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IN THIS VOLUME


Fluids Engineering

2002;():3-16. doi:10.1115/IMECE2002-33156.

Over the past few years, we have developed and applied a wide range of laser-diagnostic techniques to an equally wide range of complex flowfields at Wright-Patterson AFB. Our guiding principle in these efforts has been to employ laser-based tools to further our understanding of turbulent flames, so that in the end we improve combustor performance (e.g., thrust, emissions, etc.). We have primarily focused on three areas for development (though our areas of application have been much broader): 1) combined planar laser-induced fluorescence and particle-image velocimetry, 2) planar Doppler velocimetry, and 3) filtered Rayleigh scattering. Each of these is a powerful imaging diagnostic technique that allows the study of complex turbulent flowfields. We discuss these tools in the context of their application to turbulent flows as well as future diagnostic development.

Commentary by Dr. Valentin Fuster
2002;():17-22. doi:10.1115/IMECE2002-33164.

This paper reports non-intrusive temperature and velocity imaging measurements in gas-phase flows using acetone planar laser-induced fluorescence (PLIF) thermometry and particle image velocimetry (PIV). The details of the combined PLIF/PIV instrument and the demonstration flow facilities are provided and results are presented from a turbulent Rayleigh-Bénard convection flow (PLIF only) and from an unsteady laminar impinging jet flow (combined PLIF/PIV). The data show that PLIF temperature imaging at laboratory scales is most effective for characteristic temperature differences on the order of 100 K of more. Simultaneous gas-phase temperature-velocity images are presented which show that PLIF-PIV holds promise for detailed laboratory scale measurements for gas-phase convective heat-transfer applications at high temperature differences.

Topics: Temperature , Imaging
Commentary by Dr. Valentin Fuster
2002;():23-32. doi:10.1115/IMECE2002-33170.

This paper represents a continuation of our effort to develop a velocity evaluation scheme optimized to resolve multiphase flows. An improved adaptive hybrid scheme that integrates the dynamically adaptive cross-correlation method with a particle tracking velocimetry algorithm is developed, presented and evaluated in this paper. A detailed description of the methodology, error analysis using Monte-Carlo simulations and elaborate comparisons with established schemes and robust commercial packages are presented. Improvements were guided towards increased accuracy for resolving vortical and poly-dispersed multi-phase flows. We introduce a novel iterative scheme that localizes the cross-correlation. We incorporate state of the art elaborate image processing techniques that allow increased particle densities. A new particle pairing method based on an adaptive cross-correlation masking is introduced. Finally, a refined gaussian estimation scheme that involves only four non-saturated pixels for the particle centroid detection is proposed. Overall, the dynamically adaptive hybrid velocity evaluation scheme presented here allows superior resolution of high velocity gradients, minimizes the loss of the rotational motion of the particles, and eliminates the spatial averaging effects inherent from the cross-correlation.

Commentary by Dr. Valentin Fuster
2002;():33-42. doi:10.1115/IMECE2002-33171.

Holographic PIV (HPIV) is currently the most promising technique for truly instantaneous, three-dimensional (3D), three-component (3C) velocity field measurements for complex flows including turbulent and multiphase flows. This paper reports new understanding on some fundamental issues and challenges in HPIV including the complex 3D imaging characteristics, the extraction of full particle information (intensities, sizes, and locations) in 3D space, the extraction of particle displacements, and the huge data volume to process. The latest off-axis HPIV system will be presented, which incorporates the new understanding of imaging characteristics of particle holography, careful development of data processing algorithms, and a well-designed distributed parallel processing system. We will demonstrate capabilities of HPIV by a semi-time-series measurement of instantaneous 3D, 3C velocity fields in highly 3D vortical flow.

Commentary by Dr. Valentin Fuster
2002;():43-49. doi:10.1115/IMECE2002-33173.

We have developed a simple digital holographic PIV system for 3D measurement of turbulent and multiphase flow. This system records in-line holograms of tracer particles directly on a digital camera and reconstructs the 3D particle field numerically. Using a novel complex amplitude-based method, we are able to overcome the depth of focus problem and the speckle noise problem associated with the low resolution of digital sensors and the in-line holographic setup. In this paper we will give detailed description of our system, and present the preliminary result of the benchmark experiment using a water jet.

Commentary by Dr. Valentin Fuster
2002;():51-59. doi:10.1115/IMECE2002-33174.

This paper describes a first effort to investigate the feasibility of droplet size and shape characterization by direct laser sheet imaging using time resolved Digital Particle Image Velocimetry. A 60-degree conical, high-pressure spray generated a poly-dispersed droplet distribution. Measurements were preformed for seven planes parallel to the spray axis, and separated by 4mm. A CMOS camera recorded the DPIV images at sampling rate of 10 KHz. Advanced image processing techniques were employed to identify the droplets and individually resolve their velocity using a hybrid cross-correlation particle-tracking algorithm. Subsequently, the size distribution of each droplet was quantified using geometric optics theory to convert the droplet image information to the true droplet size. Finally, the entire volume of the spray velocity and size distributions was reconstructed in a time-averaged sense. The droplet sizes from our direct imaging DPIV system were validated using a Phase Doppler Particle Analyzer (PDPA). The calculated sizes from the direct imaging methodology were found to agree with the measured PDPA results for droplets images larger than the diffraction limited diameter. Resolution limitations introduced inaccuracy for smaller droplets. In addition, the shedding frequency of the spray ligament was observed to be on the order of 1KHz, demonstrating the feasibility of using a high speed, direct imaging system in the characterization of unsteady, liquid sheet breakup properties. This preliminary effort illustrates the potential of performing global time resolved velocity and size measurements using a simple DPIV configuration based on CMOS imaging technology.

Commentary by Dr. Valentin Fuster
2002;():61-70. doi:10.1115/IMECE2002-33175.

The objective of this study is to investigate the flow behavior within a triple-blade lawnmower deck. The test section was constructed for velocity measurement with an open bottom and side-discharge. Velocity measurements were collected at several different tangential and axial sections inside the deck. The flow behaviors are observed using Laser Doppler Velocimetry (LDV) and a high-speed video camera capturing 2000 frames per second. Several different visualization techniques have been attempted: particle feeding, water vapor injection, tuft method, and others. To further enhance the experimental accuracy, fresh sod was fed into the system simulating normal cutting conditions. Along with the extensive velocity analysis, strain and static pressure were also examined at various surface locations along the blade using linear strain gages, piezoresistive pressure transducers, and Finite Element Analysis (FEA) methods. Validation of the above analyses was performed using Computational Fluid Dynamics (CFD) investigation. It has been observed that the deck and blade configurations share equal significance in the resultant flow profiles.

Commentary by Dr. Valentin Fuster
2002;():73-80. doi:10.1115/IMECE2002-33798.

Numerical simulation of sediment transport is considered as a coupled problem based on computation of profiles of water velocity and suspended sediment concentration. Effects of the water velocity profile and turbulent pulsation on vertical motion of particles are emphasized. These effects allow explanation of amplified sediment deposit in viscous separation zones near both natural and manmade bottom irregularities (like walls of shipping channels). The unique numerical technique for separated flow computation is developed on the basis of viscous-inviscid interaction concept. This technique is validated by experimental data for turbulent flows over backward-facing steps. New results for conditions inherent to flow separation over seabed are obtained. A semi-empirical approach to determination of sediment concentration is suggested.

Commentary by Dr. Valentin Fuster
2002;():81-94. doi:10.1115/IMECE2002-33808.

The purpose of the present communication is to summarize the state-of-the art knowledge of the existing relationships between Eulerian and Lagrangian statistics in the literature. It will focus on integral scales, especially the classical Eulerian scales (such as those classically obtained from a fixed hot-wire or LDA control volume), the interesting moving Eulerian time scale (that obtained by a sensor which would move with the mean velocity) and the Lagrangian integral scale, most important for Lagrangian turbulent diffusion and dispersion simulations.

Commentary by Dr. Valentin Fuster
2002;():95-110. doi:10.1115/IMECE2002-33821.

A stereoscopic particle image velocimetry (PIV) system was used to measure flow within a one-tenth-scale room. The dimensions of the scaled room were 732 × 488 × 274 mm (28.8 × 19.2 × 10.8 in.). The measurements were made under isothermal conditions and water was used as the fluid instead of air. Six equally spaced vertical planes along the length of the room were captured and symmetry was utilized so that measurements were only made on one side of the room. A sample size of 50 pairs of PIV images were collected and averaged to determine average velocity. Turbulent kinetic energy was also calculated from the collected data. The equipment configuration, measurement information and the velocity and turbulent kinetic energy results are presented in this paper. The measurements provide detailed three dimensional velocity profiles that could be used to validate numerical simulations.

Commentary by Dr. Valentin Fuster
2002;():111-118. doi:10.1115/IMECE2002-33860.

This paper presents a study on improvements of multi-zone models for predicting building contaminant distribution by combining a multi-zone model with a Computational Fluid Dynamic (CFD) model. The motivation is to avoid the long computations in the CFD model that are required for predicting concentrations in entire buildings. Two cases are investigated using the combined model and the results are compared to reliable experimental or CFD data. The comparisons show that the combined model provides better results than the multi-zone model alone in one of the cases, while in the other no major improvements were observed. Further investigation and development of the combined model is needed.

Topics: Structures
Commentary by Dr. Valentin Fuster
2002;():119-126. doi:10.1115/IMECE2002-33862.

Multizone network airflow analysis is used to analyze stack and mechanical system effects on the distribution of three representative biological agents in a prototype 40 story building. This approach relies on mass balances to compute airflow and contaminant transfer between the building zones. The analysis considers stack effects caused by cold outdoor temperatures, unintended positive and negative pressurization of the floor on which the release of the agent occurs, and three levels of contaminant removal using a combination filter/UVGI system. The results show that vertical shafts, such as stairwells and elevator shafts provide significant routes for contaminant transfer between floors, even when these floors are served by different air handling systems. Because the air moving through these pathways does not pass through an air handling system, this type of transport is not as easily reduced by filtering. However, commercially available filters were able to reduce contaminant concentrations substantially in zones that receive contaminants primarily due to recirculation through the air handling system.

Commentary by Dr. Valentin Fuster
2002;():127-137. doi:10.1115/IMECE2002-39411.

Proper distribution of conditioned air plays an important role in both human thermal comfort and indoor air quality. Experimental investigations of airflow and temperature distributions for typical indoor environmental conditions are essential but expensive and time consuming. Technological advances in computer hardware and development of computational software in recent years have made numerical simulations of such flow conditions possible. The objectives of this study were to: (1) Evaluate the applicability of a commercial software in conducting numerical simulations of indoor airflow conditions for both isothermal and non-isothermal conditions using different turbulence closure models, and (2) Determine the effects of different grid generation techniques on the numerical results. The computations were performed for a large rectangular geometry room. Conditioned air entered the room through a high sidewall grille located on one side of the wall and exited through a return located on the opposite side of wall. All walls and ceiling were insulated. The floor was heated at a constant heat rate. This paper presents velocity, temperature, and turbulent kinetic energy profiles at various cross-sections. Good agreements between the numerical simulation results and experimental data were achieved.

Commentary by Dr. Valentin Fuster
2002;():139-147. doi:10.1115/IMECE2002-39418.

Wind tunnel simulations and computations with AERMOD were used to investigate the impact of the emission from a proposed gas-turbine heat-recovery plant. The plant will be located near a university and has 80 m hills to the south and east. Seasonal meteorological conditions required by AERMOD were obtained from a regional airport 80 miles from the site. AERMOD was best suited for obtaining 3-hour, 24-hour, and yearly averaged worst conditions and for determining the drainage flow into a small river valley in the general vicinity of the plant. The wind tunnel was well suited for studying the impact of the plume on buildings and the hills surrounding the plant. In general the wind tunnel-measured impact was higher that predicted by AERMOD, but both data sets followed the same trends with higher concentration at sites near the plant when the wind speed increased and as the stack height was shortened. A one-to-one comparison of the predictions was not possible.

Commentary by Dr. Valentin Fuster
2002;():149-156. doi:10.1115/IMECE2002-39451.

There is a need for information on dispersion and infiltration of chemical and biological agents in complex building environments. A recent collaborative study conducted at the Idaho National Engineering and Environmental Laboratory (INEEL) and Bechtel Corporation Research and Development had the objective of assessing computational fluid dynamics (CFD) models for simulation of flow around complicated buildings through a comparison of experimental and numerical results. The test facility used in the experiments was INEEL’s unique large Matched-Index-of-Refraction (MIR) flow system. The CFD code used for modeling was Fluent, a widely available commercial flow simulation package. For the experiment, a building plan was selected to approximately represent an existing facility. It was found that predicted velocity profiles from above the building and in front of the building were in good agreement with the measurements.

Commentary by Dr. Valentin Fuster
2002;():157-170. doi:10.1115/IMECE2002-39622.

Computational fluid dynamics (CFD) simulations were used to predict three-dimensional flow within a one-tenth-scale room. The dimensions of the scaled room were 732 × 488 × 274 mm (28.8 × 19.2 × 10.8 in.) and symmetry was utilized so that only half of the room was modeled. Corresponding measurements were made under isothermal conditions and water was used as the working fluid instead of air. The commercially available software Fluent was used to perform the simulations. Two turbulence models were used: the renormalization group (RNG) k-ε model and the Reynolds-stress model. The CFD setup is presented in this paper, along with the velocity and turbulent kinetic energy results. The simulation results are compared to previously obtained three-dimensional particle image velocimetry (PIV) measurements made within the same scaled room under similar conditions.

Commentary by Dr. Valentin Fuster
2002;():173-181. doi:10.1115/IMECE2002-32185.

Flow-alignment of sheared nematic polymers occurs in various flow-concentration regimes. Analytical descriptions of shear-aligned nematic monodomains have a long history across continuum, mesoscopic and mean-field kinetic models, sacrificing precision at each finer scale. Continuum Leslie-Ericksen theory applies to highly concentrated, weak flows of small molecular weight polymers, giving an explicit macroscopic alignment angle formula dependent only on Miesowicz viscosities. Mesoscopic tensor models apply at all concentrations and shear rates, but explicit “Leslie angle” formulas exist only in the weak shear limit (Cocchini et. al, 90; Bhave et. al, 93; Wang, 97; Rienacker and Hess, 99; Maffettone et. al, 00; Forest and Wang, 02; Forest et. al, 02c; Grecov and Rey, 02), with distinct behavior in dilute versus concentrated regimes. Exact probability distribution functions (pdf’s) of kinetic theory do not exist for highly concentrated nematic states, even without flow, although appealing flow-aligned approximations have been derived (Kuzuu and Doi, 83; Kuzuu and Doi, 84; Semenov, 83; Semenov, 86; Archer and Larson, 95; Kroger and Seller, 95), which offer a molecular theory basis for the Leslie alignment angle. A simpler problem concerns the dilute concentration regime where the unique quiescent equilibrium is isotropic, corresponding to a constant pdf, and whose weak shear deformation is robust to mesoscopic closure approximation (Forest and Wang, 02; Forest et. al, 02c): steady, flow-aligning, weakly anisotropic, and biaxial. The purpose of this paper is to explicitly construct the weakly anisotropic branch of stationary pdf’s by a weak-shear asymptotic expansion of kinetic theory. A second-moment pdf projection confirms mesoscopic model predictions, and further yields explicit Leslie angle and degree of alignment formulas in terms of molecular parameters and normalized shear rate.

Commentary by Dr. Valentin Fuster
2002;():183-191. doi:10.1115/IMECE2002-32186.

It is difficult, if not impossible to quantify LCB in polymers using rheological test methods only. Most of the reported rheological methods are affected by polymer characteristics other than LCB (Molecular weight Distribution (MWD), polymer microstructure, polymer type etc[[ellipsis]]). Poly-Propylene samples having different level of LCB produced by reactive extrusion with Per-Oxi-Dicarbonate have been characterised at strain ratios between 2.5 and 10. Stress signal distortion has been found to be sensitive only to the presence and level of LCB and not to Average Molecular Weight (AMW) and MWD. Quantification of the signal distortion was performed using Fourier transform rheology. As linear visco-elasticity equations are not applicable to LAOS, the approach of Giacomin and Dealy was applied. This considers the stress signal as a Fourier series and enables the calculation of G′n and G″n . LCB has a strong effect on both G′n and G″n , on their ratio and especially on G′ from the first harmonic (G′1 ). Repeatability data (CV) on G′1 and G″1 shows excellent sensitivity (<1%). The technique has been successfully applied to commercially available elastomers (BR and EPDM) enabling comparisons based on LCB level irrespectively of the AMW and MWD. Rapid graphical differentiation between linear and non linear polymers is achieved with stress/strain rate curves (Lissajou figure). The development of this technique provides polymer suppliers and their customers the ability to rapidly assess variations in Long Chain Branching, essential for incoming material and/or production control.

Commentary by Dr. Valentin Fuster
2002;():193-199. doi:10.1115/IMECE2002-32187.

A constitutive relation between the pressure gradient and the seepage velocity has been developed that carries information about the liquid behavior on extension. The relation was developed in two steps. Firstly the pressure drop/flow rate relationship for an ideal pore channel was obtained. Then a capillaric model theory was applied to obtain the sought-for constitutive equation. The proposed relation was validated comparing pressure drop/flow rate results with experimental data obtained in a geometry similar to the one used in the theoretical model. Also, some comparisons with experimental data for a M1 Boger fluid flowing in a model porous medium were performed. The results showed that the proposed relation has good predictions capabilities in a representative range of pressure gradients.

Commentary by Dr. Valentin Fuster
2002;():201-208. doi:10.1115/IMECE2002-32188.

The laminar helical flow of a viscoplastic (or highly shear-thinning) material through the developing region of concentric annular spaces was examined. This physical situation is important in a variety of applications, including the flow of drilling muds through petroleum wells. The velocity, pressure and viscosity fields were obtained by solving the mass- and momentum-conservation equations via a finite-volume method. The Generalized Newtonian Liquid model was adopted as constitutive equation. The Carreau model was employed as viscosity function, whose parameters were obtained via a least-squares to fit to data obtained for a viscoplastic material. Solutions are presented for a wide range of Reynolds and Taylor numbers, within the subcritical regime.

Commentary by Dr. Valentin Fuster
2002;():209-219. doi:10.1115/IMECE2002-32189.

The hydrodynamic theory developed in [31] for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of spheroidal molecular configurations is extended to account for translational diffusion and the related spatial density variation. The new theory augments the added effect of the density variation to the Smoluchowski equation and the elastic stress. It accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from the rodlike liquid crystal at large aspect ratios to the discotic one at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations.

Commentary by Dr. Valentin Fuster
2002;():221-226. doi:10.1115/IMECE2002-32190.

A numerical method based on the distributed Lagrange Multiplier method (DLM) [2,8] is developed for direct simulations of electrorheological (ER) liquids subjected to spatially varying electric fields. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method. The point-dipole approximation [6] is used to model the electrostatic forces acting on the polarized particles. The code is verified by performing a convergence study that shows that the results are independent of mesh and time step sizes. In a spatially nonuniform electric field the particles move to the regions where the magnitude of electric field is locally maximum when the particle permittivity is greater than that of the liquid. On the other hand, when the particle permittivity is smaller than that of the liquid the particles move to the regions of local minimum of electric field.

Commentary by Dr. Valentin Fuster
2002;():227-234. doi:10.1115/IMECE2002-32191.

Over a range of 70 < Rea < 9600, 7 < Pra < 130, 0 < ∃ < 0.12 and 0.7 < n < 1, circumferential wall temperatures for air-water and air-aqueous polymer (viscoelastic) solution flows over a horizontal cylinder were measured experimentally. The 2.5-cm-diameter and 7.5-cm-length cylinder was heated by passing direct electric current through it. The peripherally averaged heat transfer coefficient for relatively dilute viscoelastic-air solutions, at any fixed flow rate of liquid phase, increases with ∃. Such increase is more pronounced at lower flow rates of liquid phase. For relatively more elastic solutions, the two-phase heat transfer decreases with increasing ∃. Such reduction is more pronounced at higher flow rates of liquid phase. A new correlation is proposed for predicting the Nusselt number for air-viscoelastic fluid flows over a heated cylinder in cross flow.

Commentary by Dr. Valentin Fuster
2002;():235-238. doi:10.1115/IMECE2002-32195.

The mesquite seed gum (Prosopis sp.) represents an alternative application in the food industry, due to its structural likeness with other galactomannans used at the moment. The information about the properties of mesquite seed gum is scarce, for this is important to known the rheological properties of this biopolymer and its interactions with other polymers for seeing future applications. The aim of this work was study the rheological behavior of mesquite seed gum and their effects in arabic and gellan gum mixtures. They were prepared aqueous dispersions according to a Simplex-Centroid design, being obtained gum combinations of total concentration of 1% from mesquite-arabic, mesquite-gellan, arabic-gellan and mesquite-arabic-gellan, the pH from the dispersions were adjusted to 4, 5 and 6. The mixtures as well as the individual biopolymers were dispersed to ambient temperature, and later heated during 20 minutes at 90 °C and cooling at 25 °C. The rheological studies were made using an Haake RV2 viscometer. The statistical analysis showed differences (α = 0.05) among the rheologic value for mixtures at different pH. The mixtures showed a non-Newtonian behavior, type pseudoplastic flow (shear thinning) and showed high viscosities to low shears rates (100 s−l ) in all the cases. The tendency of mixtures with two or three components showed an antagonistic effect in the viscosity. Particularly the mesquite seed gum suffers an antagonistic effect in the viscosity when it was mixed with the arabic and gellan gums, being observed decreases from a 8 until 45%, below the control.

Commentary by Dr. Valentin Fuster
2002;():239-248. doi:10.1115/IMECE2002-32197.

This paper reports the first measurements of the effective tensile strength (or ‘cavitation threshold’), Fc , of degassed samples of a commercial ‘multigrade’ oil over a range of temperatures, T, representative of those encountered under its normal operating conditions (in the range 20°C ≤ T ≤ 140°C). Also reported are the values of Fc obtained for Newtonian silicon oils over a range of shear viscosities. In the experimental apparatus used in this work, samples of liquid are subjected to dynamic stressing involving a rapid pressure-tension cycle (this being a feature of conditions experienced by a lubricant within a dynamically-loaded journal bearing). Moreover, the method used herein to estimate Fc avoids reliance upon direct measurements of substantial dynamic negative pressures using transducers which are designed for use in the range of positive pressures.

Commentary by Dr. Valentin Fuster
2002;():249-255. doi:10.1115/IMECE2002-32198.

The gas penetration of a long bubble through a viscoelastic fluid in a tube was studied. Experiments were carried out for two Newtonian and five polymeric solutions to investigate the relation between the coating film thickness and rheological properties of the test fluids. The polymeric solutions are viscoelastic fluids having shear-thinning viscosity. A bubble of air was injected into a tube filled with a test fluid to form hydrodynamic coating on a tube wall. The film thickness was evaluated by hydrodynamic fractional coverage m. The fractional coverage was characterized using the capillary number Ca and the Weissenberg number Wi. For viscoelastic fluids, Ca and Wi were evaluated considering the shear-thinning viscosity. Two kinds of representative shear rate were used for the evaluation of Ca and Wi. The dependence of m on Ca in viscoelastic fluids was different from that of the Newtonian case. The film was thinner than that of the Newtonian case at the same Ca when Wi was small, i.e. the viscous property was dominant. The shear-thinning viscosity had a role to make the film thin. On the other hand, the film tended to be thicker than the corresponding Newtonian results at large Wi because of normal stress effect.

Commentary by Dr. Valentin Fuster
2002;():257-263. doi:10.1115/IMECE2002-32228.

Liquid crystal is one of homogeneous ER (Electrorheological) fluids in some range of temperature. In the present experiment a liquid crystal mixture is used. The responses of the pressure drop are examined when the liquid crystal mixture flows between two parallel-plate electrodes for the constant flow rates. When the voltages are applied on the liquid crystal mixture and removed, the pressure responses of the inlet electrodes are measured with the pressure transducer. At same time, the liquid crystal mixture between the transparent electrodes made of glass is visualized with the video camera investigate the time history of the director of the liquid crystal mixture. The AC voltages are also used to investigate dependence of the liquid crystal mixture on the frequency the voltages. Outlet of the flow channel with two parallel-plate electrodes is atmosphere. Relation between the flow visualization results and the changes of pressure drop investigated especially for transient period. On the other hand, the pulse-wave voltages are added to the electrodes to control the pressure drop using the pulse width modulation or the pulse frequency modulation. In the present study the flow rates change from 0.001cc/sec (velocity is lmm/sec) to 0.003cc/sec and the electric field intensity is from 0.2kV/mm to lkV/mm. The gap of the electrodes is 0.2mm.The isotropic-nematic transition is 90.0°C and smectic-nematic transition is −44.0°C for the liquid crystal mixture. The open-loop test facility the liquid crystal is set in a pyrostat to keep the temperature constant.

Commentary by Dr. Valentin Fuster
2002;():265-270. doi:10.1115/IMECE2002-32229.

The flow of surfactant solutions between two coaxial cylinders was investigated using the laser-induced-fluorescence flow visualization technique to clarify the effect of drag-reducing additives on the formation process of Taylor cells in Taylor-Couette flow. Test fluids were Ethoquad O/12 10, 50 and 100 ppm surfactant solutions. In the Taylor number range of, 1.2×105 ≤ Ta ≤ 7.1×105 , tap water and 10 ppm surfactant solution flows consisted of Taylor vortices and much smaller Görtler vortices at the rotating inner cylinder wall. However, in 50 and 100 ppm surfactant solutions, Taylor vortices are not apparent and Görtler vortices are collapsed. Measurement of the wavelength of Görtler vortices led to the conclusion that surfactant solutions have a stabilizing effect on Görtler instabilities. This effect depends on the concentration of surfactant solutions, and becomes considerable with increasing acceleration of the rotating inner cylinder. By considering the experimental results for the surfactant solutions without counterions, in which Taylor cells were not formed, it was shown that the increase in the local field viscosity based on the shear-induced structure of the surfactant solutions has a stabilizing effect on Görtler instability.

Topics: Surfactants
Commentary by Dr. Valentin Fuster
2002;():271-275. doi:10.1115/IMECE2002-32230.

We propose a model for isothermal mass transport into immiscible complex fluids. The interface is described by two, space and time dependent, structural variables: a scalar Q(r ,t) denoting the interfacial area density and a traceless symmetric second order tensor q (r ,t) accounting for the shape anisotropy. The mass flux expression includes new contributions attributed to the dynamical changes of the interface. The diffusion-morphology coupling is found to influence both the mass transfer and the dynamics of the interface. The former exhibits non-Fickian behavior while the latter undergoes interfacial deformations that affect both its size and shape, creating internal stresses at the same time.

Topics: Mass transfer
Commentary by Dr. Valentin Fuster
2002;():277-281. doi:10.1115/IMECE2002-32231.

A ferrofluid is a suspension of ferromagnetic spherical particles in a base liquid (1), and is well known as a functional fluid which responds to an external magnetic field to give a large increase in the viscosity. Such a significant increase in the viscosity is due to the fact that chain-like clusters are formed owing to magnetostatic interactions between particles in an applied magnetic field. The microstructure formation offers a large resistance to a flow field that gives rise to a significant increase of the apparent viscosity (2).

Commentary by Dr. Valentin Fuster
2002;():283-289. doi:10.1115/IMECE2002-32232.

An analysis of heat transfer in pipe-flow is presented for the cases in which viscoelastic properties of the fluid induce secondary flows in no-circular tubes, thus enhancing the tranversal transport capacity of the flow. It is used the Phan-Thien-Tanner (PTT) viscoelastic model, and the flow is assumed steady and laminar. The velocity field is first determined through a technique previously developed by the authors, and the energy equation is solved afterward for the temperature field for conditions of constant wall temperature and constant longitudinal temperature gradient. Perturbation analysis is applied around the relaxation time as parameter, wherefrom all orders of velocity and temperature are analytically found up to third order. Plots of results for triangular and square tubes are presented, followed by a discussion of the relevant findings related to interactions among the main variables generated by viscoelastic fluid behaviour.

Commentary by Dr. Valentin Fuster
2002;():291-295. doi:10.1115/IMECE2002-32233.

Secondary flows of Phan-Thien-Tanner fluids in channels formed by two intersecting walls, and driven by a pressure gradient parallel to the intersection line, are studied by means of perturbation analysis, where the perturbing parameter is the relaxation time. The velocity field is analysed in relation to the opening angle and distance from the corner within the fluid region. An analytically exact solution is found at 0(λ3 ), through the mathematical structure of which is possible to draw some general and important conclusions about the dynamics of the transversal flow. Such results are of potential interest in the design of devices aimed at exploiting the transport capacity of secondary flows.

Commentary by Dr. Valentin Fuster
2002;():297-308. doi:10.1115/IMECE2002-32235.

A general model of generalized linear thermo-viscoelasticity for isotropic material is established taking into consideration the rheological properties of the volume. As special cases the corresponding equations for the coupled thermo-viscoelasticity and the generalized thermo-viscoelasticity with one (Lord-Shulman theory) or with two relaxation times (Green-Lindsay theory) are obtained. The cases of thermo-viscoelasticity ignoring the rheological properties of volume can be obtained from the given model. The equations of the corresponding thermoelasticity theories result from the given model as special cases. A formulation of the boundary integral equation method, fundamental solutions of the corresponding differential equations are obtained and the dynamic reciprocity theorem is derived for this general model. Generalizations of Somiliana’s –Green and Maysels formulas are obtained. An example illustrating the BIE formulation is given. Special emphasis is given to the representation of primary fields, namely temperature and displacement.

Commentary by Dr. Valentin Fuster
2002;():309-320. doi:10.1115/IMECE2002-32236.

The rheological properties and friction pressure losses of several fluids that are most commonly used as well drilling, completion, and stimulation fluids have been investigated experimentally. These fluids include polymeric fluids – Xanthan gum, partially hydrolyzed polyacrylamide (PHPA), guar gum, and hydroxyethyl cellulose (HEC), bentonite drilling mud, oil-based drilling mud, and guar-based fracturing slurries. Rheological measurements using a Bohlin CS 50 rheometer and a model 35 Fann viscometer showed that these fluids exhibit shear thinning and thermal thinning behavior except the bentonite drilling mud whose viscosity increased as the temperature was raised. Flow experiments using a full-scale coiled tubing test facility showed that the friction pressure loss in coiled tubing is significantly higher than in straight tubing. Since the polymeric fluids displayed drag reducing property, their drag reduction behavior in straight and coiled tubings was analyzed and compared. It was found that the drag reduction (DR) in coiled tubing is much lower than that in straight tubing. Plots of drag reduction vs. generalized Reynolds number indicate that the drag reduction in coiled tubing was not affected by polymer concentration as much as in straight tubing. The onsets of turbulence and drag reduction in coiled tubing were significantly delayed as compared with straight tubing. The effect of solids content on the friction pressure losses in coiled tubing is also briefly discussed.

Topics: Fluids , Drilling
Commentary by Dr. Valentin Fuster
2002;():321-329. doi:10.1115/IMECE2002-32237.

In complex porous media we often notice a percolation phenomenon [KIR 71] [GRI 89]. Usually these media present discontinuous characteristics and a random space distribution [LET 00] [BIR 95]. There results that the classical models based on the resolution of a partial differential problem become inefficient because we have non-derivable function [MAU 01]. Statistical approaches based on the resolution of partial differential problems pose notably the questions concerning the continuity of the functions representing the physical properties of the medium. In this work we propose to study a numerical model of porous media based on a mixture of 2 components in a percolation context. In practice, the main difficulty is based on the complex physical properties. We present also a model of homogenization. Our numerical model is based on the Finite Element approach.

Commentary by Dr. Valentin Fuster
2002;():331-335. doi:10.1115/IMECE2002-32238.

Ultrasonic signals can be used to interrogate many forms of two-phase systems, dense slurry-laden and three-phase suspensions. This paper describes using ultrasonic signal reflection at a fluid-sensor interface to characterize fluid and slurry density and viscosity. The sensor consists of a series of transducers mounted on a wedge with the base of the wedge in contact with the liquid. Ultrasonic beams, striking the wedge base at several angles, are reflected at the base-liquid interface to the receive transducers. The amount of reflection at this interface depends upon the density of the liquid, the speed of sound in the liquid, and the wedge parameters. The response of a shear wave transducer, in conjunction with a density measurement, is used to determine the viscosity. The sensor can be mounted in a pipeline configuration or submerged in a tank for process control of food products. Novel features include: the small size of the probe and the sensor robustness. Performance is not affected by fluid flow rate, entrained air, or vibration. Experimental measurements of the density and viscosity for fluids and slurries are presented.

Commentary by Dr. Valentin Fuster
2002;():337-344. doi:10.1115/IMECE2002-32582.

The results of an experimental investigation aimed to study both the rheological and fluid dynamic behaviour of two kinds of fruit purees at different pulp concentrations are presented in this work. An experimental setup based on the rectilinear pipe viscometer principle was used for a preliminary rheological investigation of the analyzed products. By applying either the classical Rabinowitsch and Mooney or the recent Thikonov method of regularization of integral equations, these products could reliably be considered as purely-viscous time-independent fluids. The laminar motion was described by means of the well known Metzner and Reed method while the corresponding resistance laws for turbulent motion were modeled by using the Dodge and Metzner method. The comparison of the point onset of turbulence against the ones obtained by means of the Mishra and Thripati and Hanks formulas would, however, suggest that in transitional regime the viscoelastic effects could have non-negligible influence on the dynamics.

Topics: Motion , Turbulence , Pipes
Commentary by Dr. Valentin Fuster
2002;():347-356. doi:10.1115/IMECE2002-39444.

NASA’s Glenn Research Center has been selected to lead development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability. The NASA Hall thruster program currently supports a number of tasks related to high power thruster development for a number of customers including the Energetics Program (formerly called the Space-based Program), the Space Solar Power Program, and the In-space Propulsion Program. In program year 2002, two tasks were central to the NASA Hall thruster program: 1.) the development of a laboratory Hall thruster capable of providing high thrust at high power; 2.) investigations into operation of Hall thrusters at high specific impulse. In addition to these two primary thruster development activities, there are a number of other on-going activities supported by the NASA Hall thruster program. These additional activities are related to issues such as thruster lifetime and spacecraft integration.

Topics: Engines
Commentary by Dr. Valentin Fuster
2002;():357-366. doi:10.1115/IMECE2002-39445.

Magnetogasdynamics (MGD) has the potential to lift many of the constraints presently inhibiting sustained hypersonic flight and affordable access to space. Given the difficulty of ground-testing under the expected harsh conditions, numerical methods can provide insight into the physical phenomena, and thus complement experimental investigations in the development of future concepts. This paper describes the status of an effort to develop a high-fidelity, fully three-dimensional method to explore MGD flow control in complex configurations. The theoretical model includes several non-ideal effects and takes recourse to a blend of first principles and phenomenological approaches to enhance simulation efficiency. Boundary conditions are summarized and sample verification exercises are presented. Exploratory calculations on a reentry vehicle and flow-through scramjet flowpath with MGD-bypass demonstrate the versatility of the approach and yield insight into dominant flow control mechanisms.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2002;():369-373. doi:10.1115/IMECE2002-33030.

This paper is considering issues connected with parallelization of Direct Simulation Monte Carlo (later referred as DSMC). The method is applied to simulate gas flow in micro-channels. The general algorithm of DSMC can be divided into two steps: deterministic motion of particles and stochastic part, related to collisions of particles. This division also reflects in the way, how DSMC have to be parallelized. For the first part domain decomposition techniques are important, while the second step heavily depends on the parallel random number generator.

Commentary by Dr. Valentin Fuster
2002;():375-382. doi:10.1115/IMECE2002-33040.

A parallel computing methodology is presented for the direct numerical simulation of turbulent flows induced by pressure gradients and induction forces in channels. The numerical algorithm is based on the high-order-finite-difference (HOFD) scheme, which has been shown to possess the spectral-like accuracy but with superior computational efficiency and thus is ideally suited for computationally intensive numerical studies such as direct numerical simulation of turbulence. The computational efficiency is further enhanced using parallel computers. The parallel implementation and computational performance are discussed and numerical results using the parallel algorithms for direct numerical simulation of pressure gradient driven in parallel-plate channels and magnetically driven turbulent flows in induction channels are presented.

Commentary by Dr. Valentin Fuster
2002;():383-388. doi:10.1115/IMECE2002-33045.

The development of commodity-off-the-shelf computer hardware components has allowed for the trend in high performance computing away from computer-system vendor proprietary hardware. A Beowulf computer system is a high performance computer assembled from commodity-off-the-shelf hardware and uses application programming interface libraries and open source operating systems to create a unified computing environment. In this paper, a Beowulf computer system is described and a performance benchmarking exercise is presented. The simulation is a benchmark problem relevant to hydrocode simulations and specifically simulates the high-speed impact and penetration of a long rod. Through this simulation study and a comparison to similar simulations performed on other computer systems, the price/performance advantage of a Beowulf system is demonstrated.

Topics: Computers
Commentary by Dr. Valentin Fuster
2002;():389-398. doi:10.1115/IMECE2002-39388.

The development and validation of a parallel unstructured non-nested multigrid method for simulation of unsteady incompressible viscous flow is presented. The Navier-Stokes solver is based on the artificial compressibility method (ACM) [10] and a higher-order characteristics-based finite-volume scheme [8] on unstructured multigrids. Unsteady flow is calculated with an implicit dual time stepping scheme. The parallelization of the solver is achieved by a multigrid domain decomposition approach (MG-DD), using the Single Program Multiple Data (SPMD) programming paradigm and Message-Passing Interface (MPI) for communication of data. The parallel codes using single grids and multigrids are used to simulate steady and unsteady incompressible viscous flows over a circular cylinder for validation and performance evaluation purposes. Speedups and parallel efficiencies obtained by both the parallel single-grid and multigrid solvers are reasonably good for both test cases, using up to 32 processors on the SGI Origin 2000. A maximum speedup of 12 could be achieved on 16 processors for the unsteady flow. The parallel results obtained agree well with those of serial solvers and with numerical solutions obtained by other researchers, as well as experimental measurements.

Commentary by Dr. Valentin Fuster
2002;():401-405. doi:10.1115/IMECE2002-33556.

This paper presents an experimental investigation of field amplified sample stacking (FASS) with micron resolution particle image velocimetry (μPIV). The preliminary experiments reported in this work show particle velocity fields in electrokinetic flow in a glass microchannel with a single buffer-buffer interface. The buffer-to-buffer conductivity ratio is 10. Stacking of latex microspheres (i.e., increases in their number density) in the presence of a background electroosmotic flow is demonstrated. The generation of an internal pressure gradient is quantified using μPIV. This work is part of an ongoing study of the spatial and temporal development of the velocity and concentration profiles of FASS systems.

Commentary by Dr. Valentin Fuster
2002;():407-414. doi:10.1115/IMECE2002-33559.

The magneto hydrodynamic fluidic network’s basic building blocks are conduits equipped with two electrodes positioned on opposing walls. The entire device is either subjected to an external uniform magnetic field or fabricated within a magnetic material. When a prescribed potential difference is applied across each electrode pair, it induces current in the liquid (assumed to be a weakly conductive). The current interacts with the magnetic field to produce a Lorentz force that is perpendicular to both the directions of the current and the magnetic field. Analogously with electric circuits, by judicious application of the potential differences at various branches, one can direct liquid flow in any desired way and rate without a need for mechanical pumps or valves. By equipping the network branches with additional, interior electrodes, the branches double as stirrers capable of generating chaotic advection. The paper describes the basic building blocks for such a network, the operation of these branches as stirrers, a general theory for the analysis and control of fluidic magneto-hydrodynamic networks, and an example of a network fabricated with low temperature, co-fired ceramic tapes.

Topics: Networks
Commentary by Dr. Valentin Fuster
2002;():415-418. doi:10.1115/IMECE2002-33563.

This paper documents the scalar imaging of an electrokinetic flow instability that is directly relevant to microfluidic systems that aim to handle and analyze heterogeneous sample streams. The instability occurs in simple T-junctions where two streams of different ionic concentration flow into a common channel. Using neutral dye visualizations, general qualitative behavior of the instability is documented including the formation of a wave in the stream/stream material line that originates at the junction of the two channels and propagates downstream. Several quantitative properties of this phenomenon are measured including wave speed and the extent of the perturbation boundary. This work is part of an ongoing project to identify the physics of this instability and determine the regime of stability, with an ultimate goal of developing methods to either enhance or suppress the instability.

Commentary by Dr. Valentin Fuster
2002;():419-423. doi:10.1115/IMECE2002-33564.

The Ratcheting Electrophoresis Microchip (REM) is a microfluidic device for electrophoretic separation of biomolecules such as DNA and proteins. By using thousands of electrodes along the length of a microchannel, the REM separates molecules using low applied voltages (∼1 V) in short times (< 1 minute). This paper describes the microfabriation of the REM and initial testing results. Parallel arrays of platinum electrodes are fabricated on a silicon chip with a pitch of 10 μm. Two types of channels are fabricated: silicon nitride channels fabricated on the chip and poly(dimelthylsiloxane) (PDMS) channels fabricated separately and attached to the chip. Initial testing shows partial success with the PDMS channels and promis ing results for the silicon nitride channels.

Commentary by Dr. Valentin Fuster
2002;():425-430. doi:10.1115/IMECE2002-33625.

This papers presents the analytical solution of the flow distribution along a porous membrane which is between two parallel microchannels, a configuration of increasing importance in microsystems for DNA sequencing, catalytic chemistry, and in micro heat exchangers. The modeling approach presented in the paper is inspired from thin film lubrication theory and would be applicable for a wide range of low Reynolds number, pressure-driven microfluidic configurations.

Commentary by Dr. Valentin Fuster
2002;():431-437. doi:10.1115/IMECE2002-33628.

A parametric description of two existing types of planar fixed-geometry micropump valves, the nozzle-diffuser and the Tesla-type, can be accomplished with surprisingly few parameters. The planform shape for the former requires only four parameters and the latter only five. Following this observation, a new valve type, the Tesser valve, was created having features of both the Tesla-type and nozzle-diffuser that required only two additional parameters, for a total of seven. Our overall goal is to utilize formal optimization techniques and computational fluid dynamics (CFD) with a experimental testing program to achieve valve efficiency that would be very difficult if not impossible to determine empirically. In this study we utilized two-dimensional computations that revealed a strong dependence of diodicity on Reynolds number in the range common for current micropump designs. The study also showed that the Tesser valve was superior at low Reynolds number 10 < Re < 100, and the Tesla-type valve superior at higher Reynolds number 100 < Re < 2000.

Commentary by Dr. Valentin Fuster
2002;():439-448. doi:10.1115/IMECE2002-33630.

Theory, manufacturing and experimental results of acoustically generated micromachined jet arrays for micropropulsion applications are presented. A reduced order theoretical analysis is found to be an accurate performance predictor. Scaling laws derived from the theory suggest the performance benefits derived by reducing the geometric size of the resonators, specifically the application of MEMS technologies. A novel manufacturing method is employed to construct the devices, incorporating an electrostatically actuated membrane to drive the acoustic jets. Experimental results of the MEMS devices demonstrate a structurally sound design, and a performance commensurate with expectations.

Commentary by Dr. Valentin Fuster
2002;():449-458. doi:10.1115/IMECE2002-33640.

In this paper we address the problem of assembling several different microfluidic devices, often made from different materials, into a hybrid packaged system. The focus will be on integration of silicon microfluidic die into larger hybrid systems. Details of three different approaches are presented: 1) a plastic flow manifold with tape die attach, 2) multiple capillary die insertion utilizing PDMS (Polydimethylsiloxane – silicone adhesive) for sealing and structural support, and 3) die attachment to a glass flow manifold utilizing anodic bonding. The unique tools required for each of these three techniques will be described. Sealed microfluidic connections (>10 ATM pressure) between silicon microfluidic chips (die) and flow manifolds are demonstrated.

Commentary by Dr. Valentin Fuster
2002;():459-464. doi:10.1115/IMECE2002-33644.

We present a CMOS-compatible method of fabricating burried channels within bulk single-crystal silicon serving as the substrate of CMOS circuitry. The channels were designed to provide a compact, forced convection heat transfer liquid cooling approach to microprocessor and integrated circuit thermal management. The baseline fabrication process consumers 8–10% of front-side surface area and serves as a foundation for incorporation of buried-channel cooling with CMOS electronics. Channels were fabricated with diameters ranging from 43–92 μm with sacrificial surface area trenches 10 μm wide. A microchannel heat transfer solution was designed, simulated, and tested with cooling of up to 21 W/cm2 . Compatibility with CMOS electronics was investigated by evaluating the post-process transistor performance of a simple oscillator circuit.

Commentary by Dr. Valentin Fuster
2002;():465-468. doi:10.1115/IMECE2002-33648.

Micro thermal management devices using bubble in microchannel are under development. The heat removal mechanism of this device consists of phase change and forced convection which occur simultaneously and harmonically. Bubble expension in horn-shaped microchannel gives directional purnping by low-energy consumption. Several kinds of chips are built and tested. The uncontrollable phenomena of bubbly flow in microchannels and the key factors for further improvement are discussed.

Commentary by Dr. Valentin Fuster
2002;():469-475. doi:10.1115/IMECE2002-33667.

The paper introduces a new viscous pump, called the spiral pump, which targets surface micromachining, and outlines its implementation in five levels of polysilicon using Sandia’s Ultraplanar Multilevel MEMS Technology (SUMMiT). For the purpose of analyzing the flow field in the pump, the spiral channel is approximated as an equivalent straight channel. After demonstrating the validity of this approximation for typical design, the paper presents a lubrication solution of the flow field in the channel, which is used to relate the flow rate, torque and power to rotation rate and pressure head. Experimental flow rate versus pressure data obtained from a scaled up spiral pump prototype are compared with analytical predictions, highlighting needed research efforts in modeling and analysis of the spiral pump.

Commentary by Dr. Valentin Fuster
2002;():477-485. doi:10.1115/IMECE2002-33674.

The performance of a selective group of mini and micro-pumps has been evaluated for use in gas phase detection for the Micro-Chem-Lab™. Our major assessment criteria are: flow rate, pressure drop across the pump, and electrical current drawn by the pump. Two pumping configurations have been investigated: (1) upstream pumping to build up pressure head and (2) downstream pumping to draw vacuum. Four mini-pumps (T-Square, SP 250 EC, SP 135 FZ-4, and KNF Neuberger) have been studied. Each of these pumps has been tested to determine whether they meet our requirements of high head pressure, high flow rate, and low power consumption. We have also assessed different mechanisms for pumping gas in micro-domains — specifically, a valveless diffuser/nozzle micro-pump, a LIGA diaphragm micro-pump and a micro drag pump. However our preliminary findings reveal that these micro-pumps do not meet our minimal requirements for use in the μChemLab™.

Topics: Chemistry , Micropumps
Commentary by Dr. Valentin Fuster
2002;():487-492. doi:10.1115/IMECE2002-33679.

Sintered glass electroosmotic pumps have been fabricated that provide maximum flow rates and pressure capacities exceeding 14 ml/min and 1.4 atm, respectively, at 150 V, with an active pumping volume of less than 2 cm3 . These compact devices with no moving parts have the potential to impact a variety of applications including microelectronics cooling systems and bioanalytical applications. We present here a preliminary a study of the response of the pumps to changes in fluidic load, including their short-term transient performance. A 0.5 mM borate buffer (pH = 9.2) is used to stabilize pump performance, with nearly optimal flow rate capacity. The experiments are conducted for working electrolytes of varying ion concentration. These performance characteristics are critical to applications that aim to use feedback control of flow rate and pressure over varying conditions.

Topics: Glass , Pumps
Commentary by Dr. Valentin Fuster
2002;():493-500. doi:10.1115/IMECE2002-33682.

Since microfabrication techniques are typically planar processes, microchannel flows typically have significant predevelopment due to the upstream reservoir having the same height as the microchannel. The main concerns of the current study are categorized into finding the effects of typical microchannel geometry on the velocity entrance length in the laminar flow regime and providing the turbulence transitional Reynolds number range using the details of the velocity profile rather than global measurements of pressure drop. A rectangular micro-channel of aspect ratio ∼2.65 and the hydraulic diameter 380μm was used in this study. Micro particle image velocimetry measurement was performed to measure the velocity profiles. The entrance length is reduced about 45% and the transitional velocity profile is measured at Re=2900. The velocity profiles do not show deviation from the fully developed laminar flow profiles up to Re=2100. Related to the flow transition, the close resemblance between the correlation function peak broadening and the turbulence intensity is observed.

Commentary by Dr. Valentin Fuster
2002;():501-509. doi:10.1115/IMECE2002-39385.

Progress in the development of a micro heat engine is presented. The prototype micro heat engine is an external combustion engine, in which thermal power is converted to mechanical power through the use of a novel thermodynamic cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. The design, well suited to photolithography-based batch fabrication methods, is unlike any conventionally manufactured macro-scale engine. In this paper, the design, fabrication and preliminary testing of a working prototype are discussed. The operation of the engine and its key component, the piezoelectric membrane generator is presented. For the first time, the production of electrical power by a dynamic micro heat engine is demonstrated.

Commentary by Dr. Valentin Fuster
2002;():513-519. doi:10.1115/IMECE2002-33675.

Experiments were conducted to better understand the flow physics associated with axial flow mixers in pipes. Specifically, the dependence of the downstream mixing evolution on the velocity ratio of the secondary to primary stream was explored. Experiments were conducted in a 25.4 mm diameter water pipe flow loop (25,700 ≤ RD ≤ 28,500), in which a fluorescein dye was coaxially injected. The injection tube diameter was 1.5 mm. Three velocity ratios, VR = 0.5, 1.0 and 2.0 were explored, where VR = Vjet /Vmain . The present results indicate that the effects of velocity ratio on the mean concentration are primarily evident in the near-field flow downstream of the injector, while concentration variance measurements indicate a primary influence at intermediate axial locations. Analysis of higher order moments and flow visualizations suggest that these influences are associated with the injected flow conditions. Two-dimensional LIF analysis of the coherent jet breakup region showed an instability in this transition related to injector flow Reynolds number. The present concentration measurements do not indicate the exponential variance decay commonly used for modelling mixing in pipes. Far field data exhibit low wavenumber motions as predicted by the recent theory of Guilkey et al. (1997).

Commentary by Dr. Valentin Fuster
2002;():521-528. doi:10.1115/IMECE2002-33691.

A significant portion of casting defects in the Lost Foam Casting process can be traced back to a lack of consistency in the Expandable Polystyrene (EPS) foam pattern. The present study focuses on determining the cause of EPS foam pattern irregularities through the characterization of the two-phase flow of an EPS bead injector. The process variables studied during this experiment include fill time, fill pressure, EPS bead canister pressure, and fill hose diameter. It was found that the air flow rate under vented EPS bead canister condition using a 1.9 cm (3/4 inch) diameter fill hose increases 33% from a 276 kPa (40 psig) fill pressure to a 552 kPa (80 psig) fill pressure, and the EPS bead mass per cycle for a three second fill time increased 28% from a 276 kPa fill pressure to a 552 kPa fill pressure. The average EPS bead mass per cycle for a pressurized canister and a 1.9 cm diameter fill hose increased 71% from 55.22 grams for a 28 kPa EPS bead canister pressure to 80.21 grams for a 83 kPa EPS bead canister pressure at a fill pressure of 276 kPa. It was also discovered that the air flow rate under pressurized EPS bead canister condition is not a strong function of fill pressure but instead strongly depends on EPS bead canister pressure. The EPS bead mass per cycle for a 1.27 cm diameter fill hose exhibited a lower EPS bead mass per cycle than that for a 1.9 cm diameter fill hose for both the vented and pressurized canister conditions; however, the air flow rates and tip pressures observed for a 1.27 cm (1/2 inch) diameter fill hose showed similar behavior to those for a 1.9 cm diameter fill hose.

Commentary by Dr. Valentin Fuster
2002;():529-535. doi:10.1115/IMECE2002-33696.

Experiments were conducted on the flow field start up behavior of a gelled waxy oil in a pipeline. A simulant fluid was used to mimic the low temperature rheology of crude oil. The break down of the gelled simulant fluid was studied during different startup conditions. It is shown that the “failure mode,” or manner and location in which the gelled simulant fluid breaks down, is closely related to both the temperature of the gel and the cooling time prior to pressurization. Flow visualizations indicate that for higher temperatures, and long cooling times, exists a weaker gel strength and failure occurs near the centerline of the pipe. Lower temperatures and long cooling times result in the breakdown of the gel at the pipe wall. Shorter cooling times result in a weak centerline gel strength, and results in gel failure near the centerline of the pipe. Pressure and temperature data were acquired at seven locations along the length of the test section, and these data were correlated to the velocity field, measured using Particle Image Velocimetry. Combined with rheology measurements, these data, allowed for shear stress estimates to be made. For the parameter ranges explored, the results exhibit three different failure modes, each associated with a different set of initial conditions. A critical temperature existed above which one failure mode was encountered and below which another failure mode was found. A third failure mode was associated with a cross-section that did not have a uniform radial temperature profile.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2002;():537-542. doi:10.1115/IMECE2002-39626.

Experiments for this study were designed to understand gas dispersion in the presence of surface mounted obstacles. To this end, model field experiments were conducted in a compact barrel array employing a spatial distribution of concentration sensors. Specific aims were to explore the effects of atmospheric stability and plume source initial conditions on the plume dispersion through the barrel array. The present results indicate a relaxation towards Gaussian behavior along the plume centerline. The rate of this Gaussian-like behavior is dependent upon atmospheric stability conditions. Plume dispersion through the array appears to be independent of source initial conditions under neutrally stable conditions.

Commentary by Dr. Valentin Fuster
2002;():543-549. doi:10.1115/IMECE2002-39627.

A combined wind tunnel, field measurement, and numerical simulation strategy was used to obtain estimates of the effects of canyon wind flow over proposed building arrays on the Hill Air Force Base (HAFB) runway. As part of this effort, simplified building configurations in the wind tunnel were utilized to optimize computation parameters, as well as gain insights regarding the gross features associated with the proposed building configurations. The field data were used to provide realistic inflow conditions to the numerical simulations. The simulations were then utilized to predict flow fields over the HAFB runway for a number of proposed building configurations. Results from the study, indicated that building configurations primarily oriented transverse to the flow direction showed a persistence of momentum deficit and increased turbulence at large downstream distances. The present solution strategy is shown to constitute a cost effective means of addressing complex applied wind engineering problems with the capability of overcoming Reynolds number and geometric similarity problems.

Commentary by Dr. Valentin Fuster
2002;():553-556. doi:10.1115/IMECE2002-33740.

In most of polymer processings, such as injection molding and extrusion, materials are subjected to high deformations. In order to study nonlinear viscoelastic properties, it is necessary to have an instrument to generate high shear rates. A new sliding plate rheometer incorporating shear stress transducer has been developed. This rheometer has been equipped with a robust servohydraulic linear actuator which can generate shear rates and frequencies up to 900 (1/S) and 500 (Hz) respectively, compared with maximum 500 (1/S) and 100 (Hz), used in latest researches. Using this system, a wider range of nonlinear viscoelasticity can be investigated.

Commentary by Dr. Valentin Fuster
2002;():557-559. doi:10.1115/IMECE2002-33741.

Air-jet filling insertion is the most used techniques in the textile industry. In this process the air flow provides the necessary propelling force to the yarn. Dynamic analysis of air flow in this process was studied experimentally in this work. In Part I we present the results of experimental measurements of pressure losses both in the tube-guided and in the profiled reed simulators.

Commentary by Dr. Valentin Fuster
2002;():561-565. doi:10.1115/IMECE2002-33742.

Air-jet filling insertion is the most popular way of insertion systems in weaving. The heart of the air-jet filling insertion is the air flow, which provides the necessary propelling force for the yarn. In this work, the characteristics of airflow in air-jet filling insertion are discussed. The procedure and experimental system that is developed at Auburn University to measure the air flow characteristics is described.

Commentary by Dr. Valentin Fuster
2002;():567-572. doi:10.1115/IMECE2002-33782.

Water constitutes an attractive manufacturing tool It is readily available and clean. The waterjets are conventionally used for surface cleaning, material removal, and surface modification. The intrinsic shortcomings of such an application are the need in the use of expensive and heavy pumping facilities and, what are more important, peculiarities of the waterjet-substrate interaction which limit material deformation by the incoming jet. These shortcomings are eliminated if the workpiece is impacted by the array of the water slugs, generated by the direct injection of high-intensity energy pulses into the water vessel (barrel) and ejection the portion of the water via the nozzle attached into the barrel. Such a device (barrel-nozzle combination) will constitute an effective and versatile manufacturing tool. Understanding of the phenomena that occur in the course of the energy injection into the water is necessary for the design of the desired device. The phenomena in question are determined by the ratio between the speed of the water in the barrel in the course of the energy injection and the speed of the shock waves in the water. If this ratio is much less than unity, the exit velocity is determined by the ratio between the cross section areas of the nozzle exit and the barrel. If the ratio in question approaches the unity, the water velocity at the nozzle exit is determined by the impact pressure. The device utilizing this principle is termed the water extruder. If however, the ratio is much more than unity the exit water velocity is determined by the superposition of shock waves developed in the fluid. This device termed the water cannon is able to accelerate the water slug to the speed far exceeding 1,000 m/sec. The numerical and experimental studies of water extruder were carried out. The numerical models were constructed and the variation of the water velocity and the water pressure in the barrel were investigated. Experimental setup for the study of the water extruder was constructed by the modification of Remington power tool. The experiments involved the piercing of metal strips. The effect of operational conditions on the maximal depth of the piecing was determined. Another series of experiments involved the study of the slug impact on plastic (lead) and brittle (concrete) materials. The effect of the stand off distance on the removal of both kinds of material was investigated. As the result the suggestions about the way of construction of the water extruders and their practical applications were made.

Commentary by Dr. Valentin Fuster
2002;():573-578. doi:10.1115/IMECE2002-33784.

Shape rolling of seamless rings constitutes an efficient manufacturing process offering excellent material yield, energy conservation, and component production, which require a minimum of subsequent machining operations. An increasing number of rings are being produced from high temperature Titanium and Nickel based super alloy materials for gas turbine engine parts such as vane and fan casings, exhaust casings, turbine shrouds, and combustion liners. With the increasing cost of super alloy raw materials and growing demand for cost-competitive parts, the importance of ring rolling to contoured shape becomes an increasingly important factor. This paper describes a new process modeling technique based on Upper Bound Elemental Technique (UBET) for shape rolling of super alloys. This tool provides a new design paradigm for an industry relying to heavily on designer experience and cut-and-try methods. As a rapid software tool to aid designers in developing ring-rolling process schedules thereby helping in reducing the design and analysis cycle time, the potential to capture the unique 3-D flow situation experienced in shape rolling of seamless rings is being explored. Numerical results have been compared with data available for high temperature alloys such as IN718 and Ti-6Al-4V.

Commentary by Dr. Valentin Fuster
2002;():579-583. doi:10.1115/IMECE2002-33785.

In this paper, the discrete element method is employed to simulate the powder compaction process and to produce the detailed results of micro mechanical response in particle scale. The DEM program is capable to calculate the contact between particles considering of surface adhesion, The statistical average properties of the compacts are then obtained from the sum of the particle movements and contacts. The calculated results show that the variation of the particle properties such as contact friction and elastic-plastic contact criteria can significantly affect the bulk response of the assembly. The connection between micro properties of particles and macroscopic continuum description of the behaviour of granular media is then discussed.

Commentary by Dr. Valentin Fuster
2002;():587-593. doi:10.1115/IMECE2002-32246.

A new indirect method to measure fraction solid on molten metals is presented. The method is based on the phenomena that when a metal sample (solid or liquid) rotates in a magnetic field (or the magnetic field rotates around a stationary sample), circulating eddy currents are induced in the sample, which generate an opposing torque proportional to amount of solid phase that precipitates in a solidifying melt between the liquidus and solidus temperatures. A new technique is applied for measuring fraction solid on commercial A319 aluminum alloy. The solidification curves obtained by the proposed method at different cooling rates are in a good agreement with the predictions made by the Scheil model.

Commentary by Dr. Valentin Fuster
2002;():595-600. doi:10.1115/IMECE2002-33790.

Water ice powder constitutes a potentially important manufacturing tool. Availability and cleanliness of this powder constitute its major advantage. It was shown that the ice particles can be used as an abrasive in the course of waterjet machining. Although the erosion potential of ice particle is inferior to that of the conventional abrasives the environmental soundness of ice enables us to expend the use of the ice abrasive jets on food industry, medicine, precision machining, etc. The principal issue in the use of the ice abrasives is particles formation. Analysis of various technologies showed that the most effective avenue in particles production is integration of the water freezing and ice decomposition. As the results, the desired flow rate of ice particles at the desired temperature and size distribution can be generated. The objective of the presented paper was the experimental investigation of the production of ice particles. An experimental set up was constructed and used for particles fabrication at controlled conditions. The acquired information was applied for the analysis of the phenomena leading to the particles formation. As the result a hypothetical mechanism of the ice decomposition was suggested and validated. The experiments involving the decontamination of the electronic devices, semiconductors, fabric, leather, food products, polished metal, soft plastics, rusted auto parts, etc were carried out in order to demonstrate the potential application of the ice blasting.

Topics: Ice
Commentary by Dr. Valentin Fuster
2002;():601-608. doi:10.1115/IMECE2002-33796.

Pastes occur as intermediates or final product forms in many industrially important manufacturing sectors. The use of computer simulation techniques, such as the finite element method, is becoming more common in the design of paste processing operations. A major problem in the application of this approach is the development of sufficiently representative materials models. It has been established that pastes may be described as elasto-viscoplastic materials with the plastic flow being governed by the Herschel-Bulkley relationship. This paper describes the development of analytical and numerical models that can be used as a basis for deriving the material parameters from experimental data obtained using extrusion, compression and bending procedures. Measurements have also been carried out on a model paste and the derived material parameters are compared with published data for the same paste. The merits of the three experimental methods are compared on this basis.

Commentary by Dr. Valentin Fuster
2002;():609-618. doi:10.1115/IMECE2002-33819.

The traveling solvent method (TSM) is a relatively new and promising technique for the production of high quality semiconductors. TSM has been tested on many alloys producing pure and homogeneous crystals. In the present study the effect of buoyancy convection on the growth of the Si0.15 Ge0.85 crystal grown by the traveling solvent method is investigated under different heating conditions. The full Navier-Stokes equations together with the energy and solutal equations were solved numerically using the finite element technique. The model take into consideration the losses of heat by radiation and the use of the phase diagram to determine the silicon concentration at the growth interface. Results revealed a strong convection in the solvent, which in turn is detrimental to the growth uniformity in the crystal rod. Additional numerical results showed that the convective heat transfer significantly influences the solute distribution in the liquid zone and the growth rate increases substantially.

Commentary by Dr. Valentin Fuster
2002;():621-628. doi:10.1115/IMECE2002-33113.

Point-particle Eulerian-Lagrangian DNS/LES simulations allow us to deal with a large number of small particles, using relatively modest computer resources. When doing LES, one can consider the subgrid particle-fluid coupling, using a subgrid model, or simply ignore it. We present a criterion to evaluate the importance of the subgrid particle-fluid coupling on: (i) the particle motion, and (ii) the resolved fluid-motion. The criterion assumes that the particles can be treated as point-particles, from the perspective of both the resolved and subgrid motions, and it is based on simple “local equilibrium” models for the interaction between the particles and the subgrid fluid-motion. The criterion was applied to a high-resolution channel flow LES, with a moderate particle-loading. The results indicate that: (i) for heavy particles, the common practice of ignoring the subgrid particle-fluid coupling is adequate, (ii) for very-light particles a model for the subgrid-driven particle-velocity fluctuations might be important.

Commentary by Dr. Valentin Fuster
2002;():629-634. doi:10.1115/IMECE2002-33114.

This paper deals with an Eulerian-Lagrangian model for dispersed multiphase flow in which all the interactions of any kind are taking into account. The fluid phase and particles interactions are two way coupled while all the collisions between the particles or between the particles and the walls are calculated. The Navier-Stokes equations (fluid phase continuity and momentum equations including exchange from the particle to the fluid is modeled to simulate the effect of the presence of the particles in the fluid phase) are solved on a staggered Eulerian grid by a finite volume discretisation type method. The originality of the Lagrangian approach used here for the particles motion, lies in the way of managing the collisions which are calculated using simple mechanical models such as a spring, dashpot and friction slider at the contact points following the Distinct Element Method DEM [1]. In the Lagrangian stage, motion’s calculation of each discrete particle including collisions effects is generally time consuming. In the context of this paper we shall show how to optimized the contacts tracking algorithm in an efficient way to increase significantly the capability of the DEM.

Commentary by Dr. Valentin Fuster
2002;():635-644. doi:10.1115/IMECE2002-33115.

A unique, super spatio-temporal resolution Digital Particle Image Velocimetry (DPIV) system for the analysis of time-dependent multiphase flows has been developed. The system delivers a sampling frequency between 1KHz and 10KHz, with continuous total acquisition time up to 4 secs and resolution 1Kx1K pixels down to 256×256 pixels. The hardware is integrated with sophisticated image processing algorithms that allow direct image segmentation in order to resolve the multiple phases present in the flow and provides quantitative information about the shape and size of droplets or bubbles present. Finally, the in-plane velocities are measured by a super-resolution, dynamically-adaptive cross-correlation algorithm which is coupled with a particle-tracking scheme. Each individual phase present in the flow is resolved with mean spatial resolution in the order of 3–4 pixels, and accuracy in the order of 0.01–0.1 pixels, while the spatial averaging effects of cross correlation are eliminated.

Commentary by Dr. Valentin Fuster
2002;():645-651. doi:10.1115/IMECE2002-33116.

A type of coal ash particles, fragments of sintered fly ash masses, can travel with flow in the furnace and settle on key places such as catalyst surfaces. Computational fluid dynamics (CFD) models are often used in the design process to prevent the carry over and settling of these particles at key locations. Particle size, density and drag coefficient are the most important hydrodynamic parameters involved in CFD modeling. The objective of this study was to experimentally determine particle size, shape, apparent density, and drag characteristics for sintered fly ash particles from a power plant. Particle size and shape were characterized by digital photography in three orthogonal directions and computer image analysis. Particle apparent density was also determined by volume and mass measurements. Particle terminal velocities in three directions were measured in water and each particle was also weighed in air and in water. The experimental data was analyzed and a method was developed to calculate particle equivalent diameter, equivalent ellipsoid size, apparent density, and drag coefficient distributions. Discussions were focused on developing a practical method that can characterize the aerodynamic properties of porous, sometimes skeletal particles.

Commentary by Dr. Valentin Fuster
2002;():655-661. doi:10.1115/IMECE2002-39345.

In addition to the governing equations, a properly posed mathematical problem requires a statement of the solution bounds and boundary conditions. Numerical methods applied to solve the governing equations must also implement proper solution bounds and boundary conditions. In developing a finite-volume, time-domain solver for electromagnetic computations, the author implemented a variety of approximate boundary conditions formulated to mimic reflecting metallic boundaries and truncated solution-domain (outer) boundaries. These approximate boundary conditions are presented and discussed in context of selected results for predicting the radar-cross section of various shapes (with analytic solutions available for comparison).

Commentary by Dr. Valentin Fuster
2002;():663-671. doi:10.1115/IMECE2002-39349.

Numerical modeling of the Pulsed Inductive Thruster exercising the magnetohydrodynamic code, MACH2 aims to provide bilateral validation of the thruster’s measured performance and the code’s capability of capturing the pertinent physical processes. Computed impulse values demonstrate excellent correlation to the experimental data for a range of energy levels and helium propellant-mass values. The effects of the vacuum tank wall and mass-injection scheme were investigated to show trivial changes in the overall performance.

Commentary by Dr. Valentin Fuster
2002;():673-681. doi:10.1115/IMECE2002-39352.

The present work develops a finite element discretized one-dimensional formulation for plasma-sheath dynamics, using multi-fluid equations. The applications include dc and rf sheath inside a glow discharge tube and a partially ionized plasma sheath inside a electric propulsion thruster channel. Based on the experimental data for multiple ionization of a noble gas, a third order polynomial has been used as a fit to describe ionization processes. Such a polynomial has been used to self-consistently calculate the rate of ionization in the plasma dynamic equations. The electron and ion number densities of the numerical solution decrease in the plasma-sheath region as expected. The ion velocity, sheath potential and electron temperature profiles also exhibit the expected behavior. The computed sheath potential compares well with the available experimental data. The model needs to be generalized in the near future for potential application to the high-speed air vehicles.

Commentary by Dr. Valentin Fuster
2002;():683-693. doi:10.1115/IMECE2002-39354.

High power electromagnetic plasma thrusters are being developed as primary in-space propulsion systems for future robotic and piloted space missions. Electromagnetic thrusters effectively process megawatts of electrical power, providing a wide range of specific impulse values to meet a variety of in-space propulsion requirements. Potential applications for high power thrusters include the orbit raising and maneuvering of large space platforms, lunar and planetary cargo transport, piloted planetary missions, asteroid rendezvous and sample return, and robotic deep space exploration. The NASA Glenn Research Center is developing MW-class magnetoplasmady-namic (MPD) thrusters and pulsed inductive thrusters (PIT) to support these diverse mission requirements. This paper provides an overview of the current GRC research program, describes the operating principles, challenges, and status of each technology, and outlines plans for further development.

Commentary by Dr. Valentin Fuster
2002;():697-703. doi:10.1115/IMECE2002-32346.

This work continues the studies of Moinuddin et al. [1], where experiments were performed on a streamwise external corner. The streamwise development of turbulent boundary layer over an external corner (chine) is influenced by secondary flow which is driven three-dimensionally. The direct effect of this secondary flow is to increase the drag force. Here secondary flow, which is known as Prandtl’s second kind, is induced by inequality of Reynolds stresses around the corner. This flow is expected to exhibit symmetry about the corner bisector. Moinuddin et al. [2,3] have established the symmetry of this flow based upon mean flow measurements. Normal wire measurements for the streamwise turbulence intensity profiles u′2 + , measured at about Reθ 5700 and 4.7 m from the model leading edge, are presented in this paper. Mean flow measurements show excellent agreement between Pitot tube and normal wire measurements. Comparisons are made for u′2 + , profiles at equal spanwise distance, from the corner, on both surfaces. The profiles agree quite well having nominal deviation depending on spanwise and normal distance from the corner. Isointensity contours also depict symmetrical turbulence distribution. It is also revealed that far from the corner, turbulence profiles agree well with the standard two-dimensional turbulence profile. The measurements agrees with the general behaviour expected from this kind of flow as reported by Xu & Pollard [4] from their LES calculation of flow in an annular square duct.

Commentary by Dr. Valentin Fuster
2002;():705-713. doi:10.1115/IMECE2002-32347.

The effect of several drag reducing devices on the near wake of a generic ground vehicle body was investigated. Drag and base pressure measurements were conducted to identify the effects of the devices on the base drag. A Particle Image Velocimetry (PIV) study was conducted to determine changes of the near wake flow field. Averages of more than 200 PIV velocity vector fields were used to compute the mean velocity and turbulent stresses at several cross section planes. The results of the drag and base pressure measurements show that significant reductions of the total aerodynamic drag (as high as 48%) can be achieved with relatively simple devices. The results also indicated that models with base cavity have lower drag than their counter parts without it. The base pressure distributions showed a strong effect of the ground, resulting in decrease of pressure towards the lower half of the base. The PIV study showed that the extent of the recirculation region is not strongly affected by the drag reducing devices. The tested devices however, were found to have a strong effect on the underbody flow. A rapid upward deflection of the underbody flow in the near wake was observed. The devices were also found to reduce the turbulent stresses in the near wake. The turbulent stresses were found to decrease in magnitude with increasing drag reduction.

Topics: Wakes
Commentary by Dr. Valentin Fuster
2002;():715-723. doi:10.1115/IMECE2002-32348.

A new pumping technology has been developed and patented by the Alberta Research Council [1–3] to address the problem of liquid loading in natural gas wells at low, depleted pressures. This technology consists of a pump installed at the bottom of the well bore that is driven by the reservoir gas pressure to bring the produced liquids to the surface as they accumulate thereby improving gas production from shallow gas wells. The above pump concept has been investigated in two stages of research. In the first stage, a mathematical model was developed to estimate the minimum reservoir pressure required to prevent liquid build up in a gas well with either: • the reservoir pressure (and flow) itself carrying the produced liquids to the surface in a two-phase flow, or • the reservoir gas pressure powering a pumping device to carry the produced liquids to the surface in the most efficient manner possible. The objective of the second stage of this investigation was to look at the feasibility of using a reciprocating pump powered by gas pressure. In particular, the effect of the pump Area Ratio (ratio of the area being pushed by the gas to the area pushing the liquid) on the use of reservoir gas pressure was investigated. There are approximately 70,000 flowing gas wells in Western Canada and these gas wells were categorized by depth and production rate. From this list of gas wells, a typical well was chosen and its production data and well characteristics were incorporated into the mathematical model. The model was tested in both the above-mentioned investigations and the results show that there is a significant increase in the operating range when the reservoir pressure is used more efficiently to produce gas from the well. It was determined that higher pump area ratios lead to a more efficient use of reservoir pressure and for the gas well investigated in this study, an optimum area ratio of 40 was identified as the best design. The concept of multistage pumping was also investigated. The results presented are the basis for experiments presently being designed that will validate the current model of the system and allow for possible improvements.

Commentary by Dr. Valentin Fuster
2002;():725-733. doi:10.1115/IMECE2002-32349.

A computational modeling method using the CFD codes GAMBIT and FLUENT jointly has been developed for analyzing the three-dimensional aerodynamic behavior of surface dimpled golf balls. Drag and lift coefficient values and fluid field solutions have been obtained for the balls with three different types of dimple pattern distributions, which consist of the dimples with the same or different pocket sizes and depths. The baseline case golf ball carries 422 circular dimples with the dimple distribution pattern very similar to that of a Spalding TOP-FLITE PLUS II ball. The computed drag and lift coefficients of this baseline ball stationary or spinning have been made to compare with some published wind-tunnel experimental results, and the agreement was found to be good. This indicates that the modeling method developed is relevant and suitable for predicting the ball flight behavior for varying dimple geometry and dimple pattern distribution designs. From this, the necessary ball surface design parameter changes can be found either to enhance or to limit the ball’s aerodynamic performance, which controls and determines the ball flying distance and trajectory accuracy after initial impact.

Commentary by Dr. Valentin Fuster
2002;():735-740. doi:10.1115/IMECE2002-32350.

A depth-averaged equation set is solved to simulate Mobile Bay circulation. A semi-implicit algorithm with an alternating-direction-implicit technique is employed to perform numerical computations on a staggered Cartesian grid mesh that covers the Mobile Bay area. The simulation results include effects from the four major rivers around Mobile Bay. Flow patterns and elevation contours are shown during flood and ebb tides. Velocity vectors and particle tracers are used to indicate the flow patterns and related transport of Mobile Bay circulation.

Commentary by Dr. Valentin Fuster
2002;():741-747. doi:10.1115/IMECE2002-32351.

The flow of Newtonian fluid (eg. water) in the test channel with an obstruction at the entrance placed in a wider channel was seen to be stagnant, forward or reverse depending on the position of the obstruction. This interesting flow phenomenon has potential benefit and can be employed in the control of energy and various flows in process engineering. This study was extended to non-Newtonian fluid for further investigation using flat plate as an obstruction. A low concentration polyacrylamide fluid solution (0.018%) showing non-Newtonian fluid behavior was used in this investigation. The parameters that affect the flow inside and around the test channel were the gap (g) between the obstruction geometry and the test channel, the Reynolds number and the length of the test channel. The maximum reverse flow inside the test channel observed was 20%–25% of the outside test channel velocity at g/w (gap to width) ratio of 1 for Reynolds number of 1000 to 3500. The results of the influence of the test channel length and the Reynolds number on the velocity ratio (Vi/Vo: inside velocity/outside velocity in the test channel) is also presented and discussed.

Commentary by Dr. Valentin Fuster
2002;():749-756. doi:10.1115/IMECE2002-32352.

A novel viscosity measurement technique was developed in which angular deflection-oscillation of a sealed quartz ampoule containing a semiconductor melt is measured upon application of a rotating magnetic field. This paper provides a theoretical basis for this novel method. Equations for coupled fluid flow and ampoule torsional oscillation were solved numerically. The predictions of the melt flow and ampoule oscillation were in good agreement with the experimental data. The results also showed that both electrical conductivity and viscosity could be calculated from the experimental data by a numerical fitting procedure. The transient velocity of the melt caused by the rotating magnetic field was found to reach steady state in about one minute, within which both the electrical conductivity and the viscosity of the melt can be obtained. This is a significant improvement over the existing oscillation cup method, which requires about one hour of measurement to obtain viscosity.

Commentary by Dr. Valentin Fuster
2002;():757-763. doi:10.1115/IMECE2002-33791.

It is known that local skin friction can be reduced by injecting microbubbles into a trubulent boundary layer. However, so far the mechanism of the reduction has never been understood. In the present study, the objective is to understand the characteristics of a turbulent flow field containing microbubbles with an experimental approach in order that the mechanism for the skin friction reduction is clearly elucidated. In order to measure the flow with the microbubbles, a combination of PIV and LIF methods is developed. Measurements are carried out for a horizontal channel flow with microbubbles by which the skin friction is reduced. Modifications of the wall turbulence due to the injection of the microbubbles are discussed.

Commentary by Dr. Valentin Fuster
2002;():765-772. doi:10.1115/IMECE2002-39157.

A steady state simulation for the flow past a circular cylinder at the sub-critical Reynolds number of 3900 is conducted using a variety of non-linear eddy viscosity-based two-equation κ-ε models. Although, this simulation compromises the transient characteristics of the flow, the solution obtained using a steady state simulation showed qualitative relevance. Steady state results were closely comparable to the far more expensive and supposedly more correct time-averaged solutions obtained using transient simulations. The dissipative effect due to such turbulence modeling by far overweighs the effect of the numerical dissipation. Such dissipation dampened the intrinsic self-excited unsteadiness known to exist in such flow and enabled steady state-like solution. In-house developed finite volume based code along with a commercial finite-element code, were used. Qualitative agreement is attainable for the surface-pressure distribution over the cylinder and the centerline streamwise velocity in the wake regions. For this type of problems, the time-averaged solutions obtained using transient simulation that employs the non-linear eddy viscosity-based two-equation κ-ε type models, offered marginal improvement over those obtained using steady state simulations.

Commentary by Dr. Valentin Fuster

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