bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of Single-Mode Richtmyer-Meshkov Instability
Authors: Mueschke Nicholas , Kraft Wayne N. , Dibua Odion , Andrews Malcolm J. , Jacobs Jeffrey W.
Published: October 2008

The Richtmyer-Meshkov (RM) instability occurs when a shock passes through a perturbed interface separating fluids of different densities. Similarly, RM instabilities may also occur when a perturbed interface between two incompressible fluids of different density is impulsively accelerated. We report work that investigates RM instabilities between incompressible media by way of numerical simulations that are matched to experiments reported by Niederhaus & Jacobs [1]. We also describe a compact, fractional time-step, two-dimensional, finite-volume numerical algorithm that solves the non-Bousinesq Euler equations explicitly on a Cartesian, co-located grid. Numerical advection of volume fractions and momentum is second-order accurate in space and unphysical oscillations are prevented by using Van Leer flux limiters [2,3]. An initial velocity impulse has been used to model the impulsive acceleration history found in the experiments [1]. We report accurate simulation of the experimentally measured early-, intermediate-, and late-time penetrations of one fluid into another.
Simulation of Natural Convection in a Differentially Heated Cavity
Authors: Aybar Hikmet S. , Kayaci Savas
Published: October 2008

Buoyancy-driven flow in a cavity can be observed in many application of thermal engineering, such as nuclear reactor insulation, ventilation of rooms, solar energy absorber, crystal growth, cooling of electronics chips, and cooling of steel or iron bars. Buoyancy-driven flow in a cavity has been studied using different solution methods. Validity of these numerical studies is performed by well-known benchmark problems. Differentially heated square cavity is one of the most widely used benchmark problems in convection-diffusion problems. In this study, the differentially heated cavity problem is modeled using control-volume method using different solution algorithms (QUICK and Upwind). The case matrix is formed (i.e. for different Ra number and for different mesh sizes) for this problem and the results are compared with the available solutions found in literature. The CPU time for the computations for the different cases with different solution algorithms are also given.
Numerical Prediction of Unsteady Flows Through Turbine Stator-Rotor Channels With Condensation
Authors: Sasao Yasuhiro , Yamamoto Satoru
Published: October 2008

Unsteady transonic flows with condensation through steam turbine stator-rotor channels are numerically predicted by using the numerical method developed by our group. Fundamental equations solved here consist of conservation laws of mixed gas, water vapor, water liquid, and the number density of water droplets, coupled with the momentum equations and the energy equation. Also the shear-stress transport (SST) turbulence model is employed to predict the turbulent quantities. The numerical method is based on the high-order high-resolution finite-difference method. The fourth-order monotone upstream-centered schemes for conservation laws (MUSCL) with the total variation diminishing (TVD) scheme, Roe’s approximate Riemann solver, and the lower-upper symmetric Gauss-Seidel (LU-SGS) scheme are employed in the numerical method. As numerical examples, transonic condensate flows of moist air through a turbine and a compressor cascade channel are first calculated. Also wet-steam turbine stator-rotor cascade channels are calculated assuming homogeneous and heterogeneous condensations.
Simulation of the Onset of Gas Entrainment From a CANDU Reactor Channel Under LOCA Conditions: II
Authors: Ahmad T. , Hassan I.
Published: October 2008

An experimental investigation has been carried out to simulate the onset of gas entrainment phenomenon from a stratified region through branches located on a semi-circular wall configuration, in close dimensional resemblance with a CANDU header-feeder system. New experimental data for the onset of gas entrainment was developed during single and multiple discharge from an air/water stratified region over a wide range of Froude numbers (0 to 100), in order to thoroughly understand the onset of gas entrainment phenomenon. The present data is necessary in validating the analytical and numerical models of the onset of gas entrainment, particularly at low Froude numbers. Part I of this paper, Andaleeb et al. (2005), provides the theoretical investigation of the single discharge case.
Unsteady Rotor-Stator Interaction in an Axial Flow Blower: Part I — Numerical and Experimental Flow Field Characterization
Authors: Ferna´ndez Oro J. M. , Argu¨elles Di´az K. M. , Santolaria Morros C. , Blanco Marigorta E.
Published: October 2008

The present study focuses on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single stage turbomachine. The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow blower of high reaction degree, relating them to working point variations and axial gap modifications. A numerical 3D simulation of the complete stage is carried out, using a commercial code that resolves the URANS set of equations. For the modeling of turbulence, a LES scheme is used in order to achieve a good description of the largest eddy structures of the flow. In the other hand, an experimental facility was developed to get a physical description of the flow inside the machine. Both static and dynamic measurements were used in order to describe the interaction phenomena. A directional probe with pressure transducers was employed for the static characterization, and hot wire anemometry techniques were used for the instantaneous response of the interaction. The scope is based on the development of a methodology to understand the flow mechanisms related to the blade passing frequency in a single rotor-stator interaction.
An Inverse-Design Method for Centrifugal Pump Impellers
Authors: Westra R. W. , Kruyt N. P. , Hoeijmakers H. W. M.
Published: October 2008

The development of an inverse-design method for the impellers of centrifugal pumps is presented. The flow inside the impeller channel is assumed to be irrotational, inviscid and incompressible. With the inverse-design method infinitely-thin impeller blades can be designed for a given meridional geometry and design conditions. The main design parameter is the mean-swirl distribution, which is specified from leading edge to trailing edge and from hub to shroud. The flow in the impeller channel is solved using the Finite Element Method, employing the mean-swirl distribution as a boundary condition. The blade shape is changed iteratively until the blade impenetrability condition is fulfilled. The method has been verified by considering a case for which an analytical solution is available and by reconstruction of an existing geometry, with known characteristics, using the inverse-design method. As an application of the method a mixed-flow impeller has been designed and the effect of changing the mean-swirl distribution on the resulting blade shape is clearly demonstrated.
An Investigation of Crossing Trajectory Effects in Turbulent Shear Flow (Keynote)
Authors: Thomas Lionel , Oesterle´ Benoiˆt
Published: October 2008

The dispersion of small inertial particles moving in a homogeneous, hypothetically stationary, shear flow is investigated using both theoretical analysis and numerical simulation, under one-way coupling approximation. In the theoretical approach, the previous studies are extended to the case of homogeneous shear flow with a corresponding anisotropic spectrum. As it is impossible to obtain a closed theoretical solution without some drastic simplifications, the motion of dispersed particles is also investigated using kinematic simulation where random Fourier modes are generated according to a prescribed anisotropic spectrum with a superimposed linear mean fluid velocity profile. The combined effects of particle Stokes number and dimensionless drift velocity (magnitude and direction) are investigated by computing the statistics from Lagrangian tracking of a large number of particles in many flow field realizations, and comparison is made between the observed effects in shear flow and in isotropic turbulence.
Synergistic Effects of Self-Recovering Viscoelastic Tribological Nanosystems
Authors: Bakhtiyarov Sayavur I.
Published: October 2008

This paper analyzes the possible mechanisms responsible for the synergistic performances of micellar copper oxide and polymer additives on wear and friction characteristics in tribological systems. In order to evaluate the synergistic effect, a new wear-friction test apparatus was developed and used in the presented work. The sensor electronic system was designed and built for simultaneous measurements of the temperature in the lubricating zone and the normal force. These two parameters allowed estimating a healing efficiency of the viscoelastic nanolubricant. The effect of both rheological properties (both viscous and elastic properties) and the composition (concentration of nanoparticles to base liquid and a surfactant) of the metalworking nanofluids on the tribological process performances was determined.
Measurements of Rotating Stall Inside a Centrifugal Pump Impeller
Authors: Johnson D. A. , Pedersen N. , Jacobsen C. B.
Published: October 2008

Velocity measurements have been obtained in a centrifugal pump with a volute. The measurements have been obtained between the blade passages of a shrouded impeller and in the volute region using laser Doppler velocimetry (LDV). Complimentary measurements have been obtained with pressure transducers circumferentially mounted on the volute. The flow through the impeller is measured at both design load and at several off-design conditions including severe off-design conditions. Results show that flow behaviour at design conditions Qd is well behaved. At reduced flow off-design conditions (0.25Qd) the measured flow pattern was altered significantly showing alternating stable stationary stalled and unstalled passages. Spectral analysis of the data from the LDV probe and the pressure probes showed a marked change in the spectrum as the stall phenomena occurs. This result is in contrast with previous researchers who have reported partially stalled flow passages or rotating stall conditions where the stall pattern rotated relative to the impeller with a regular frequency.
Unsteady Flow Field and Noise Generation in a Centrifugal Pump Impeller With a Vaneless Diffuser
Authors: Pavesi Giorgio , Ardizzon Guido , Cavazzini Giovanna
Published: October 2008

To improve understanding of the phenomena of stall in centrifugal pumps, extensive research was conducted to investigate the impact on flow field instabilities and the noise generated in a pump equipped with a diffuser. A pump fitted with a vaneless diffuser and a return channel was used as the test model. Flow velocity was measured at the pump and at diffuser inflow to establish a link between the flow field structure and acoustic radiation. Activity was based upon the cross spectral analysis of output signals from piezoelectric transducers placed flush with the wall at the inflow and outflow of the pump, and 3D fully-viscous unsteady computations. Results showed the jet-wake flow pattern induced an unstable vortex, which influenced flow discharging from the adjacent passage and destabilised jet-wake flow in the passage. Consequently, periodic fluctuations were seen at impeller discharge which were found to be coherent from blade to blade and possessed a rich harmonic content. With the exception of the total pressure in the far field, the pressure frequency scattering by the pump was found to be consistent when compared to the experimental and analytic results.
A Novel Vibrating Ribbon Technique
Authors: Watmuff Jonathan H.
Published: October 2008

A novel vibrating ribbon apparatus is described that is active over the full span of a wind tunnel test section. The spanwise uniformity of the vibration amplitude and other ribbon characteristics are considered in detail. The height of each end of the ribbon above the test plate can be adjusted in situ, while the ribbon is vibrating and with flow in the test section, thereby allowing the response of the layer to be easily tuned. The growth of the wave amplitude downstream of the ribbon is shown to agree with numerical predictions. However, two or three wavelengths of development are required before the wave amplitude follows the predicted growth. The flow around an inactive ribbon is examined using a commercial CFD solver and features such as a miniature separation bubble just downstream of the ribbon are revealed. The distance required for the mean flow to recover from the disturbance introduced by the ribbon is greater when the ribbon is located further from the wall. The mean flow recovers to form a boundary layer that is slightly thicker than the undisturbed flow. Experimental measurements indicate that the distance required for the wave motions to follow predicted behavior is about 4 or 5 times larger than distance for recovery of the mean flow.
Transport in Mesoscale Cooling Systems
Authors: Garimella Suresh V.
Published: October 2008

The growing trend towards miniaturization and increasing functionality of microelectronics systems has driven the search for novel microfluidic technologies for cooling, which span a range of length and time scales. Fluid and heat transport associated with single- and two-phase microchannel transport and micropumping, as well as miniature piezoelectric fans for fluidic actuation, is discussed and fundamental issues in understanding these cooling approaches identified.
3D Viscous Inverse Design of Vaned Diffuser to Suppress Flow Unsteadiness in a Centrifugal Compressor
Authors: Mileshin Victor I. , Brailko Igor A. , Startsev Andrew N. , Orekhov Igor K.
Published: October 2008

Present paper is devoted to numerical investigation of unsteadiness caused by impeller-diffuser interaction in a 8:1 total pressure ratio centrifugal compressor. The compressor designed by CIAM [7], and manufactured and tested by Customer gave satisfactory performances even under the first test. Further development requires new insights and advanced numerical tools. In this context, this paper presents Navier-Stokes computations of 3D viscous unsteady flow field within the impeller-diffuser configuration. Steady and unsteady computations indicated spacious zone of low velocity / reverse flow on pressure surface of the diffuser vane. To suppress this reverse flow, new vaned diffuser has been tailored through application of 3D inverse design procedure for Navier-Stokes equations [8]. Subsequent steady and unsteady N-S calculations performed for compressor with the new diffuser demonstrated depression of reverse flow within diffuser and different unsteady loading of the diffuser vane.
Experimental Research on a Pump Suction Sump With Improved Structure
Authors: Fan Yi , Liu Shuhong , Wu Yulin , Li Yong , Xu Zhaofeng
Published: October 2008

Pump suction sump is an important part of pump station and its flow situations influence the performance of pumping system greatly. In this paper, the pump suction sump with particular structure is designed to improve the flow situations near the pump intake. In order to validate the effect of the improved structure, three experiments were carried out on both the original and improved structures, including the experiment of critical flow rate for air entrainment, the experiment of free water surface height measurement, and 3D PIV experiments at the pump sump. The results of the experiments show that water depth and inlet flow velocity influence the flow situations greatly. The results also show that the improved structure is useful to improve flow situations in pump suction sump.
Simulation of Flow Inside an Axial-Flow Pump With Adjustable Guide Vanes
Authors: Kochevsky Alexey N. , Kozlov Stanislav N. , Aye Khin Maung , Schelyaev Alexander Y. , Konshin Vladimir N.
Published: October 2008

The article describes numerical research of fluid flow inside an axial-flow pump that includes adjustable guide vanes, impeller and discharge channel. The guide vanes in the extreme position cut off the flow through the pump. The article presents the performance curves of the pump at different pitch angle of those guide vanes, as well as some corresponding flow patterns. Cavitation characteristics are also presented. The results were obtained using the CFD software tools CFX-BladeGenPlus, CFX-TASCflow and CFX-5. In the previous article, the authors have presented a comprehensive comparison of numerical results with available experimental results for a similar pump. As it was demonstrated, the performance curves of the pump depend strongly on the guide vanes pitch angle. Conclusions concerning these dependencies are drawn. A particular attention is paid for evaluation of performance of the pump with swirl flow downstream of it.
Computational Study of Pressure Pulsation in a Medium Specific Speed Pump
Authors: Timouchev Serguei
Published: October 2008

The centrifugal pump of high specific speed with a diagonal type of impeller flow is studied experimentally and numerically. Both 2D and 3D numerical methods are used by applying acoustics–vortex equations. Increasing energetic parameters of centrifugal pumps requires a more complex geometry of the impeller and volute as one needs to raise the specific speed of the pump to provide a higher efficiency value. The pump of higher specific speed has an impeller with curved blades and diagonal meridional section. The flow outgoing the impeller has an essential axial component of velocity. Thus the two dimensional approach will not give the accurate prediction of pressure pulsations in the volute casing. This is why the new 3-dimensional method has been elaborated for this task. The 3D computational results of pressure pulsations are compared with those obtained by 2D-computation Measurements show that in the beginning of volute, in the pseudo-sound zone, amplitude of Blade Passing Frequency (BPF) spectral component is higher than that at the pump outlet by an order of magnitude. The 3-Dimensional analysis gives a good agreement with experimental data while the 2D prediction underestimates the BPF amplitude in the beginning of volute.
Flow Structures and Frictional Characteristics on Two-Phase Flow in Microchannels in PEM Fuel Cells
Authors: Lee Eon Soo , Hidrovo Carlos H. , Steinbrenner Julie E. , Wang Fu-Min , Vigneron Sebastien , Goodson Kenneth E. , Eaton John K.
Published: October 2008

This experimental paper presents a study of gas-liquid two phase flow in rectangular channels of 500μm × 45μm and 23.7mm long with different wall conditions of hydrophilic and hydrophobic surface, in order to investigate the flow structures and the corresponding friction factors of simulated microchannels of PEMFC. The main flow in the channel is air and liquid water is injected at a single or several discrete locations in one side wall of the channel. The flow structure of liquid water in hydrophilic wall conditioned channel starts from wavy flow, develops to stable stratified film flow, and then transits to unstable fluctuating film flow, as the pressure drop and the flow velocity of air increase from around 10 kPa to over 100 kPa. The flow structure in hydrophobic channel develops from the slug flow to slug-and-film flow with increasing pressure drop and flow velocity. The pressure drop for single phase flow is measured for a base line study, and the fRe product is in close agreement with the theoretical value (fRe = 85) of the conventional laminar flow of aspect ratio 1:11. At the low range of water injection rate, the gas phase fRe product of the two phase flow based on the whole channel area was not substantially affected by the water introduction. However, as the water injection rate increases up to 100 μL/min, the gas phase fRe product based on the whole channel area deviates highly from the single phase theoretical value. The gas phase fRe product with the actual gas phase area corrected by the liquid phase film thickness agrees with the single phase theoretical value.
Suppression of Cavitation Instabilities by Jet Injection at Inducer Inlet
Authors: Fujii Akira , Mizuno Shinichi , Horiguchi Hironori , Tsujimoto Yoshinobu
Published: October 2008

Cavitation instabilities such as rotating cavitation and cavitation surge often occur in turbopump inducers for rocket engine. In the present study, a method for suppressing the cavitation instabilities in an inducer by jet injection is examined. Through eight nozzles placed at the upstream of the inducer, jets were injected in circumferential direction. The axial position of nozzles, speed of jet flow and direction of jet injection were changed. Through the experiments under various conditions, it was found that the occurrence regions of cavitation instabilities are decreased significantly with the injection in the same direction as shaft rotation with the jet flow rate about 10% of total flow. The flow field was also examined to clarify the mechanism for the suppression by injection. It was found that the incidence angle and cavity length were reduced by the injection, which decreases the occurrence region of instabilities.
Backflow From Inducer and Its Dynamics
Authors: Tsujimoto Yoshinobu , Horiguchi Hironori , Qiao Xiangyu
Published: October 2008

The present paper summarizes recent studies on the dynamics of backflow vortex structure associated with cavitation instabilities in turbopump inducers. First, the cause of cavitation instabilities is discussed. Various methods for the suppression of cavitation instabilities are then reviewed to illustrate the importance of backflow vortex cavitation on instabilities. The characteristics of backflow vortices are described based on experimental observations. Calculations based on the k-ε turbulence model are used for clarifying the mechanisms of inlet backflow and its response to flow rate fluctuations. Backflow vortex structure is simulated by LES calculations on a simplified geometry. Cavity volume is estimated from the volume of the regions with the pressure lower than the vapour pressure and its response to flow rate fluctuation is clarified. From the results obtained, the effects of backflow vortex cavitation on cavitation instabilities are discussed.
High Temperature Overhung Pumps: Cooling Optimization
Authors: Cipolla M.
Published: October 2008

A typical industrial application of high temperature pumps involves handling of fluids up to 400 °C. This is critical for pump bearing housing, where thermal dissipation is not effective due to geometric configuration. Therefore, without any external cooling system, bearings and lubricating oil temperatures can exceed allowable values prescribed by both API 610 Reference Standard [1] and bearing manufacturer [2]. Particularly, for a overhung pump, when pumped fluid temperature is above 200 °C, external cooling system is necessary and water is usually used for this purpose. Consequently, water availability must be taken into account when considering pump’s location, which is particularly difficult in desert areas. From these considerations was the idea to enhance the heat transfer of the pump support, in order to avoid any need of cooling water. The problem has been dealt with numerical analysis and experimental tests. First, we have considered the original support in the most critical situation, the stand-by condition, where no forced convection (fan) is effective. From the results pertaining to currently used support, we have got the hints to improve heat transfer by a full redesign. Finally an experimental validation has been set up. The measures gained allow us to validate hypothesis taken into consideration in the numerical simulation.
Direct Numerical Simulation of Turbulent Flow and Mass Transfer Around a Rotating Circular Cylinder
Authors: Hwang Jong-Yeon , Yang Kyung-Soo , Bremhorst Klaus
Published: October 2008

Characteristics of turbulent flow and mass transfer around a rotating circular cylinder are investigated by Direct Numerical Simulation. Mass-transfer results are presented at a high Schmidt number (Sc = 1670). The concentration field is computed for three different cases of low Reynolds number, Re*R = 161, 348 and 623, based on the cylinder radius and friction velocity. Results confirm that the thickness of Nernst diffusion layer is very small compared with that of viscous sub-layer in the case of high Sc mass transfer. A strong correlation of the concentration field with streamwise and vertical velocity components is noticed. However, that is not the case with the spanwise velocity component. Visualization of instantaneous concentration reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. The correlation between Sherwood number and Reynolds number is consistent with other experiments currently available.
Multi-Path Gas Ultrasonic Flow Meter Performance at Low Velocity
Authors: Morrow Thomas B.
Published: October 2008

Multi-path gas ultrasonic flow meters are used to measure the flow rate of natural gas in custody-transfer metering applications. Steady-flow tests were performed in the high-pressure loop (HPL) of the Southwest Research Institute (SwRI) Metering Research Facility (MRF) flowing natural gas through two 300 mm (12-inch) diameter multi-path ultrasonic flow meters with different ultrasonic path configurations. Tests were performed with both small and large temperature differences between the flowing gas temperature and the outdoor ambient temperature. This paper presents the results of the large temperature difference tests with and without an upstream flow conditioner for one multi-path ultrasonic meter in the low-flow range of 0.15 m/s (0.5 ft/s) to 0.30 m/s (1 ft/s). Test conditions were selected to complement a computational fluid dynamics (CFD) study performed by Morrison and Brar [2004,2005] at Texas A&M University. The experimental results confirm that the gas flow in the ultrasonic meter was thermally stratified (as predicted by Morrison and Brar [2004]) and show the effects of thermal stratification on path velocities, meter diagnostic path velocity ratios, and on meter accuracy. The results show that the flow conditioner was relatively ineffective in smoothing the axial velocity profile distortion caused by thermal stratification in this low velocity range.
Cavitation in MicroElectroMechanical Systems (MEMS): Importance, Deviations From Conventional Scale, and Preliminary Results
Authors: Peles Yoav , Mishra Chandan
Published: October 2008

Hydrodynamic cavitation in micro systems is a fundamental engineering problem that is poorly understood. The lack of knowledge on cavitation relevant to MEMS devices is impeding the practical realization of novel high-velocity microfluidic machines. This paper divulges differences between cavitation occurring inside micro and conventional systems, and also indicates the limited applicability of conventional knowledge to predict and understand cavitating flows in micro-domains. A detailed discussion delineating the possible reasons of such a divergence is presented in this article. Additionally, selected results obtained from preliminary experiments on cavitation in micro-domains are presented.
Hydrodynamic Cavitation in Flow Through Micro-Constriction Elements Entrenched in Rectangular Microchannels
Authors: Mishra Chandan , Peles Yoav
Published: October 2008

Hydrodynamic cavitation, the explosive growth and catastrophic collapse of vapor bubbles, has immense impact on the design and performance of hydraulic machinery in the macro world. However, cavitation in high-speed microfluidic systems has received scarce attention and hardly been reported. This article reports the presence of hydrodynamic cavitation in the flow of de-ionized water through 11.5–40micron wide rectangular slot micro-orifices entrenched inside 100–200micron wide microchannels. Pioneering experimental investigations on hydrodynamic cavitation in rudimentary microfluidic configurations such as slot micro-orifices has been presented and unique cavitating flow patterns have been identified. Assorted cavitating (two-phase) flow patterns including incipient, choking and supercavitation have been detected. Designers of high-velocity microfluidic systems, especially Power-MEMS devices, need to be aware of the deleterious effects of cavitation as it can significantly affect device performance. The effects of micro-orifice and microchannel size on cavitation have been discussed and results indicate the existence of strong scale effects. Incipient and choking cavitation numbers are observed to increase with increasing micro-orifice size, while the orifice discharge coefficient plummets once cavitation activity erupts. In addition, inlet pressure effects on several cavitation parameters have been discussed and compared with established macro-scale results. The cavitating flow patterns encountered are significantly influenced by the micro-orifice and microchannel size. Flow rate choking occurs irrespective of the inlet pressures and is a direct consequence of cavitation inside the micro-orifice. Cavitation hysteresis is observed but its effects are more marked for the smallest micro-orifice.
Diesel Droplet Diffusion in Isotropic Turbulence With Digital Holographic Cinematography
Authors: Gopalan Balaji , Malkiel Edwin , Sheng Jian , Katz Joseph
Published: October 2008

High-speed in-line digital holographic cinematography was used to investigate the diffusion of droplets in locally isotropic turbulence. Droplets of diesel fuel (0.3–0.9mm diameter, specific gravity of 0.85) were injected into a 37×37×37mm3 sample volume located in the center of a 160-liter tank. The turbulence was generated by 4 spinning grids, located symmetrically in the corners of the tank, and was characterized prior to the experiments. The sample volume was back illuminated with two perpendicular collimated beams of coherent laser light and time series of in-line holograms were recorded with two high-speed digital cameras at 500 frames/sec. Numerical reconstruction generated a time series of high-resolution images of the droplets throughout the sample volume. We developed an algorithm for automatically detecting the droplet trajectories from each view, for matching the two views to obtain the three-dimensional tracks, and for calculating the time history of velocity. We also measured the mean fluid motion using 2-D PIV. The data enabled us to calculate the Lagrangian velocity autocorrelation function.
An Investigation on Energy Transfer Mechanism Caused in Rotating Flow Passage of Turbomachinery: New Concept of Physical Parameters in Rectangular Coordinate System
Authors: Tanaka Takaharu
Published: October 2008

All the physical parameters, such as energy, force, velocity, and acceleration are constructed from two different kinds; one is real and the other is imaginary. Their acting directions are normal to each other. The former acts horizontal direction and causes visible kinetic movement on fluid particle. All the supplied energy is utilized and consumed. The latter acts vertical direction but does not cause any visible kinetic movement on fluid particle. All the energy transfer from mechanical to hydraulic and from hydraulic to mechanical is caused by the imaginary parameters in vertical direction.
Thermodynamic Effect on a Cavitating Inducer in Liquid Nitrogen
Authors: Yoshida Yoshiki , Kikuta Kengo , Hasegawa Satoshi , Shimagaki Mitsuru , Nakamura Noriaki , Tokumasu Takashi
Published: October 2008

For experimental investigations of the thermodynamic effect on a cavitating inducer, it is nesessary to observe the cavitation. However, visualizations of the cavitation are not so easy in cryogenic flow. For this reason, we estimated the cavity region in liquid nitrogen based on measurements of the pressure fluctuation near the blade tip. In the present study, we focused on the length of the tip cavitation as a cavitation parameter. Comparison of the tip cavity length in liquid nitrogen (80 K) with that in cold water (296 K) allowed us to estimate the strength of the thermodynamic effect. The degree of thermodynamic effect was found to increase with an increase of the cavity length. The estimated temperature depression caused by vaporization increased rapidly when the cavity length extended over the throat. In addition, the estimated temperature inside the bubble nearly reached the temperature of the triple point when the pump performance deteriorated.
Reduction of the Aerodynamic Tonal Noise of a Forward-Curved Centrifugal Fan by Modification of the Volute Tongue Geometry
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Santolaria-Morros Carlos , Pereiras-Garci´a Bruno
Published: October 2008

In this work, an experimental study about the influence of some geometric features on the aeroacoustic behavior of a squirrel-cage fan, used in automotive air conditioning units, has been carried out. The study focused on the effect of both the shape and the position of the volute tongue on the noise generated by the fan. Different geometric configurations were tested in order to compare the results. First of all, the performance curves were measured in a standardized test facility. Then, the acoustic behavior of the fan was characterized by means of acoustic pressure measurements near the fan inlet. The comparison of the test results indicated a great dependence of both the shape and the position of the volute tongue and the noise generation. In particular, some geometric configurations of the volute tongue were able to reduce the fan noise generation without reducing the fan performance.
Observations Regarding the Nature of Oil-Water Phase Inversion and Instability in Laminar Flow Through Circular Tubes Containing Static Mixers
Authors: Sood Arun , Cheluget Eric , Karnik Umesh
Published: October 2008

Liquid-liquid emulsions will undergo a phase inversion, in which the dispersed phase becomes the continuous phase and vice versa, under certain conditions. A phase inversion is not a smooth transition and an emulsion close to the inversion point may oscillate back and forth between the oil-in-water (O/W) and water-in-oil (W/O) forms, creating flow instabilities that may be detrimental in certain industrial situations. The results of laboratory laminar flow experiments in which an aqueous and an organic liquid phase are emulsified as they flow through a circular tube containing a commercial high-shear static mixer are discussed. As the concentration of the dispersed phase and/or its flow rate is increased, flow instabilities are initiated in the test-section and are measured as fluctuations in pressure drop. The intensity of these fluctuations reaches a maximum as the liquid-liquid system approaches the phase inversion point. Once a stable phase inversion is achieved, the fluctuations subside. This phenomenon was observed over a wide range of viscosity ratios for the two liquid phases, but was absent for low viscosity ratios and low-shear static mixers.
Large Eddy Simulation (LES) and Time-Resolved Particle Image Velocimetry (TR-PIV) in the Wake of a Cavitating Hydrofoil
Authors: Wosnik Martin , Qin Qiao , Kawakami Damien T. , Arndt Roger E. A.
Published: October 2008

A Large Eddy Simulation (LES) approach for cavitating flow, based on a virtual single-phase, fully compressible cavitation model which includes the effects of incondensable gas, has been shown to be capable of capturing the complex dynamical features of highly unsteady cavitating flows of two-dimensional hydrofoils. Here the LES results are compared to Time-Resolved Particle Image Velocimetry (TR-PIV) in the wake of a cavitating NACA 0015 hydrofoil, with particular attention to the predicted vortex shedding mechanisms. Despite some difficulty with obtaining vector fields from vortical clouds of vaporous-gaseous bubbles with cross-correlation techniques, the initial results seem promising in that they confirm the existence of a primary vortex pair (type A-B). In addition to TR-PIV, the cavitation cloud shedding was also documented with phase-locked, time-resolved photography and high speed volume-illuminated video, both with simultaneous imaging of side and plan views of the foil. All three experimental techniques confirm the need for fully three-dimensional simulations to properly describe the unsteady, three-dimensional cavitation cloud shedding mechanism.
Scaling of Favorable Pressure Gradient Turbulent Boundary Layers With Eventual Relaminarization
Authors: Cal Rau´l Bayoa´n , Wang Xia , Castillo Luciano
Published: October 2008

Applying similarity analysis to the RANS equations of motion for a pressure gradient turbulent boundary layer, Castillo and George [1] obtained the scalings for the mean deficit velocity and the Reynolds stresses. Following this analysis, Castillo and George studied favorable pressure gradient (FPG) turbulent boundary layers. They were able to obtain a single curve for FPG flows when scaling the mean deficit velocity profiles. In this study, FPG turbulent boundary layers are analyzed as well as relaminarized boundary layers subjected to an even stronger FPG. It is found that the mean deficit velocity profiles diminish when scaled using the Castillo and George [1] scaling, U∞, and the Zagarola and Smits [2] scaling, U∞δ*/δ. In addition, Reynolds stress data has been analyzed and it is found that the relaminarized boundary layer data decreases drastically in all components of the Reynolds stresses. Furthermore, it will be shown that the shape of the profile for the wall-normal and Reynolds shear stress components change drastically given the relaminarized state. Therefore, the mean velocity deficit profiles as well as Reynolds stresses are found to be necessary in order to understand not only FPG flows, but also relaminarized boundary layers.
Direct Preparation of Ce0.8Sm0.2O1.9 Powders Oxidized With H2O2 for Low Temperature SOFCs Application
Authors: Huang Jianbing , Mao Zongqiang , Zhu Bin , Yang Lizhai , Peng Ranran , Gao Ruifeng
Published: October 2008

A novel method was developed to prepare fine doped ceria (DCO) powders directly. Ceria doped with 20 mol. % of samarium (Ce0.8Sm0.2O1.9, SDC) was prepared by in-situ oxidization of hydroxide precipitates with H2O2 in the solutions. The resultant powder desiccated at 85°C overnight was characterized by X-ray diffraction (XRD), thermogravimetry /differential thermal analysis (TG/DTA), and transmission electron microscopy (TEM). The XRD pattern showed that the as-dried SDC powder is single phase with a cubic fluorite structure like that of pure CeO2. An anode-supported SOFC was also fabricated based on SDC and 20wt. % (62mol. %Li2CO3–38 mol. %K2CO3) composite electrolyte, LiNiO2 as cathode and NiO as anode, by cold pressing. Using hydrogen as the fuel and air as the oxidant, the I-V and I-P characteristics exhibit excellent performances and the maximum power densities are about 696, 469, 377 and 240 mWcm−2 at 650, 600, 550 and 500°C, respectively.
Effect of Various Electrolyte Compositions on the NiO Degradation in Molten Carbonates
Authors: Scaccia Silvera , Frangini Stefano
Published: October 2008

In the present paper we report the NiO solubility in a variety of alkali carbonate compositions in presence of MgO, CaCO3, BaCO3 and La2O3 additions under different conditions of gas composition and temperature. Two types of binary eutectic melts were chosen, namely the standard electrolyte (62–38) (Li-K)2CO3 and (52–48) % (Li-Na)2CO3 mixtures. The ternary eutectic melt chosen was (43.5-31.5-25.0) mol % (Li-Na-K)2CO3. The observed reduction of NiO solubility induced by the additives can be explained in terms of a higher basic character of all the modified electrolytes, although the NiO dissolution still follows an acidic dissolution mechanism in all the conditions under study.
The Nature of Flooding and Drying in Polymer Electrolyte Fuel Cells
Authors: Chuang P. A. , Turhan A. , Heller A. K. , Brenizer J. S. , Trabold T. A. , Mench M. M.
Published: October 2008

Two different 50 cm2 fuel cells operated at high current density (1.3A/cm2–1.5A/cm2) were visualized using neutron imaging, and the liquid water content in the flow channels and diffusion media under the lands and channels was calculated and compared. At high current density with fully humidified inlet flow, a direct comparison between flooded and non-flooded conditions was achieved by increasing the fuel cell temperature over a small range, until voltage loss from flooding was alleviated. Results indicate that a surprisingly small mass of liquid water is responsible for a significant voltage loss. The deleterious effects of flooding are therefore more easily explained with a locally segregated flooded pore model, rather than a homogeneously flooded pore and blockage phenomenon. Anode dryout was similarly observed and quantified, and results indicate that an exceedingly small mass of water is responsible for significant voltage loss, which is consistent with expectations. The results presented help to form a more complete vision of the flooding loss and anode dryout phenomena in PEFCs.
Analysis on the Performance Characteristics of SOFC/GT Hybrid Systems Based on a Commercially Available MW-Class Gas Turbine
Authors: Song Tae Won , Sohn Jeong L. , Kim Tong Seop , Ro Sung Tack
Published: October 2008

To investigate the possible applications of the SOFC/MGT hybrid system to large electric power generations, a study for the kW-class hybrid power system conducted in our group is extended to the MW-class hybrid system in this study. Because of the matured technology of the gas turbine and commercial availability in the market, it is reasonable to construct a hybrid system with the selection of a gas turbine as an off-the-shelf item. For this purpose, the performance analysis is conducted to find out the optimal power size of the hybrid system based on a commercially available gas turbine. The optimal power size has to be selected by considering specifications of a selected gas turbine which limit the performance of the hybrid system. Also, the cell temperature of the SOFC is another limiting parameter to be considered in the selection of the optimal power size. Because of different system configuration of the hybrid system, the control strategies for the part-load operation of the MW-class hybrid system are quite different from the kW-class case. Also, it is necessary to consider that the control of supplied air to the MW-class gas turbine is typically done by the variable inlet guide vane located in front of the compressor inlet, instead of the control of variable rotational speed of the kW-class micro gas turbine. Performance characteristics at part-load operating conditions with different kinds of control strategies of supplied fuel and air to the hybrid system are investigated in this study.
Parameters Affecting the Performance of a Residential-Scale Stationary Fuel Cell System
Authors: Davis Mark W. , Fanney A. Hunter , LaBarre Michael J. , Henderson Kenneth R. , Dougherty Brian P.
Published: October 2008

Researchers at the National Institute of Standards and Technology (NIST) have measured the performance of a residential fuel cell system when subjected to various environmental and load conditions. The system, which uses natural gas as its source fuel, is capable of generating electrical power at three nominal power levels (2.5 kW, 4.0 kW, and 5.0 kW) while providing thermal energy for user-supplied loads. Testing was conducted to determine the influence of ambient temperature, relative humidity, electrical load, and thermal load on system performance. Steady-state and transient tests were conducted. The steady-state tests were performed in accordance with the American Society of Mechanical Engineering (ASME) Fuel Cell Power Systems Performance Test Code (PTC-50) for fuel cell power systems. The results of the investigation are being used to develop a proposed rating procedure for residential fuel cell units.
Stresses in Proton Exchange Membranes Due to Hydration-Dehydration Cycles
Authors: Tang Yaliang , Santare Michael H. , Karlsson Anette M. , Cleghorn Simon , Johnson William B.
Published: October 2008

Durability of the proton exchange membranes (PEM) is a major technical barrier to the economic viability of stationary and transportation applications of PEM fuel cells. In order to reach Department of Energy objectives for automotive PEM fuel cells, a design lifetime of 5,000 hours over a wide temperature range is required. Reaching these lifetimes is an extremely challenging technical problem. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. The lifetime is limited due to gradual degradation of both the electro-chemical and hygro-thermo-mechanical properties of the membranes. Eventually the system fails due to a critical reduction of the voltage or mechanical damage. However, the hygro-thermo-mechanical loading of the membranes and how this effects the lifetime of the fuel cell is not understood. The long-term objective of the research is to establish a fundamental understanding of the mechanical processes in degradation and how they influence the lifetime of PEMs. In this paper, we discuss the finite element models developed to investigate the in-situ stresses in polymer membranes.
Analysis of a Gas Turbine Almost Real Open Cycle Linked to the SOFC Module Behaviour
Authors: Lo Mastro Fabio , La Marca Giuseppe , Blando Gandolfo
Published: October 2008

Solid oxide fuel cells (SOFCs) are particular promising electrochemical generators for their high operating temperature that makes them suitable for integration with gas turbine cycles and cogeneration. The kind of fuel cell taken into account is the tubular SOFC technology, mainly developed by Siemens-Westinghouse. The SOFC module is fed with natural gas with internal reforming and internal air preheating. Elevated pressures are adopted in order to increase both fuel cell efficiency and power density. The inlet air temperature is set to 630 °C, and the inlet fuel temperature to 200 °C. The heat generated by irreversibility at the electrodes structure is given to the fuel and air flow, and partially lost by the module external carter. A significant fraction of the heat is used by the endothermic reforming reactions, thus reducing the requested cooling air flow and enhancing the fuel heating value. The SOFC module finally generates a single outlet stream: both cathode and anode flue gases (depleted air and depleted fuel) react burning in a combustion chamber. Sometimes it is possible flue gases to preheat the inlet air flow and afterwards to expand in a gas turbine driving the turboblower. The authors consider the matching between the SOFC module and a system consisting of two coaxial turbomachines, i.e. a turbine and a turboblower. They analyse a turboblower flowed by air led into the SOFC at 630 °C and separately a gas turbine driving the turboblower, but flowed by a different fluid consisting of SOFC exhausted gases. For sake of simplicity, despite the high turbine inlet temperature (TIT), they assume there is not cooling of the blades. In order to increase the efficiency of the whole system they have studied the variation of the main parameters of the two turbomachines, especially the compression ratio and they have found that only a correct employment of flue gases enthalpy can achieve a good efficiency of the power plant. Furthermore they have used NIST-JANAF coefficients to describe the polytropic processes both of the compression and of the expansion.
In Plane Permeability Measurements for Gas Diffusion Layers
Authors: Feser J. P. , Prasad A. K. , Advani S.
Published: October 2008

A radial flow device was fabricated to experimentally characterize the in-plane flow behavior of gas diffusion layers (GDL). Radial flow of gas and liquid through the GDL result in the same permeability values. Finally, four types of commercially available GDL are characterized at various levels of compression.