes were oriented in a spanwise direction with an inclination of 30° to the surface, and had streamwise locations of ±15° and ±44° from the stagnation line. Film cooling effectiveness was measured using a heat/mass analogy. Single row cooling from the holes at 15° and 44° showed similar patterns: spanwise averaged effectiveness which rises from zero at zero coolant mass flow to a maximum value η* at some value of mass flow ratio M*, then drops to low values of η at higher M. The trends can be quantitatively explained from simple momentum considerations for either air or CO2 as the coolant gas. Close to the holes, air provides higher η values for small M. At higher M, particularly farther downstream, the CO2 may be superior. The use of an appropriately defined momentum ratio G collapses the data from both holes using either CO2 or air as coolant onto a single curve. For η*, the value of G for all data is about 0.1. Double row cooling with air as coolant shows that the relative stagger of the two rows is an important parameter. Holes in line with each other in successive rows can provide improvements in spanwise averaged film cooling effectiveness of as much as 100% over the common staggered arrangement. This improvement is due to the interaction between coolant from rows one and two, which tends to provide complete coverage of the downstream surface when the rows are placed correctly with respect to each other.

Commentary by Dr. Valentin Fuster
1994;():V004T09A003. doi:10.1115/94-GT-014.
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Three-dimensional Navier-Stokes calculations have been performed on various geometries in the presence of discrete-hole injection. The quality of the aerodynamic and thermal predictions of the flow is assessed by comparison to experiments.

The code used for the calculations is developed at ONERA and has previously been presented by various authors (Billonnet et al., 1992). It solves the unsteady set of three-dimensional Navier-Stokes equations, completed by a mixing-length turbulence model, using a finite volume technique.

The multi-domain approach of the code has facilitated the treatment of this type of geometry. The injection holes are discretized on cylindrical subdomains which overlap the mesh of the main flow.

Two applications of the code are presented in this paper. First, a calculation was performed on a row of hot jets injected into a flat plate turbulent boundary layer. Secondly, the code was tested on a plane nozzle guide vane grid with multiple injections. Heat transfer rates, temperature and velocity profiles are compared to experimental data.

Commentary by Dr. Valentin Fuster
1994;():V004T09A004. doi:10.1115/94-GT-015.
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A numerical investigation of film cooling on a turbine rotor blade has been carried out. The computations were performed with a 3D-Navier-Stokes code utilizing an unstructured solution adaptive grid methodology (Dawes (1992)). The code uses a low Reynolds number k-epsilon model for prescribing the Reynolds stresses. The results show that there is a significant interaction between the coolant flow and the secondary flow near the hub and the tip of the turbine blade. It was observed that, by blowing on the pressure side of the blade, some of the cooling air was transported through the tip gap of the blade to the suction side of the blade where the coolant flow interacts with the secondary flow field.

When radial inlet temperature distortion (RTD) is included, it was possible to show that there were some further modifications of the film cooling effectiveness on the rotating blade near the pressure side tip. This is believed to be mostly because of the changed secondary flow system due to the radial inlet temperature profile.

Commentary by Dr. Valentin Fuster
1994;():V004T09A005. doi:10.1115/94-GT-016.
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A three-dimensional Navier-Stokes analysis tool has been developed In order to study the effect of film cooling on the flow and heat transfer characteristics of actual turbine airfoils. An existing code (Amone et al., 1991) has been modified for the purpose. The code is an explicit, multigrid, ceil-centered, finite volume code with an algebraic turbulence model. Eigenvalue scaled artificial dissipation and variable-coefficient implicit residual smoothing are used with a full-multigrid technique. Moreover, Mayle’s transition criterion (Mayle, 1991) is used. The effects of film cooling have been incorporated into the code in the form of appropriate boundary conditions at the hole locations on the airfoil surface. Each hole exit is represented by several control volumes, thus providing an ability to study the effect of hole shape on the film-cooling characteristics. Comparison with mid-span experimental data for four and nine rows of cooling holes is fair. The computations, however, show a strong spanwise variation of the heat transfer coefficient on the airfoil surface, specially when the shower-head cooling holes are on.

Commentary by Dr. Valentin Fuster
1994;():V004T09A006. doi:10.1115/94-GT-018.
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The leading edge of a turbine blade was simulated as a circular cylindrical surface. The effect of free-stream turbulence on the mass transfer upstream edge of the injection hole normal to the cylindrical surface has been investigated by using a naphthalene sublimation technique. The effects of injection location, blowing ratio on the Sherwood number distribution were examined as well. The free-stream Reynolds number based on the cylinder diameter is 53,000 and other conditions investigated are: free-stream turbulence intensities of 0.5%, 3.9% and 8.0%, injection locations of 40, 50 and 60 degrees from the front stagnation point of the cylinder, and blowing ratios of 0.5 and 1.0. The role of the horseshoe vortex formed upstream edge of the normally injected jet is discussed in detail. When the coolant jet is injected at 40 degrees, the mass transfer upstream of the jet is not affected by the coolant jet at all. On the other hand, when the injection hole is located beyond 50 degrees the mass transfer upstream edge of the injection hole suddenly increases due to the formation of the horseshoe vortex, but it decreases as the free-stream turbulence intensity increases because the strength of the horseshoe vortex structure is weakened. The role of the horseshoe vortex is confirmed by placing a rigid rod at the injection hole instead of issuing the jet. In the case of the rigid rod, the Sherwood number upstream of the injection hole is much larger due to the intense influence of the horseshoe vortex. The variation in the strength of the horseshoe vortex structure with free-stream turbulence intensities was observed by a flow visualization.

Commentary by Dr. Valentin Fuster
1994;():V004T09A007. doi:10.1115/94-GT-022.
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The effect of transition modeling on the heat transfer predictions from rotating turbine blades was investigated. Three-dimensional computations using a Reynolds-averaged Navier-Stokes code were performed. The code utilized the Baldwin-Lomax algebraic turbulence model which was supplemented with a simple algebraic model for transition. The heat transfer results obtained on the blade surface and the hub end wall were compared with experimental data for two Reynolds numbers and their corresponding rotational speeds. The prediction of heat transfer on the blade surfaces was found to improve with the inclusion of the transition length model and wake induced transition effects over the simple abrupt transition model.

Commentary by Dr. Valentin Fuster
1994;():V004T09A008. doi:10.1115/94-GT-024.
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The effects of streamwise acceleration on a two-dimensional heated boundary layer undergoing natural laminar-turbulent transition were investigated with detailed measurements of momentum and thermal transport phenomena. Tests were conducted over a heated flat wall with zero pressure-gradient and three levels of streamwise acceleration: Display FormulaKνU¯2dU¯dx= 0.07, 0.16, and 0.25 × 10−6. Free-stream turbulence intensities were maintained at approximately 0.5% for the baseline case and 0.4% for the accelerating cases. A miniature three-wire probe was used to measure mean velocity and temperature profiles, Reynolds stresses, and Reynolds heat fluxes. Transition onset and end were inferred from Stanton numbers and skin-friction coefficients.

The results indicate that mild acceleration delays transition onset and increases transition length both in terms of distance, x1 and Reynolds number based on x. Transition onset and length are relatively insensitive to acceleration in terms of momentum thickness Reynolds number. This is supported by the boundary layer thickness and integral parameters which indicate that a favorable pressure gradient suppresses boundary layer growth and development in the transition region. Heat transfer rates and temperature profiles in the late-transition and early-turbulent regions lag behind the development of wall shear stress and velocity profiles. This lag increases as K increases, indicating that the evolution of the heat transport is slower than that of the momentum transport. Comparison of the evolution of RMS temperature fluctuations to the evolution of Reynolds normal stresses indicates a similar lag in the RMS temperature fluctuations.

Commentary by Dr. Valentin Fuster
1994;():V004T09A009. doi:10.1115/94-GT-025.
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Detailed measurements are performed about time-averaged beat transfer distributions around the leading edge of a blunt body which is affected by incoming periodic wakes from the upstream moving bars. The blunt body is a test model of a front portion of a turbine blade in gas turbines and consists of a semicircular cylindrical leading edge and a flat plate afterbody. A wide range of the steady and unsteady flow conditions are adopted as for the Reynolds number based on the diameter of the leading edge and the bar-passing Strouhal number. The measured heat transfer distributions indicate that the wakes passing over the leading edge cause significant increase in beat transfer before the separation and the higher Strouhal number results in higher heat transfer. From this experiment, a correlation for the heat transfer enhancement around the leading edge due to the periodic wakes is deduced as a function of the Stanton number and it is reviewed by comparison with the other experimental works.

Topics: Heat transfer , Wakes
Commentary by Dr. Valentin Fuster
1994;():V004T09A010. doi:10.1115/94-GT-037.
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Turbulence measurements for both momentum and heat transfer are taken in a low-velocity, turbulent boundary layer growing naturally over a concave wall. The experiments are conducted with negligible streamwise acceleration and a nominal free-stream turbulence intensity of −8%. Comparisons are made with data taken in an earlier study in the same test facility but with a 0.6% free-stream turbulence intensity. Results show that elevated free-stream turbulence intensity enhances turbulence transport quantities like uv and vt in most of the boundary layer. In contrast to the low-turbulence cases, high levels of transport of momentum are measured outside the boundary layer. Stable, Görtler-like vortices, present in the flow under low-turbulence conditions, do not form when the free-stream turbulence intensity is elevated. Turbulent Prandtl numbers, Prt, within the log region of the boundary layer over the concave wall increase with streamwise distance to values as high as 1.2. Profiles of Prt suggest that the increase in momentum transport with increased free-stream turbulence intensity precedes the increase in heat transport. Distributions of near-wall mixing length for momentum remain unchanged on the concave wall when free-stream turbulence intensity is elevated. Both for this level of free-stream turbulence and for the lower level, mixing length distributions increase linearly with distance from the wall following the standard slope. However when free-stream turbulence intensity is elevated, this linear region extends farther into the boundary layer, indicating the emerging importance of larger eddies in the wake of the boundary layer with the high-turbulence free-stream. Because these eddies are damped by the wall, the influence of the wall grows with eddy size.

Commentary by Dr. Valentin Fuster
1994;():V004T09A011. doi:10.1115/94-GT-051.
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This study investigated the adiabatic wall cooling effectiveness of a single row of film cooling boles injecting into a turbulent flat plate boundary layer below a turbulent, zero pressure gradient freestream. Levels of freestream turbulence (Tu) up to 17.4% were generated using a method which simulates conditions at a gas turbine combustor exit. Film cooling was injected from a single row of five 35 degree slant-hole injectors (length/diameter = 3.5. pitch/diameter = 3.0) at blowing ratios from 0.55 to 1.85 and at a nearly constant density ratio (coolant density/freestream density) of 0.95. Film cooling effectiveness data is presented for Tu levels ranging from 0.9% to 17% at a constant freestream Reynolds number based on injection hole diameter of 19000. Results show that elevated levels of freestream turbulence reduce film cooling effectiveness by up to 70% in the region directly downstream of the injection hole due to enhanced mixing. At the same time, high freestream turbulence also produces a 50–100% increase in film cooling effectiveness in the region between injection boles. This is due to accelerated spanwise diffusion of the cooling fluid, which also produces an earlier merger of the coolant jets from adjacent holes.

Commentary by Dr. Valentin Fuster
1994;():V004T09A012. doi:10.1115/94-GT-067.
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Film cooling performance for injection through discrete holes in the endwall of a turbine blade is investigated. The effectiveness is measured at sixty locations in the region covered by injection. Three nominal blowing rates, two density ratios, and two approaching flow Reynolds numbers are examined. Analysis of the data reveals that even sixty locations are insufficient for the determination of the field of film cooling effectiveness with its strong local variations. Visualization of the traces of the coolant jets on the endwall surface, using ammonium-diazo-paper, provides useful qualitative information for the interpretation of the measurements, revealing the paths and interaction of the jets which change with blowing rate and density ratio.

Commentary by Dr. Valentin Fuster
1994;():V004T09A013. doi:10.1115/94-GT-094.
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The flow over the high pressure blades of a gas turbine is disturbed by wakes and shock waves from the nozzle guide vanes upstream. These disturbances lead to increased heat transfer to the blade surfaces, the accurate prediction of which is an essential stage in the design process.

The Oxford Rotor experiment consists of a highly instrumented 0.5 m diameter shroudless turbine which is supplied with air from a piston tube during the 200 ms run time and simulates realistic engine Mach and Reynolds numbers. Previous experiments have measured blade surface pressures and heat transfer rates, and compared them with similar data from linear cascades.

The present work is designed to enable the accuracy of rotation terms in computational fluid dynamics (CFD) calculations to be assessed, by providing heat transfer data from the rotating frame in the absence of wakes. Flow disturbances were avoided by removing the nozzle guide vanes, the correct angle of incidence onto the rotor blades being achieved by rotating the rotor in the reverse direction. Blade surface heat fluxes were measured using thin film gauges. In the absence of the usual blade-passing fluctuations, the root-mean-square fluctuation in heat flux was typically only 7% of the DC level.

Nusselt numbers are compared with cascade data and CFD predictions from both a three-dimensional viscous Navier-Stokes equation solver and a two-dimensional boundary layer prediction. The low inlet turbulence level produced a long laminar region on the suction surface followed by sudden transition. CFD predictions of Nusselt number on this surface were very sensitive to the choice of boundary layer state, and the experimental level was approximately mid-way between predictions with a transitional intermittency distribution and those with a turbulent distribution. On the pressure surface the levels were approximately 25% below predicted levels, and possible reasons for this are considered.

Commentary by Dr. Valentin Fuster
1994;():V004T09A014. doi:10.1115/94-GT-095.
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The accurate prediction of turbine airfoil metal temperatures remains one of the critical issues in the development of high efficiency engines. Free-stream and wake-generated turbulence plays a major role in the external heat transfer of the cooled airfoils. Turbulence simulation experimental methodology has been employed to provide external heat load similarity between the engine and the elevated temperature cascade rig conditions. The methodology is based on simulation of turbulence intensity to produce equal mainstream heat transfer effects at the stagnation region of the airfoil in both engine and cascade environments. A recently completed fill-scale hot cascade facility provides a realistic simulation of an actual engine in terms of gas-side and coolant-side heat transfer. Significant attention is paid to emulating the free-stream turbulence environment of an actual engine. Indirect measurements of free-stream turbulence are performed with a custom designed calorimetric probe and heat flux probe. Well established stagnation point heat transfer correlations are used to deduce the free-stream turbulence intensity. The cascade rig provides a detailed map of local cooling effectiveness along the airfoil, which can be controlled by varying gas-side and coolant-side convective heat transfer. Results of the experimental study demonstrate the practical benefits of this methodology for more accurate evaluation of the airfoil external heat transfer, particularly when a combustor system is redefined or an engine is uprated and the airfoil cooling system has to be modified.

Commentary by Dr. Valentin Fuster
1994;():V004T09A015. doi:10.1115/94-GT-122.
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Predictions of the heat transfer rates on the hot surfaces of a turbine cascade blade passage as influenced by the turbulence models was examined. A zero equation turbulence model supplemented by a bypass transition model and a two equation low Reynolds number model were chosen for this study. The experimental data of Graziani et. al. were used for comparison. The comparisons suggest that at least for the experimental data considered in this work the use of a two-equation model does not provide an overall more accurate solution than the zero equation model. This conclusion is strengthened if one takes into account the relative economy of computations with the algebraic model.

Commentary by Dr. Valentin Fuster
1994;():V004T09A016. doi:10.1115/94-GT-123.
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The effect of five different C type grid geometries on the predicted heat transfer and aerodynamic performance of a turbine stator is examined. Predictions were obtained using two flow analysis codes. One was a finite difference analysis, and the other was a finite volume analysis. Differences among the grids in terms of heat transfer and overall performance were small. The most significant difference among the five grids occurred in the prediction of pitchwise variation in total pressure. There was consistency between results obtained with each of the flow analysis codes when the same grid was used. A grid generating procedure in which the viscous grid is embedded within an inviscid type grid resulted in the best overall performance.

Commentary by Dr. Valentin Fuster
1994;():V004T09A017. doi:10.1115/94-GT-162.
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Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system.

The objective of this experimental investigation was to conduct a series of thirteen tests to measure the rib surface-averaged heat transfer coefficient, in a square duct roughened with staggered 90° ribs. To investigate the effects that blockage ratio, e/Dh, and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133. 0.167 and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5 and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hflor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared.

It is concluded that:

1) the rib average heat transfer coefficient is much higher than that for the area between the ribs,

2) similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio,

3) a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested,

4) under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the mid-channel positions,

5) the upstream-most rib average heat transfer coefficients decreased with the blockage ratio, and

6) thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

Commentary by Dr. Valentin Fuster
1994;():V004T09A018. doi:10.1115/94-GT-163.
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Experimental investigations have shown that the enhancement in heat transfer coefficients for air flow in a channel roughened with angled ribs is on the average higher than that roughened with 90° ribs of the same geometry. Secondary flows generated by the angled ribs are believed to be responsible for these higher heat transfer coefficients. These secondary flows also create a spanwise variation in heat transfer coefficient on the roughened wall with high levels of heat transfer coefficient at one end of the rib and low levels at the other end. In an effort to basically double the area of high heat transfer coefficients, the angled rib is broken at the center to form a V-shape rib and tests are conducted to investigate the resulting heat transfer coefficients and friction factors. Three different square rib geometries, corresponding to blockage ratios of 0.083, 0.125 and 0.167, with a fixed pitch-to-height ratio of 10, mounted on two opposite walls of a square channel in a staggered configuration are tested in a stationary channel for 5000 < Re < 30000. Heat transfer coefficients, friction factors and thermal performances are compared with those of 90°, 45° and discrete angled ribs. The V-shape ribs are tested for both pointing upstream and downstream of the main flow. Test results show that:

a) 90° ribs represent the lowest thermal performance, based on the same pumping power, and is essentially the same for the 2:1 change in blockage ratio, b) low blockage ratio (e/Dh =0.083) V-shape ribs pointing downstream produced the highest heat transfer enhancement and friction factors. Amongst all other geometries with blockage ratios of 0.125 and 0.167, 45° ribs showed the highest heat transfer enhancements with friction factors less than those of V-shape ribs, c) thermal performance of 45° ribs and the lowest blockage discrete ribs are among the highest of the geometries tested in this investigation, and, d) discrete angled ribs, although inferior to 45° and V-shape ribs, produce much higher heat transfer coefficients and lower friction factors compared to 90° ribs.

Commentary by Dr. Valentin Fuster
1994;():V004T09A019. doi:10.1115/94-GT-164.
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Using an analog mass transfer system based on naphthalene sublimation, the present research focuses on investigating the local heat transfer characteristics from three-pass smooth and turbulated blade cooling passages. To simulate the actual passage geometry, the test model is incorporated with trapezoidal cross-sections including variable passage sizes. Measured local mass transfer results reveal strong evidence of velocity re-distribution over the trapezoidal flow area. Elevated mass transfer always exists in the vicinity of a sharp turn. However, in the present study, one of the most notable mass transfer increases is perceived in the third pass, downstream to the second turn, where the flow area is reduced severely. Overall, the combined effects of the three-pass and two sharp turns virtually doubles the mass transfer as compared to its straight counterpart with fully developed, turbulent flow. With a pitch-to-height ratio equal to 10 and 90-degree orientation, the rib turbulators produce approximately an additional 30% of overall mass transfer enhancement in comparison to the smooth case. Locally, rib-induced enhancement varies with different surfaces and passes. The greatest enhancement lies on the first pass, about 40%; the other two passes are comparable, less than 20%.

Commentary by Dr. Valentin Fuster
1994;():V004T09A020. doi:10.1115/94-GT-165.
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A naphthalene sublimation technique is used to investigate convective transport from a simulated turbine blade in a stationary linear cascade. In some of the tests undertaken a trip wire is stretched along the span of the blade near the leading edge. The disturbance produced by tripping the boundary layers on the blade near the leading edge causes early boundary layer transition, creates high mass transfer rate on the pressure side and in the laminar flow region on the suction side, but lowers the transfer rate in the turbulent flow region on the suction side. Comparison is made with other heat and mass transfer studies in the two dimensional region far from the endwall and good agreement is found.

Near the endwall, flow visualization indicates a strong secondary flow pattern. The impact of vortices initiated near the endwall on the laminar-turbulent transition extends three dimensional effects to about 0.8 chord lengths on the suction side and to about 0.2 chord lengths on the pressure side away from the endwall. The effect of the passage vortex and the new vortex induced by the passage vortex on mass transfer is clearly seen and can be traced along the suction surface of the blade. Close to the endwall the highest mass transfer rate on the suction surface is not found near the leading edge. It occurs at about 27% of the curvilinear distance from the stagnation line to the trailing edge where a strong main flow and the secondary passage flow from the pressure side of the adjacent blade interact. The influences of some small but very intense corner vortices and the passage vortex on mass transfer are also observed on both surfaces of the blade.

Commentary by Dr. Valentin Fuster
1994;():V004T09A021. doi:10.1115/94-GT-166.
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Measurements are presented of the streamwise velocity variation within a laminar boundary layer on a concave surface of 4 m radius of curvature for which the free-stream velocity gradient factor Display Formulaν/U02dU0/dx was approximately 1 × 10−6. The velocity variation was consistent with the presence of counter-rotating vortices resulting from the Görtler instability. The vortices exhibited exponential growth over the streamwise extent of the measurements to a disturbance amplitude of approximately 13% of the local freestream velocity. The vortex growth rates were found to be less than those for a zero velocity gradient factor indicating that a favorable pressure gradient stabilizes the flow with respect to the Görtler instability.

Boundary layer profiles at local upwash and downwash positions are compared with the linear theory for which the mean flow was modelled using the Pohlhausen approximation to the solution of the boundary layer equations. The agreement between the measured and predicted profiles indicates that the linear stability theory can provide a fair approximation to the small amplitude growth of the Görtler instability.

Commentary by Dr. Valentin Fuster
1994;():V004T09A022. doi:10.1115/94-GT-167.
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The clearance gap between the stationary outer air seal and blade tips of an axial turbine allows a clearance gap leakage flow to be driven through the gap by the pressure-to-suction side pressure difference. The presence of strong secondary flows on the pressure side of the airfoil tends to deliver air from the hottest regions of the mainstream to the clearance gap. The blade tip region, particularly near the trailing edge, is very difficult to cool adequately with blade internal coolant flow. In this case, film cooling injection directly onto the blade tip region can be used in an attempt to directly reduce the heat transfer rates from the hot gases in the clearance gap to the blade tip. The present paper is intended as a memorial tribute to the late Professor Darryl E. Metzger who has made significant contributions in this particular area over the past decade. A summary of this work is made to present the results of his more recent experimental work that has been performed to investigate the effects of film coolant injection on convection heat transfer to the turbine blade tip for a variety of tip shapes and coolant injection configurations. Experiments are conducted with blade tip models that are stationary relative to the simulated outer air seal based on the result of earlier works that found the leakage flow to be mainly a pressure-driven flow which is related strongly to the airfoil pressure loading distribution and only weakly, if at all, to the relative motion between blade tip and shroud. Both heat transfer and film effectiveness are measured locally over the test surface using a transient thermal liquid crystal test technique with a computer vision data acquisition and reduction system for various combinations of clearance heights, clearance flow Reynolds numbers, and film flow rates with different coolant injection configurations. The present results reveal a strong dependency of film cooling performance on the choice of the coolant supply hole shapes and injection locations for a given tip geometry.

Commentary by Dr. Valentin Fuster
1994;():V004T09A023. doi:10.1115/94-GT-171.
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Results of heat transfer measurements on a typical turbine blade and a vane in a linear cascade have been obtained using the naphthalene sublimation technique. The tests on the vane were performed at the nominal flow angle, whereas for the turbine blade an off-design angle was chosen to study the influence of a separation bubble on the heat transfer. The exit Mach number was varied from M2=0.2 to 0.4 and the exit Reynolds number ranged from Re2= 300000 to 700000. Comparisons with numerical codes have been conducted.

The measurements were performed in a linear test facility containing five airfoils. Two tailboards and two bypass vanes allowed to achieve a good periodicity of the flow. The aerodynamic flow conditions were measured using pressure taps and Laser-Two-Focus (L2F) anemometry. About forty static pressure taps gave a precise Mach number distribution over the suction and the pressure side of the airfoil. L2F measurements were used to determine the downstream flow angles.

The heat transfer coefficient was measured using the naphthalene sublimation technique. This method is based on the heat and mass transfer analogy for incompressible flow. A 0.5 mm thin naphthalene layer was applied to the middle airfoil and exposed to the flow for about 45 minutes. The sublimation was then measured in over 500 points on the airfoil, which allowed a high resolution of the heat transfer coefficient. Due to its high resolution, the sublimation technique shows the presence of and the precise location of the laminar-to-turbulent transition point and the separation bubble.

The measurements on the vane were compared with two separate two-dimensional boundary layer programs, which were TEXSTAN (Texas University) and TEN (Sussex University). The programs incorporate the k-epsilon turbulence model with several different formulations. The laminar-turbulent transition was predicted quite well with TEN, which slightly damps out the production of turbulent kinetic energy in order to ensure a smooth transition zone. In the case of the blade, the naphthalene sublimation technique was able to predict the size and the location of the separation bubble as well as the reattachment with a very high precision.

Commentary by Dr. Valentin Fuster
1994;():V004T09A024. doi:10.1115/94-GT-172.
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Heat transfer measurements have been made in the Oxford University Cold Heat Transfer Tunnel employing the transient liquid crystal technique. Complete contours of the heat transfer coefficient have been obtained on the aerofoil surfaces of a large annular cascade of high pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach and Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 × 106).

A novel mechanism is used to isolate five preheated blades in the annulus before an unheated flow of air passes over the vanes, creating a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the colour crystal change is recorded during the run with a miniature CCD video camera. The heat transfer coefficient is obtained by solving the one dimensional heat transfer equation for all the points of interest.

This paper will describe the experimental technique and present results of heat transfer and flow visualisation.

Commentary by Dr. Valentin Fuster
1994;():V004T09A025. doi:10.1115/94-GT-173.
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The present study compares measured and computed heat transfer coefficients for high speed boundary layer nozzle flows under engine Reynolds-number conditions (U = 230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 · 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, non-symmetric, convergent-divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low Reynolds-number k-ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Commentary by Dr. Valentin Fuster
1994;():V004T09A026. doi:10.1115/94-GT-174.
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The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed which accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter which accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

Commentary by Dr. Valentin Fuster
1994;():V004T09A027. doi:10.1115/94-GT-175.
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Increasing the thermal efficiency by higher turbine inlet temperatures is one of the most important aims in the area of gas turbine development. Because of the high temperatures not only the turbine vanes and blades have to be cooled, but also the knowledge of the mechanically and thermally stressed parts in the hottest zones of the rotor are of great interest. The prediction of the temperature distribution in a gas turbine rotor containing closed, gas-filled cavities, for example in between two discs, has to account for the heat transfer conditions encountered in these cavities. In an entirely closed annulus forced convection is not present, but a strong natural convection flow exists, induced by a non uniform density distribution in the centrifugal force field.

In /3/ experimental and numerical investigations on rotating cavities with pure centripetal heat flux had been carried out. The present paper deals with investigations on a pure axially directed heat flux. An experimental set-up was designed to realize a wide range of Ra-numbers (2·108<Ra<5·1010) usually encountered in cavities of gas turbine rotors.

Parallel to the experiments numerical calculations have been conducted. The numerical results are compared with the experimental data. The numerical scheme is also used to account for the influence of Re-numbers on heat transfer without changing the Ra-number. This influence could not be pointed out by experiments, because a variation of the Re-Ra characteristic of the employed annuli was not possible.

It was found that the numerical and experimental data are in quite good agreement, with exception of high Ra-numbers, where the numerical scheme predicts higher heat transfer than the experiments show. One reason may be that in the experiments the inner and outer cylindrical walls were not really adiabatic, an assumption used in the numerical procedure. Moreover the assumption of a 2-D flow pattern may become invalid for high Ra-numbers. The influence of 3-D effects was studied with the 3-D-version of the numerical code.

In opposite to the radial directed heat transfer it was found that the Nu-number is much smaller and depends strongly on the Re-number — whereas the radial heat transfer is only weakly influenced by the Re-number.

Commentary by Dr. Valentin Fuster
1994;():V004T09A028. doi:10.1115/94-GT-178.
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The current view of film cooling/heating behavior is largely the result of room temperature experiments in which the high temperatures typical of gas turbines were only simulated. The simulation rests on the assumption/deduction that the effect of temperature on film cooling behavior is due solely to the effect of temperature on fluid density.

A few experiments reported in the literature have included wide variation in temperature. In this article, the data from several of these are examined in order to determine the actual, observed effect of temperature on film cooling behavior.

Literature data exhibit a highly linear relationship between Taw and Tfc when the film is injected through a slot, and Tfc/Tms lies in the range 0.8 to 1.27. The data also indicate that this relationship is highly nonlinear when Tfc/Tms is less than approximately 0.8. The nonlinearity is so pronounced that Taw may not decrease even though (Tfc/Tms) is decreased from 0.57 to 0.35.

Nonlinearity in the relationship between Taw and Tfc has a major impact on optimum system design whenever the thermal designer has design control over the film coolant temperature.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
1994;():V004T09A029. doi:10.1115/94-GT-179.
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Results from a new facility for measuring heat transfer in transonic turbine cascades are repotted. An air heater has been built into the blow-down wind tunnel to heat the main flow for a 20 second run time. This allows control of the direction and magnitude of the heat transfer into the blade throughout the tests. A Heat Flux Microsensor was inserted into the blade to measure simultaneous surface heat flux and temperature. Measurements were made on the suction surface of the blades toward the trailing edge. Because of the long run times (20 s), the adiabatic wall temperature could be determined directly from the measured surface temperature and heat flux. Simultaneous pressure measurements were made with a Kulite transducer at the same distance from the leading edge to document shock passage. A separate shock tube was used to generate a shock wave which was introduced into the test section in front of the cascade. This shock was carried over the blade by the main flow. The resulting changes in heat flux correlated strongly with the unsteady pressure changes. An overall increase of 1.5 W/cm2 in heat flux was recorded for a pressure increase of 7 kPa during the initial passage of the shock.

Commentary by Dr. Valentin Fuster
1994;():V004T09A030. doi:10.1115/94-GT-180.
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The coefficients of discharge of 30° inclined holes having a length to diameter ratio of 6, and rounded entries or exits have been measured for a range of crossflow conditions. The rounding radius varied from 0 to 1 hole diameters, and the crossflow Mach numbers from 0 to 0.5.

Rounding the hole inlet was found to be beneficial, with increases of up to 15% being obtained at high coolant (inlet) side crossflow Mach numbers. Rounding the exit produced no significant benefit.

The crossflow effects have been correlated using inlet and outlet additive loss coefficients. These reflect the changes in pressure drop across the hole necessary to maintain the hole mass flow rate when crossflows are applied.

The correlated data have been incorporated in a computer program which gives good predictions of discharge coefficient in the presence of either a coolant crossflow or a mainstream crossflow or both.

Commentary by Dr. Valentin Fuster
1994;():V004T09A031. doi:10.1115/94-GT-181.
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Recent work, Van Treuren et al. (1993), 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 array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000–40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is confined on three sides and spent flow is allowed to exit in one direction. Local values are averaged and compared with previously published data in related geometries. The current data for a staggered array is compared to those from an inline array with the same hole diameter and pitch for an average jet Reynolds number of 10,000 and channel height to diameter ratio of one. A comparison is made between intensity and hue techniques for measuring stagnation point and local distributions of heat transfer. The influence of the temperature of the impingement plate through which the coolant gas flows on the target plate heat transfer has been quantified.

Commentary by Dr. Valentin Fuster
1994;():V004T09A032. doi:10.1115/94-GT-182.
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In continuation of earlier studies comparing heat transfer results for flow over a backward facing step and a jet in crossflow, a comprehensive data base for slot film cooling is presented. Specifically, heat transfer measurements adjacent to the injection slot for high blowing ratios were of interest. The heat transfer distributions for these conditions are of increasing significance in modern combustor liners. The new data base includes velocity and temperature profile measurements, adiabatic wall temperature and heat transfer measurements and will serve as a data base for testing newly developed numerical models.

Commentary by Dr. Valentin Fuster
1994;():V004T09A033. doi:10.1115/94-GT-183.
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A new model is presented in this paper to calculate the pressure drop and the heat transfer coefficient for a rectangular duct with two smooth walls and two rough walls. Ribs on the rough walls may be at an angle with the main flow and are distributed in a repeated pattern. The model is based on the law-of-the-wall theory, which is known to give satisfactory results for turbulent flows in a circular duct or a channel, and for two-dimensional boundary layer flows. When the theory is applied to a rectangular duct, it gives simplified relationships between the friction, heat transfer coefficients, the flow Reynolds number, and geometry parameters, which include the rib angle, rib height, the rib pitch, and the duct aspect ratio. Comparisons with experimental data show that the present model gives satisfactory results for a wide range of Reynolds numbers and geometry parameters. A Prandtl number dependence is retained for applications involving fluids other than air.

Commentary by Dr. Valentin Fuster
1994;():V004T09A034. doi:10.1115/94-GT-185.
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This paper considers the fluid dynamic principles determining the consequences of mainstream fluid ingressing to the comparatively shallow space between the rotor disc and the ring used in many designs of axial-flow turbo-machine, especially compressors, to support the stator blades at their inner ends. Windage power due to friction between this fluid and the bounding walls of this annular space, or ‘stator well’, can lead to substantial temperature rises in this region. The feasible range of flow regimes is first developed, especially as influenced by leakage through the internal seals beneath the stators separating adjacent wells. Using published data, on windage coefficients and the effects of geometry on the flow through the wells, very little of which has been obtained from truly representative flow conditions or geometries, calculations have been made to estimate the likely rises in temperature to be anticipated in realistic well designs. Leakage rates appear, not unexpectedly, to be crucial in determining these temperature rises, but the geometries of the system are little less critical, in particular the ratio of the outer to inner radiuses of the stator well and the outer peripheral clearances between rotor and stator surfaces. Leakage into a well from its adjacent neighbour is shown to lead to higher temperature rises downstream of the labyrinth seal and the possible effects of recirculation through stator wells from the mainstream boundary layer could be significant.

Commentary by Dr. Valentin Fuster
1994;():V004T09A035. doi:10.1115/94-GT-196.
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The two-equation models (k-ε) have been employed to predict turbulent flow and heat transfer for radially outward flow in a cooling duct rotating in orthogonal mode. The low-Reynolds-number model, which permits integration of the Navier-Stokes equations to the wall, has been used. The results from the low-Re model and the high-Re model with “Wall Function” are compared with the experimental data available in literature. Computations have been made for a range of Reynolds numbers (2500 to 25000) and a range of rotation numbers (0.088 to 0.24). Different conditions such as uniform wall temperature, uniform wall heat flux and uneven wall temperatures have been used as boundary conditions for heat transfer. The low-Re model does not perform as well as the Wall Function model in predicting heat transfer for flows at high Reynolds number. However, the low-Re model predictions are better than those from the high-Re Wall Function model for flows at low Reynolds number. In fact, for the geometry considered (1.27 cm × 1.27 cm duct) it becomes necessary to use the low-Re model for flows at low Reynolds number because of the limitation of the Wall Function. Heat transfer predictions from the low-Re model are within 10–40% for flows at low Reynolds number. The disadvantage of the low-Re model, in addition to the large number of cells requirement, is the slow convergence rate.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
1994;():V004T09A036. doi:10.1115/94-GT-197.
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This paper reports the results of a numerical study on the fluid flow and heat transfer in a rotating square duct with 180 deg. bend. The computations are based the standard k-ε turbulence model with wall functions. At a fixed Reynolds number, results have been obtained over a range of Rotation numbers and coolant-to-wall temperature ratios. These results reflect the complex interaction of Coriolis forces, buoyancy forces, and curvature effects. For the outward leg, rotation causes the heat transfer enhancement on the trailing surface and degradation on the leading surface. However, in the inward leg, there is heat transfer degradation on the trailing surface and enhancement on the leading edge. The buoyancy forces cause further degradation in the heat transfer on the leading surface and enhancement on the trailing surface of the outward leg.

Commentary by Dr. Valentin Fuster
1994;():V004T09A038. doi:10.1115/94-GT-232.
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A transient heat transfer method which uses liquid crystals has been applied to a scale model of a turbine rotor blade passage. Detailed contours of local heat transfer coefficient are presented for the passage in which the heat transfer to one wall was enhanced firstly by ribs and then with ribs combined with holes. The hole geometry and experimental dimensionless flow rates were representative of those occurring at the entrance to engine film cooling holes. The results for the ribbed passage are compared to established correlations for developed flow. Qualitative surface shear stress distributions were determined with liquid crystals. The complex distributions of heat transfer coefficient are discussed in the light of the interpreted flow field.

Commentary by Dr. Valentin Fuster
1994;():V004T09A039. doi:10.1115/94-GT-244.
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This paper describes heat transfer measurements on the external surface of a Natural Laminar Flow (NLF) nacelle. The measurement technique employed temperature sensitive liquid crystals and platinum resistance thermometers (PRTs) to measure the surface temperature over an electrically heated pad. This gave an immediate visual indication of the transition location. The heat transfer distribution along the length of the pad has been determined and is compared with a simple theoretical model. Results are presented for the cruise condition of Mach 0.56 at an altitude of 6400m.

Commentary by Dr. Valentin Fuster
1994;():V004T09A040. doi:10.1115/94-GT-245.
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The present study is an experimental investigation of the effects of free-stream turbulence and surface riblets on the heat transfer rate in a linear turbine cascade. The primary goal of the study is to determine if surface riblets will reduce the average heat transfer rate in a cascade in the absence and in the presence of free-stream turbulence. A smooth, airfoil shaped, constant temperature, heat transfer test surface was inserted into a linear cascade facility where heat transfer tests were run at three levels of Reynolds number and two levels of free-stream turbulence. The heat transfer test surface was then removed from the facility so that riblets could be engraved on its surface. The newly ribleted heat transfer surface was then re-inserted into the cascade facility, where a second set of heat transfer tests were run at the same set of conditions used during the testing of the test surface while it was smooth. The test results indicate that, under certain conditions, surface riblets reduce the average heat transfer rate in the cascade by 7%.

Commentary by Dr. Valentin Fuster
1994;():V004T09A041. doi:10.1115/94-GT-275.
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Anti-icing air from the internal nose cowl regions of aircraft engines exits via an exhaust slot to join the engine intake air upstream of the compressor. It is important that this still hot air be used efficiently downstream of the exhaust slot to effect heating of the downstream surface (acoustic liner) to facilitate the prevention of ice build-up at this point. To this end, various exhaust slot geometry designs have been investigated in an experimental study to provide guidelines to assist in this aim. The most significant variables were found to be assembly length, slot depth, exit plane width and exhaust angle. Surface heating effectiveness does not appear to be affected by “blowing ratio” differences between exhaust geometries. Equations are derived and suggested to predict the skin temperature decay downstream of the exhaust slot for a range of “blowing ratios” but the benefits in anti-icing performance must be considered ultimately against weight, cost, reliability, maintenance factors and in-service experience.

Commentary by Dr. Valentin Fuster
1994;():V004T09A042. doi:10.1115/94-GT-276.
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Various nose cowl internal geometry designs have been investigated in a study relating to the effect of hot air mass flows in the prevention of ice formation on the external nose cowl (lipskin) surfaces of aero-engine intakes. Significant differences in the lipskin surface temperature levels were observed as the internal, hot, anti-icing air distribution geometry was altered. A double-skinned arrangement (in which the hot air was closely confined to the region requiring protection against ice formation) was observed to be particularly advantageous in this respect. The effectiveness of this design was matched however by a conventional “piccolo” pipe distribution system whilst the remaining two internal Builds investigated were found to be not as effective. In evaluating the benefits that accrue from a particular design, factors such as weight, cost, reliability, maintenance and in-service experience must also be considered.

Commentary by Dr. Valentin Fuster
1994;():V004T09A043. doi:10.1115/94-GT-277.
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The Isentropic Light Piston Facility (ILPF) at Pyestock has been upgraded to include a single stage, high pressure turbine. All major non-dimensional parameters are accurately scaled during the 0.4s run time, enabling heat transfer and aerodynamic measurements to be made at engine representative conditions. The ILPF was previously an annular cascade facility. This paper describes the design and integration of the rotor module and the results of the commissioning tests. An important feature is a novel, patented, turbobrake which is shown to maintain the turbine at a constant speed during the run.

Topics: Turbines , Pistons
Commentary by Dr. Valentin Fuster
1994;():V004T09A044. doi:10.1115/94-GT-290.
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A colour image processing system for liquid crystal heat transfer experiment has been developed. The system is capable of digitizing and processing the complete liquid crystal surface colour (hue) change history in a transient test and, together with a calibration, can give the complete history of surface temperature over a full surface. Two methods for automatically processing the hue history to give heat transfer coefficient distributions are presented. Both methods raise the accuracy of the transient technique above other approaches by using the redundancy inherent in the multiple surface temperature measurements. The first regression approach applied to the determination of both h and Tgas is reported. The uncertainty in all measurements has been quantified and examples of applications of both techniques given.

Commentary by Dr. Valentin Fuster
1994;():V004T09A045. doi:10.1115/94-GT-296.
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Surface heat transfer and skin friction enhancements, as a result of freestream turbulence levels between 10% < Tu < 20%, have been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulence levels, the skin friction and heat transfer enhancements scale best using parameters which are a function of turbulence level and dissipation length scale. However, as turbulence levels approach Tu = 20%, the St′ parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles, the maximum streamwise rms value in the near-wall region, which is needed for St′, is the same as that measured in the freestream at Tu = 20%. Analogous to St′, a new parameter, Cf, was found to scale the skin friction data. Independent of all the correlations evaluated, the available data show that the heat transfer enhancement is greater than enhancements of skin friction with increasing turbulence levels. At turbulence levels above Tu = 10%, the freestream turbulence starts to penetrate the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction. Although inactive motions do not contribute to the shear stress, these motions are still active in removing heat.

Commentary by Dr. Valentin Fuster
1994;():V004T09A046. doi:10.1115/94-GT-306.
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This paper evaluates the basic feasibility and anticipated benefits to using heat pipe technology to cool the turbine vanes of gas turbine engines.

This concept involves fitting out the vane interior as a heat pipe, extending the vane into an adjacent heat sink and then transferring the vane incident heat through the vane to the heat sink. The baseline is an advanced military fighter engine and the bypass air is the chosen heat sink. The results of this study show a 7.2% increase in engine thrust, a 0.2% decrease in specific fuel consumption with engine weight increased by less than 1% by using this technology.

Commentary by Dr. Valentin Fuster
1994;():V004T09A047. doi:10.1115/94-GT-307.
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Complete distributions of local heat transfer coefficient have been measured over the full surface of a pedestal bank at a number of Reynolds numbers. The transient heat transfer method with thermochromic liquid crystals used as the surface thermometer was used to obtain the data. The pedestal geometry included fillet radii representative of those used in engine blade cooling passages. The heat transfer coefficient distributions are compared to previously reported local measurements made on a bank of plain cylinders. Averaged values based on the local mixed bulk gas temperature are compared to established correlations. The distributions of local heat transfer coefficient show a remarkable periodicity when based on a local temperature. These patterns are discussed in terms of the interpreted flow field. Measurements of pressure drop are also reported and, for a range of engine representative Reynolds numbers, agree with an existing correlation for prismatic pedestals.

Commentary by Dr. Valentin Fuster
1994;():V004T09A048. doi:10.1115/94-GT-311.
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Heat transfer coefficients have been measured for film cooling injection from a single row of holes laterally directed with a compound angle of 60°. Two hole configurations were tested, round holes and holes with a diffusing expansion at the exit. Streamwise directed round holes were also tested as a basis for comparison. All the holes were inclined at 35° with respect to the surface. The density ratio was 1.0, momentum flux ratios ranged from I = 0.16 to 3.9 and mass flux ratios from M = 0.4 to 2.0. Results are presented in terms of hf/h0, the ratio of film cooling heat transfer coefficient to the heat transfer coefficient for the undisturbed turbulent boundary layer at the same location. Results indicate that for the streamwise directed holes, the heat transfer rates are close to the levels that exist without injection. Similarly, at low momentum flux ratio, holes with a large compound angle had little effect on heat transfer rates. But at high momentum flux ratios, holes with a large compound angle had significantly increased heat transfer levels. The results were combined with adiabatic effectiveness results to evaluate the overall performance of the three geometries. It is shown that for evaluation of film cooling performance with compound angle injection, especially at high momentum flux ratios, it is critical to know the heat transfer coefficient, as the adiabatic effectiveness alone does not determine the performance. Compound angle injection at high momentum flux ratios gives higher effectiveness values than streamwise directed holes, but the higher heat transfer levels result in poorer overall performance.

Commentary by Dr. Valentin Fuster
1994;():V004T09A049. doi:10.1115/94-GT-312.
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Film cooling effectiveness was studied experimentally in a flat plate test facility with zero pressure gradient using a single row of inclined holes which injected high density, cryogenically cooled air. Round holes and holes with a diffusing expanded exit were directed laterally away from the freestream direction with a compound angle of 60°. Comparisons were made with a baseline case of round holes aligned with the freestream. The effects of doubling the hole spacing to six hole diameters for each geometry were also examined. Experiments were performed at a density ratio of 1.6 with a range of blowing ratios from 0.5 to 2.5 and momentum flux ratios from 0.16 to 3.9. Lateral distributions of adiabatic effectiveness results were determined at streamwise distances from 3 D to 15 D downstream of the injection holes. All hole geometries had similar maximum spatially averaged effectiveness at a low momentum flux ratio of I = 0.25, but the round and expanded exit holes with compound angle had significantly greater effectiveness at larger momentum flux ratios. The compound angle holes with expanded exits had a much improved lateral distribution of coolant near the hole for all momentum flux ratios.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
1994;():V004T09A050. doi:10.1115/94-GT-326.
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An experimental study was undertaken to gain insight into the physical mechanisms that affect the laminar-turbulent transition process downstream of the leading-edge roughness condition. Three sizes of sandpaper strips were chosen to simulate the randomly distributed roughness located near the leading edge of a turbine blade, and three sizes of cylinders were chosen to simulate the relatively isolated peak nature of the roughness structure. The roughness Reynolds numbers tested covered a wide range, from 2 to 2840. The roughness sizes were selected based on the measured roughness characteristics of used gas turbine blades. The results indicated that at low free-stream velocities (5 m/s), the maximum roughness height was the primary contributor to deviations from the undisturbed case. At higher free-stream velocities (5–7 m/s), three of the rough leading-edge conditions exhibited a dual-slope region between the laminar and turbulent Stanton number versus Reynolds number correlations. Analysis of the boundary layer indicated that the first segment of the dual-slope was laminar, but the wall heat transfer significantly deviates from the laminar correlation. The second segment was transitional. The dual-slope behavior and the waviness of the Stanton number distribution at higher free-stream velocities observed downstream of the rough leading-edge conditions are believed to have been caused by nonlinear amplification introduced by the finite disturbances at the leading edge.

Commentary by Dr. Valentin Fuster
1994;():V004T09A051. doi:10.1115/94-GT-337.
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Earlier heat transfer studies with orthogonal rotation were conducted mostly on ducts of square cross-section. This paper reports a different cross-section, a triangular duct. Unlike a square cross-section, the triangular shape provides more restriction to the formation of the secondary flows. Moreover, the studied orientation of the right triangular duct avoids formation of symmetric vortex structures in the cross flow plane. This paper presents turbulent heat transfer characteristics of a two-pass smooth walled triangular duct. One pass is for radial outward flow and the other for radial inward flow. With rotation the radial outward and inward flow directions show different surface heat transfer characteristics. Like a square duct, differences between the trailing and the leading Nusselt number ratios for the triangular duct increase with rotation number. However, the rate of change of Nusselt number ratios with rotation number varies for the two duct geometries. Standard k-ε model predictions for a radial outward flow situation show that the Nusselt number ratio variations with Reynolds number are not drastic for the same rotation number.

Topics: Heat transfer , Ducts
Commentary by Dr. Valentin Fuster

Electric Power

1994;():V004T10A001. doi:10.1115/94-GT-238.
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The last decade has seen remarkable improvement in industrial gas turbine unit size and performances. The coming years and decades hold the promise of even more progress in these fields.

Simultaneously, the fuel utilization achieved by combined cycles has been steadily increased, which is a combination of improvements both in the gas turbine technology and in the new combined cycle schemes with multiple pressure levels.

These combined cycles quite often have to operate on a load cycling duty or in the intermediate load range, so that not only the design point performances but even the off design are sufficient to ensure the plant profitability. Its transient behaviour, its ability to start quickly and reliably, are key parameters when selecting the plant.

This paper describes a method developed for the calculation of the transient performances of combined cycles, from no load situations, including cold conditions, to full load. The method is then applied and illustrated with a recently commissioned plant, for which some transient measurements are available.

Commentary by Dr. Valentin Fuster
1994;():V004T10A002. doi:10.1115/94-GT-239.
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Heat Recovery Steam Generator start-ups are most often thought of as being a delicate step in the pressurization of the boiler, as are trips and shutdowns. One reason for this is the so-called swell effect and the problems which can arise when this event occurs while another might be the different controls that have to be monitored at the same time. A dynamic software is actually used by Cockerill Mechanical Industries (C.M.I.) to simulate the behaviour of all significant thermodynamic variables of the system as well as the temperatures of the materials, and typical control variables versus time.

During the development of this software, special care has been given to the study of the influence of the vaporizer pressure drop on the temperature and pressure gradient at the inlet of the drum, where critical thermal and mechanical stresses might appear. The circulation pump specifications have been taken into account. A discussion is presented in order to measure the influence of this pressure drop on the highest observed stresses during the swell effect as well as the pressure gradient used during the pressurization on the fatigue analysis of the drum and its nozzles. Their design is then briefly overviewed using two methods of calculations.

Commentary by Dr. Valentin Fuster
1994;():V004T10A003. doi:10.1115/94-GT-240.
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The humid air turbine (HAT) cycle, proposed by Mori et al. and recently developed by Rao et al. at Flour Daniel, has been identified as a promising way to generate electric power at high efficiency, low cost and simple system relative to combined cycle and steam injection gas turbine cycle. It has aroused considerable interest.

Thermodynamic means, such as intercooling, regeneration, heat recovery at low temperature and especially non-isothermal vaporisation by multi-phase and multi-component, are adopted in HAT cycle to reduce the external and internal exergy losses relative to the energy conversion system. In addition to the parameter analysis and the technical aspect of HAT cycle, there is also a strong need for “systems” research to identify the best ways, of configuring HAT cycle to integrate all the thermodynamic advantages more efficiently to achieve high performance.

The key units in HAT cycle are analyzed thermodynamically and modelled in this paper. The superstructure containing all potentially highly efficient flowsheeting alternatives is also proposed. The system optimization of the HAT cycle is thus represented by a nonlinear programming problem. The problem is solved automatically by a successive quadratic algorithm to select the optimal configuration and optimal design parameters for the HAT cycle.

The results have shown that the configuration of the HAT cycle currently adopted is not optimal for efficiency and/or specific power, and the current pressure ratio are too high to be favorable for highest performance. Based on the current technical practice, the optimal flowsheeting for thermal efficiency can reach 60.33% when TIT=1533K, while the optimal flowsheeting for specific power can achieve 1300kW/kg/s air for TIT at 1533K. The optimal flowsheeting configuration is compared favorably with the other existing ones.

Commentary by Dr. Valentin Fuster
1994;():V004T10A004. doi:10.1115/94-GT-278.
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This paper covers the design of heat recovery steam generators (HRSG).

The design of the HRSG plays an important role in overall design of a combined cycle unit. The primary focus of the paper is the influence of the boiler on the total efficiency of the combined cycle.

Commentary by Dr. Valentin Fuster
1994;():V004T10A005. doi:10.1115/94-GT-279.
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Data on the distribution by size of generator-drive gas turbines insured by Allendale Insurance, Arkwright and Protection Mutual insurance companies is presented. Similar data on loss costs is included. The principal failure modes are shown and described. Finally, a comprehensive table outlining the causes of these failure modes, and the optimum approaches to their prevention, is given.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A006. doi:10.1115/94-GT-303.
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Four key parameters, the 4 S’s, determine the technoeconomical performance of the steam bottoming cycle to a given gasturbine: [S1], the temperature of the heat Source, [S2], the temperature of the heat Sink, [S3] cycle Structure and [S4] component Specifications. The first two are given by the gasturbine exhaust gas temperature (TEX) and ambient water/air temperatures respectively; the last two are designer’s choice but depend on economics: how much can you afford to pay for an extra kW? (parity factor or differential capital outlay).

The paper analyses the effect of current trends in the first two S’s on the latter two: «S1», the higher TIT (turbine inlet temperature) of advanced GT’s generally leads to higher TEX, especially when coupled with Sequential Combustion; and [S2]«S2», the trend from fresh water cooling to cooling towers — and again from wet to dry types — due to environmental considerations and/or water shortages leads to higher condenser pressures. These trends change the economics of «S3», the structure (one-, two- or three-pressure, reheat, supercritical etc.); finally, macro-economical trends (fuel cost, cost of capital, more Independent Power Producers or IPP’s) determine «S4», equipment specifications (delta-T’s, delta-P’s, number of stages or exhaust flows etc.).

In this written paper the authors report on their technoeconomical analysis; at the conference they will present hands-on solutions, optimized for ABB’s Type GT24 (60Hz, 165 MW) and GT26 (50 Hz, 240 MW) gasturbines. (Note that throughout the paper definite figures are only given for ABB gasturbines and steam turbines, as the authors cannot vouch for information published by other manufacturers or third parties).

Commentary by Dr. Valentin Fuster
1994;():V004T10A007. doi:10.1115/94-GT-304.
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Computer modelling of Performance optimization was done to examine the effect of key operating variables like compressor pressure ratio, turbine inlet temperature, and recovery boiler pressure on performance parameters of a simple combined cycle and comparison was made to a simple gas turbine cycle. Both thermal efficiency and specific net work were examined as pressure ratio and recovery boiler pressure were varied for each turbine inlet temperature. Also careful consideration was given to admissible values of stack gas temperature, steam turbine outlet dryness fraction, and steam turbine outlet dryness fraction, and steam turbine inlet temperature.

Specifically, it was shown that when we treat a combined cycle as an integrated system, efficiency optimization entails a pressure ratio below that suitable for simple gas turbine plant.

Commentary by Dr. Valentin Fuster
1994;():V004T10A008. doi:10.1115/94-GT-308.
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This paper summarizes the results of the technical and economic data of nominal 280 MW Compressed Air Energy Storage Plants (CAES) using caverns in salt domes located in southeastern parts of Mississippi for intermediate duty generation of 1,000 hours per year and peaking duty generation of 750 hours per year. The plants are assumed to operate 90% time on Natural Gas and 10% of the time on No. 2 distillate. A weekly cycle of 10 hours of generation and 12 hours of charging daily with 15 hours of weekend charging was the basis for the study. The study includes conceptual layout, optimization, detailed cost analyses, reliability and operation and maintenance of the Compressed Air Energy storage plant. The objective of the study is low capital cost of the CAES plant and optimum performance.

Commentary by Dr. Valentin Fuster
1994;():V004T10A009. doi:10.1115/94-GT-310.
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The paper will discuss the application of Thermal Energy Storage (TES) using ice and inlet air cooling at the Fayetteville (North Carolina, USA) Public Works Commission (PWC) Butler-Warner Generation Plant. The Butler-Warner Generating Plant consists of eight General Electric Frame 5 combustion turbines and a single steam turbine. Six of the combustion turbines exhaust through three Heat Recovery Steam Generators (HRSG). The project consisted of modifying the inlets of all eight combustion turbines to accommodate plate fin cooling coils and new air filters; and the design and construction of the TES ice production and storage facilities. A feasibility study was completed in June 1992. Detail designed began in August 1992. Initial operation was June 1993. The modifications have been completed and the plant has experienced a 29% capacity increase as a result of the project.

Commentary by Dr. Valentin Fuster
1994;():V004T10A010. doi:10.1115/94-GT-329.
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The use of naphtha as gas turbine fuel has been limited. In advanced countries naphtha is usually cracked to produce gasoline, or ethylene which commands premium rates in the market. In developing countries like India, however, the scenerio is much different. The market for the cracked products is not abundant. In addition, the paucity of natural gas has rather forced the authorities of power plants to use naphtha as alternative gas turbine fuel.

Commentary by Dr. Valentin Fuster
1994;():V004T10A011. doi:10.1115/94-GT-331.
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Heavy, brittle and very hard deposits built on the first row vanes have caused severe erosion of all the first stage blades of a gas turbine during operation with washed and treated heavy residual fuel oil. The high sulphur (3.5–4.0 wt.%) fuel oil consumed by the turbine is also high in vanadium (280–290 ppm) and asphaltene content.

In the present work the results of an investigation on the physical and chemical characteristics of erosive ash deposits as a function of operation conditions and fuel oil characteristics are presented. The structure and chemistry of deposits were studied by chemical analysis, x-ray diffraction, microanalysis and scanning electron microscopy. It was confirmed that deposit friability is enhanced by its MgSO4 content and that its hardness depends on the amount of MgO present. It was also found a clear correlation between the gas inlet temperature and the size of the ash particles deposited, and on the degree of compactness and hardness of the deposit. The role of the unburned particles, unavoidable in the combustion of heavy fuel oils, is discussed in relation to their influence on the effectiveness of the magnesium inhibitor.

Commentary by Dr. Valentin Fuster
1994;():V004T10A012. doi:10.1115/94-GT-351.
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Often, turbine and generator rotors are produced from a single forging or from two forged bearing ends with a stack of discs in between. As with many other components in rotary equipment these precision machined forgings can be damaged or worm during operation. Due to the sensitivity of the material to any kind of heat treatment, including welding, repair of this damage presents a challenge for repair engineers.

This paper will give a general overview of repair. Repair may include welding, heat treatment, plasma spraying, shaft straightening, stress relieving, etc. Some recent repairs will be discussed.

Topics: Maintenance , Rotors
Commentary by Dr. Valentin Fuster
1994;():V004T10A013. doi:10.1115/94-GT-388.
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In cooperation with U.S. Department of Energy’s Morgantown Energy Technology Center, a Westinghouse led team is working on the second part of an 8-year, Advanced Turbine Systems Program to develop the technology required to provide a significant increase in natural gas-fired combined cycle power generation plant efficiency.

This paper reports on the Westinghouse program to develop an innovative natural gas-fired advanced turbine cycle which, in combination with increased thing temperature, use of advanced materials, increased component efficiencies and reduced cooling air usage, has the potential of achieving a lower heating value plant efficiency in excess of 60%.

Commentary by Dr. Valentin Fuster
1994;():V004T10A014. doi:10.1115/94-GT-411.
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The U.S. Department of Energy (DOE) is sponsoring a program to conduct design and development, leading to full scale demonstration of advanced gas turbine systems. The Advanced Turbine Systems (ATS) program is jointly administered by the DOE Office of Fossil Energy (DOE/FE) and the Office of Energy Efficiency and Renewable Energy (DOE/EE). The program will demonstrate commercial prototypes of both utility- and industrial-scale ATS by the year 2000.

The ATS program objectives are: system efficiency 60 percent (lower heating value [LHV]) or greater for utility-scale systems, and an equivalent 15 percent improvement for industrial systems; environmental superiority without the use of post combustion emissions controls; busbar energy costs 10 percent lower than current systems; adaptability to coal or biomass firing; and reliability, availability and maintainability equivalent to current advanced turbine systems.

A competitive procurement process is being used for the selection of contractors to develop and demonstrate full scale systems. System studies were completed by six U.S. turbine manufacturers, and awards were announced in August 1993 for “concept development.” This paper describes one implementation approach to achieve the DOE/ATS targets.

Topics: Turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A015. doi:10.1115/94-GT-412.
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Tohoku Electric Power Co., Inc. and Mitsubishi Heavy Industries, Ltd. have begun a joint development program on key technologies for a next generation gas turbine which aims for a combined cycle efficiency over 55%. Under the program, advanced cooling technologies, better heat resistant materials and thy low NOx (DLN) combustion technologies are being developed. For verifying high temperature technologies, turbine testing is going to be performed using the HTDU (High Temperature Demonstration Unit) at Takasago Machinery Works, Mitsubishi Heavy Industries, Ltd.

This paper describes the general description of the HTDU facility and plans for testing a turbine at a firing temperature of 1500°C.

Commentary by Dr. Valentin Fuster
1994;():V004T10A016. doi:10.1115/94-GT-421.
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Long before the neologism “Cogeneration” was coined (around 1978), UEM’s Chambière Power Plant — which dates back to the turn of the century — was already supplying the city of Metz, east of France, with combined heat and power.

In 1992, Chambière experienced a major turning point in its history with the installation of a new unit based on one MS 6001B “Heavy Duty” gas turbine. This model, rated 38 MWe - ISO and burning natural gas or fuel oil has become the core of a new cogeneration unit exhibiting an outstanding performance:

- efficiency higher than 80% (LHV) providing a 20% energy saving in comparison to a conventional plant,

- low pollutant emissions (NOx, CO, HC) and low contribution to the greenhouse-effect (CO2).

The gas turbine has been equipped with two steam injection devices, for DeNOx and power augmentation respectively, resulting in a very flexible system.

After describing the power plant and giving its main achievements in the fields of energy and emissions, the paper briefly presents several improvements intended to protect both the turbine and the environment.

Commentary by Dr. Valentin Fuster
1994;():V004T10A017. doi:10.1115/94-GT-423.
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This paper discusses the thermodynamics of power cycles where steam or water are mixed with air (or combustion gases) to improve the performance of stationary gas turbine cycles fired on clean fuels. In particular, we consider cycles based on modified versions of modern, high-performance, high-efficiency aero-derivative engines.

The paper is divided into two parts. After a brief description of the calculation method, in Part A we review the implications of intercooling and analyze cycles with steam injection (STIG and ISTIG). In Part B we examine cycles with water injection (RWI and HAT).

Due to lower coolant temperatures, intercooling enables to reduce turbine cooling flows and/or to increase the turbine inlet temperature. Results show that this can provide significant power and efficiency improvements for both simple cycle and combined cycle systems based on aero-engines; systems based on heavy-duty machines also experience power output augmentation, but almost no efficiency improvement.

Mainly due to the irreversibilities of steam/air mixing, intercooled steam injected cycles cannot achieve efficiencies beyond the 52–53% range even at turbine inlet temperatures of 1500°C. On the other hand, by accomplishing more reversible water-air mixing, the cycles analyzed in Part B can reach efficiencies comparable (RWI cycles) or even superior (HAT cycles) to those of conventional “unmixed” combined cycles.

Topics: Cycles , Steam
Commentary by Dr. Valentin Fuster
1994;():V004T10A018. doi:10.1115/94-GT-424.
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Part B of this paper focuses on intercooled recuperated cycles where water is injected to improve both efficiency and power output. This concept is investigated for two basic cycle configurations: a Recuperated Water Injected (RWI) cycle, where water is simply injected downstream the HP compressor, and a Humid Air Turbine (HAT) cycle, where air/water mixing is accomplished in a counter-current heat/mass transfer column called “saturator”.

For both configurations we discuss the selection and the optimization of the main cycle parameters, and track the variations of efficiency and specific work with overall gas turbine pressure ratio and turbine inlet temperature (TIT). TIT can vary to take advantage of lower gas turbine coolant temperatures, but only within the capabilities of current technology. For HAT cycles we also address the modelization of the saturator and the sensitivity to the most crucial characteristics of novel components (temperature differences and pressure drops in heat/mass transfer equipment). The efficiency penalties associated to each process are evaluated by a second-law analysis which also includes the cycles considered in Part A.

For any given TIT in the range considered (1250 to 1500°C), the more reversible air/water mixing mechanism realized in the saturator allows HAT cycles to achieve efficiencies about 2 percentage points higher than those of RWI cycles: at the TIT of 1500°C made possible by intercooling, state-of-the-art aero-engines embodying the above cycle modifications can reach net electrical efficiencies of about 57% and 55%, respectively. This compares to efficiencies slightly below 56% achievable by combined cycles based upon large-scale heavy duty machines with TIT = 1280°C.

Topics: Cycles , Steam , Water
Commentary by Dr. Valentin Fuster
1994;():V004T10A019. doi:10.1115/94-GT-434.
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The Medway Project is a 660 MW combined cycle power plant which employs two of the world’s largest advanced technology MS9001FA combustion turbine generators and an advanced design reheat steam turbine generator in a power plant system designed for high reliability and efficiency. This paper discusses the power plant system optimization and design, including thermodynamic cycle selection, equipment arrangement, and system operation. The design of the MS9031FA combustion turbine generator and the steam turbine generator, including tailoring for the specific application conditions, is discussed.

Commentary by Dr. Valentin Fuster
1994;():V004T10A020. doi:10.1115/94-GT-435.
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A wide variety of gas turbine based cycles exist in the market today with several technologies being promoted by individual Original Equipment Manufacturers. This paper is focused on providing users with a conceptual framework within which to view these cycles and choose suitable options for their needs. A basic parametric analysis is provided to show the interdependency of Turbine Inlet Temperature (TIT) and Pressure Ratio on cycle efficiency and specific work.

Commentary by Dr. Valentin Fuster
1994;():V004T10A021. doi:10.1115/94-GT-436.
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This paper reports about the results of a field test conducted over a period of 8000 operating hours on the effect of combined on line and off line compressor washing on a 66 MW gas turbine operating in a combined cycle plant at UNA’s Lage Weide 5 power plant in Utrecht. Observations have shown a sustained high output level close to the nominal guaranteed rating, despite difficult atmospheric conditions. Investigations on the correlations between fouling gradients in the compressor and atmospheric conditions are also presented. The evaluation of the results demonstrate the importance of implementing an optimised regime of on line and off line washing in the preventive turbine maintenance program. It will improve the plant profitability by reducing the costs of energy production.

Commentary by Dr. Valentin Fuster
1994;():V004T10A022. doi:10.1115/94-GT-437.
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A performance analysis was fulfilled to compare the steam recompression with the conventional single- and dual-pressure bottoming cycles. The optimal parameters for each cycle were found in order to maximize the exergetic efficiency. Heat transfer surface was also calculated to show the differences in the size of the heat recovery steam generator which have a direct influence on the plant’s costs.

The optimal configurations for each cycle were also studied when steam injection is employed. The relative performance when steam extraction is varied between 0 and 20% of the gas turbine’s compressor inlet mass flow rate, was also examined.

Commentary by Dr. Valentin Fuster
1994;():V004T10A023. doi:10.1115/94-GT-446.
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Through an alliance established in 1992 between Westinghouse Electric Corporation and Rolls-Royce plc, a program has been implemented that will bring the industrial Trent aero engine to the power generation marketplace. The Rolls-Royce Trent has been initially sized at 50 MW, with a development potential to higher power ratings, and is offered by Westinghouse as a complete power generation package, the “Trent EconoPac”.

The Trent EconoPac sets a new performance standard in the industry with a nominal simple cycle efficiency of 42 percent. It is also ideal for combined cycle and cogeneration applications; a net combined cycle power of 63 MW at 52 percent efficiency can be developed. This paper describes the Trent industrial engine and EconoPac and reviews the development program with emphasis on unique features that benefit the power plant operator.

Commentary by Dr. Valentin Fuster
1994;():V004T10A024. doi:10.1115/94-GT-464.
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A method of calculation of cooled gas turbine parameters is proposed. The method is based on the solution of the expansion process equation, heat transfer equations for cooled elements and on the results of the statistic processing of the parameters.

The method is valid for the turbine with any cooling system and gaseous heat carrier. Turbine output determination error does not exceed 0,5–1,0%.

The method allows to obtain the characteristics of gas turbines and gas turbine units (GTU) with open and closed air and steam cooling systems and to carry out an efficiency analysis of their performance in power generating units of various structure.

Topics: Cooling , Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A025. doi:10.1115/94-GT-471.
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The thermodynamic analysis of integrated gas/steam cycle has been carried out on the basis of second law of thermodynamics. The exergy analysis provides a viable understanding of the influence of various parameters on the distribution of losses in the constituent components of the cycle. The paper also provides the insight into the influence of changing operating parameters on the performance of the waste heat recovery boiler, which in turn questions the viability of the integrated gas/steam cycle.

Commentary by Dr. Valentin Fuster
1994;():V004T10A026. doi:10.1115/94-GT-472.
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This paper examines the vibration characteristics of large frame land-based combustion turbines including response of the entire rotor train. The typical rotor train consists of the combustion turbine with integral axial compressor, a rigidly coupled generator, and a starting and auxiliary turning gear package connected through a flexible coupling.

Vibration characteristics during both transient and steady state conditions are considered. Analytical methods for predicting synchronous and asynchronous vibration response are examined. Actual shop and field test results am discussed including vibration components at frequencies other than running speed.

Industry standards on vibration limits are discussed with respect to current Westinghouse vibration control setting specifications.

Commentary by Dr. Valentin Fuster
1994;():V004T10A027. doi:10.1115/94-GT-474.
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This paper introduces the engineering approach taken in developing the 501FA gas turbine, which is an uprated version of the existing 501F 150MW class gas turbine. The concepts and procedures which were utilized to uprate this gas turbine are also presented. To achieve better performance, new techniques were incorporated which reflected test results and operating experience. No advanced technologies were introduced. Instead, well experienced techniques are adopted so as not to deteriorate reliability. Improvement of the performance was mainly achieved mainly due to the reduction of cooling air. Tip clearances were also optimized based on shop test and field results.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A028. doi:10.1115/94-GT-488.
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This paper reviews the evolution of heavy-duty power generation and industrial combustion turbines in the United States from a Westinghouse Electric Corporation perspective. Westinghouse combustion turbine genealogy began in March of 1943 when the first wholly American designed and manufactured jet engine went on test in Philadelphia, and continues today in Orlando, Florida with the 160 MW, 501F Advanced Combustion Turbine. In this paper, advances in thermodynamics, materials, cooling, and unit size will be described. Many basic design features such as two-bearing rotor, cold-end drive, can-annular internal combustors, CURVIC2 clutched turbine discs, and tangential exhaust struts have endured successfully for over 40 years. Progress in turbine technology includes the clean coal technology and advanced turbine systems initiatives of the U.S. Department of Energy.

Commentary by Dr. Valentin Fuster
1994;():V004T10A029. doi:10.1115/94-GT-491.
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The eight General Electric MS7001B gas turbines in combined cycle service at the T.H. Wharton Station of Houston Lighting and Power currently have 85000 hours of operation with 2000 starts. The units are ready for their second major overhaul. A number of hot gas path components will require replacement at that time. Rather than replacing components one by one the user devised a Program for Reliability, Improved Maintenance and Efficiency (GT Prime) with an objective of achieving twenty additional years of trouble free service. Fortunately, the supplier had developed many improved parts for his newer units which could be applied to older machines with an attendant increase in component life, inspection intervals, system reliability, availability and performance. The significant impact on customer operating costs resulted in a very attractive payback period.

A contract for modification of all eight units was signed in December, 1991. Teardown of the first unit for modification started in November, 1992 with the rebuild and test completed in July, 1993.

This paper will discuss turbine condition, differences between the old and new parts, improved performance and reduced emissions attained as a result of implementing the program.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A030. doi:10.1115/94-GT-492.
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In response to the recent rapid increase in power demand, Chubu Electric Power is now constructing two 1,650-megawatt power plants, each consisting of seven single-shaft combined-cycle units. These will be plant Nos. 3 and 4 of the Kawagoe Power Station.

As one unit of plants, these power plants not only will be among the most powerful (in output) in the world, but will also offer the following features:

1) The main equipment of these plants, a gas turbine, will be a GE-Hitachi Model F7FA, the state-of-the-art 60 Hz model, for large equipment capacity and high efficiency. The heat recovery steam generator of each plant will use serrated fin tubes for high efficiency and compactness.

2) Plant efficiency will be at least 48.5% by means of optimizing the combined-cycle system and using the single-shaft triple-pressure reheat cycle.

3) As middle-load thermal plants, these plants are designed to use the advantages of a single-shaft combined cycle, thus offering operational convenience.

4) For global environmental preservation, which is nowadays an important concern of the local community, these plants are designed to reduce NOx emissions, warm discharge water, and noise.

5) To save labor for operation, and to improve its man-machine interface, these plant will utilize a large screen and CRT operation.

Selection of these units and systems has entailed various feasibility studies and simulations for optimization, as well as new developments and reliability verifications.

This paper takes the example of plant No. 3 to describe how the method of system selection and to present the design outline.

Commentary by Dr. Valentin Fuster
1994;():V004T10A031. doi:10.1115/94-GT-493.
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A new matching procedure adapted for multishaft gas turbines modelled with the mean line prediction method, is presented. Mass flow and pressure convergence is achieved with stage by stage marching in the flow direction where the high pressure and low pressure units are treated together. Independent iteration on the power balance gives a stable procedure that can be applied in static as well as dynamic simulations. The procedure can be accelerated with an algoritm combining an advanced version of the Ellipse equation with the mean line prediction method.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T10A032. doi:10.1115/94-GT-494.
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Near the city of Dubai a gas turbine and desalination station is presently being commissioned and has already partly been taken over by the client.

This project has been carried out within 34 months from the award of the order to the acceptance by the client by an international consortium.

Upon its completion the plant will produce 60 million gallons of drinking water per day and will have an electric capacity of 457 MW.

The paper presents the technical concept of steam generators of relatively big capacity and very low steam pressures for the production of saturated steam for two designs, i.e. an oil and gas fired self-supporting steam generator and a waste heat recovery boiler behind a gas turbine including a very powerful supplementary firing system.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster

Industrial and Cogeneration

1994;():V004T11A001. doi:10.1115/94-GT-010.
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In the late 1970’s, due to increasing electric energy costs and the potential for power interruption at Solar Turbines Incorporated’s Harbor Drive manufacturing facility, management evaluated several self-generating options available at the time. With large fluctuating loads and a very limited need for thermal energy, the appropriate solution was determined to be peak shaving.

In 1980, a 2.5-MW dual fuel industrial gas turbine generator set was installed. Its intended operating cycle was during on-peak billing periods, 5 days a week throughout the year. Through August 31, 1993, the system has accumulated 22,743 hours of use and 3879 starts. Its overall start reliability has been 99.9% with an availability of 98.2%. Payback on the installation was in 4.2 years. It has continued to generate savings since installation, with net savings for 1992 alone exceeding $470,000.

This paper highlights the key aspects of the economic methodology justifying installation of the peak shaving system, operating procedures, maintenance practices and system modifications put in place over the life of the installation.

Commentary by Dr. Valentin Fuster
1994;():V004T11A002. doi:10.1115/94-GT-017.
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The idea of re-injecting into a gas turbine cycle the steam generated by the heat recovery steam generator (HRSG) is a well-established practice, especially in small-medium size cogeneration plants operating under variable heat demand. Power augmentation, electrical efficiency increase, NOx reduction and operating flexibility are the most obvious advantages brought about by steam injection. On the other hand, the discharge to the ambient of the injected steam has two major drawbacks: (i) a relevant water consumption and (ii) the large thermal loss related to the latent heat of steam. The addition of a recuperator downstream of the HRSG, whereby steam condensation takes place, can solve both problems, by achieving very high first-law efficiencies (over 100%, if reference is made to the lower heating value) and the integral recovery of water. The present paper describes the design philosophy and the operational experience of a cogeneration plant where such a condensation is accomplished. To the Authors’s knowledge, it is the first time in the world that this is achieved with gas turbine exhausts. The plant is located inside the “CARROZZERIA BERTONE”, a car manufacturing factory near Turin, Italy. It was designed to fulfill all the energy needs of the factory: it supplies all the electricity, steam and hot water required by the industrial process and during peaking hours, sells excess electricity to the national grid, at special increased tariffs offered to energy-saving plants in Italy. The plant erection (including the recuperator/condenser) was completed in December 1992; commercial operation began in February 1993.

Commentary by Dr. Valentin Fuster
1994;():V004T11A003. doi:10.1115/94-GT-059.
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The effect of installing steam injected gas turbines in a cogeneration plant is analyzed in the aspects of unit sizing and operational planning. An optimization method is used to determine the capacities of gas turbines and other auxiliary machinery in consideration of their operational strategies for variations of electricity and thermal energy demands. Through a numerical study on a plant for district hearing and cooling, it is clarified how the installation of steam injected gas turbines in place of simple cycle ones can improve the economic and energy saving properties. The influence of capital cost of steam injected gas turbines on the unit sizing and the above properties is also clarified.

Commentary by Dr. Valentin Fuster
1994;():V004T11A004. doi:10.1115/94-GT-065.
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This paper describes the design of an uprated turbine for the GT8 gas turbine. The new turbine is installed in the GT8C gas turbine unit. The entire aero-thermal performance of the old turbine has been re-assessed and the new design improves upon the old unit by a 3.5% point increase in gas turbine efficiency. Additionally, the heat transfer and cooling of the turbine has been improved with the blading having more uniform thermal loading resulting in improved thermo-mechanical life-time. This has been achieved with better cooling technology whilst still maintaining the same cooling air mass flow. The paper describes the steps involved in the uprating.

Commentary by Dr. Valentin Fuster
1994;():V004T11A005. doi:10.1115/94-GT-066.
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The M7A-01 gas turbine is a newly developed 6 MW class single-shaft machine. With its high simple-cycle efficiency and high exhaust gas temperature. it is particularly suited for use in electric power generation and co-generation applications.

An advanced high efficiency axial-flow compressor, six can-type combustors, and a high inlet temperature turbine has been adopted. This results in a high thermal efficiency of 31.5% at the gas turbine output shaft and a high overall thermal efficiency of co-generation system.

In addition, low NOx emissions from the combustors and a long service life permit long-term continuous operation under various environmental limitations.

The results of the full load shop test, accelerated cyclic endurance test and extra severity tests verified that the performance, the mechanical characteristics and the emission have satisfied the initial design goals.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1994;():V004T11A006. doi:10.1115/94-GT-121.
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A 70-MW combined-cycle power plant was constructed in January 1989 at a manufacturing plant located in York, Pennsylvania. The purpose of the power plant was to provide the manufacturing plant with a reliable source of lower-cost process steam and electricity and to produce excess electricity for sale to the local utility company. This paper is an overview of the planning and implementation of the operation and maintenance (O&M) practices which have resulted in superior cash flow from plant operations. A primary element of the power plant project was to include the O&M needs in plant design, construction, commissioning, and start-up.

Commentary by Dr. Valentin Fuster
1994;():V004T11A007. doi:10.1115/94-GT-345.
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This paper is a presentation of systematic study on externally fired gas turbine cogeneration fueled by biomass. The gas turbine is coupled in series with a biomass combustion furnace in which the gas turbine exhaust is used to support combustion. Three cogeneration systems have been simulated. They are systems without a gas turbine, with a non top-fired gas turbine, and a top-fired gas turbine. For all systems, three types of combustion equipment have been selected: circulating fluidized bed (CFB) boiler, grate fired steam boiler and grate fired hot water boiler. The sizes of biomass furnaces have been chosen 20 MW and 100 MW fuel inputs. The total efficiencies based on electricity plus process heat, electrical efficiencies, and the power-to-heat ratios for various alternatives have been calculated. For each of the cogeneration systems, part load performance with varying biomass fuel input is presented. Systems with CFB boilers have a higher total efficiency and electrical efficiency than other systems when a top-fired gas turbine is added. However, the systems with grate fired steam boilers allow higher combustion temperature in the furnace than CFB boilers do. Therefore, a top combustor may not be needed when high temperature is already available. Only one low grade fuel system is then needed and the gas turbine can operate with very clean working medium.

Commentary by Dr. Valentin Fuster
1994;():V004T11A008. doi:10.1115/94-GT-370.
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A thorough understanding of boiler performance during start-up is essential in the design and operation of Heat Recovery Steam Generators (HRSGs). It is during this time interval that the boiler may be subjected to maximum thermal and pressure gradients. Repeated exposure to corresponding stresses may lead to the fatigue failure of the material. Despite its importance, not enough work has been done on this topic. The main objective of this research is to analyze the performance characteristics of HRSG during start-up with the help of a mathematical model. The main characteristics of interest are the steam flow, steam pressure, steam temperature and water level in the drum. The behavior of these parameters is studied during start-up at the normal operating conditions at different positions of the diverter damper, the vents and the drains. Since the superheater and evaporator sections are exposed to maximum gas temperatures, only these two sections are considered in the analysis although the given methodology could be applied to include other sections as well. Finally, a practical application of the proposed model is discussed with the help of a numerical example.

Commentary by Dr. Valentin Fuster
1994;():V004T11A009. doi:10.1115/94-GT-425.
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Of all the external factors affecting a gas turbine, inlet pressure and temperature have the greatest impact on performance. The effect of inlet temperature variations is especially pronounced in the new generation of high-efficiency gas turbines typified by the 40 MW GE LM6000. A reduction of 50 F (28 C) in inlet temperature can result in a 30% increase in power and a 4.5% improvement in heat rate. An elevation increase to 5000 feet (1524 meters) above sea level decreases turbine output 17%; conversely supercharging can increase output more than 20%.

This paper addresses various means of heating, cooling and supercharging LM6000 inlet air. An economic model is developed and sample cases are cited to illustrate the optimization of gas turbine inlet systems, taking into account site conditions, incremental equipment cost and subsequent performance enhancement.

Commentary by Dr. Valentin Fuster
1994;():V004T11A010. doi:10.1115/94-GT-447.
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Black liquor, a residual of the chemical pulp industry, is a biofuel with great potential for increasing power generation. This may be accomplished by replacing the conventional recovery process using a Tomlinson recovery boiler with black liquor gasification. In addition, there are other considerable advantages.

The gasification of black liquor gives new degrees of freedom since the combustible gas may be used in a multitude of ways. For a full scale plant, a combined cycle may be an efficient way to produce process heat and power. Comparison is made with conventional CHP using a Tomlinson boiler and a steam cycle. It is shown that the generated power could be up to twice that of the conventional plant with an electrical efficiency of 30% and a total efficiency of 77% (HHV). However, the characteristics of a combined cycle in this kind of process integrated application will be quite different than those of a stand-alone powerplant. This is clearly shown when competed with conventional natural gas fired combined cycles.

This paper includes thorough analysis of some of the most important parameters of the combined cycle. It is shown that the gas turbine characteristics are the critical factors for providing a high electric efficiency. The effects of supplementary firing we also investigated. Hereby, an optimum for the steam cycle data is established.

Commentary by Dr. Valentin Fuster
1994;():V004T11A011. doi:10.1115/94-GT-473.
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Combined heat and power plants are used to supply the heat and power needed for processes. In most cases these processes require an uninterrupted heat and power supply. For the design of such plant, considerations have to be made as to how the heat and power supply can be maintained if one of the main components, the gas turbine, the HRSG or the steam turbine is not available or trips. The paper will give solutions to increase the availability of the steam supply to the process as applied in a number of projected and executed plant designs.

Commentary by Dr. Valentin Fuster

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