bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Rotor-Stator Interaction in an Axial Flow Blower: Part II — Deterministic Stresses Analysis
Authors: Ferna´ndez Oro J. M. , Argu¨elles Di´az K. M. , Santolaria Morros C. , Blanco Marigorta E.
Published: October 2008

Since the instantaneous phase-averaged flow field has been characterized and properly described through both numerical and experimental studies in a single stage axial flow blower, the next step is to identify the sources of unsteadiness related to blade passing frequencies. The construction of the deterministic stress tensor in both rotating and fixed frames of reference, through a sequential averaging technique, is extremely useful for this purpose. This kind of tensor shows the location and intensity of the main interaction characteristics of the flow, allowing a perfect segregation of the effects of every blade row onto the total unsteady scenario of the complete stage. The steady signature of the stator wakes, still present at the exit plane, downstream the forward rotor, will be related to the residual deterministic kinetic energy of the mixed-out flow. The migration of these unsteady features onto the averaged flow field will be used to understand the recovery process that occurs when the flow passes through the rotor of the stage, linking flow physical phenomena with the transport and convection of the deterministic stresses.
Aspects of the Cavitating Propeller Tip Vortex as a Source of Inboard Noise and Vibration
Authors: van Wijngaarden Erik , Bosschers Johan , Kuiper Gert
Published: October 2008

This paper surveys fluid dynamic-acoustic mechanisms that may explain low-frequent, broadband hull excitation experienced on board of ships and caused by propeller cavitation. Observations obtained from sea trials and model scale experiments are used to describe the hydrodynamics involved in each particular mechanism. The investigations are still ongoing and aim to identify causes of broadband inboard noise and vibration on passenger vessels in the frequency range of 20 to 70 Hz.
Experimental Investigation of Interstitial Fluid Effects on Particle Fluctuating Motion
Authors: Hadinoto K. , Sinclair Curtis J.
Published: October 2008

The importance of interstitial fluid effects on particle fluctuating motion in gas-particle or liquid-particle flows with significant particle-particle collisions can be characterized by the ratio of the coefficient of restitution for inelastic particle-particle collisions in a fluid ef to the coefficient of restitution for collisions in a vacuum es. In previous research, the ratio ef/es has been found to depend on the impact Stokes number St, which relates the particle inertia to the viscous force. The value of the impact Stokes number is known to be a function of the particle velocity at impact, the size and density of the particle, and the fluid viscosity. In the present work, the effect of the interstitial fluid on particle fluctuating motion is investigated experimentally using LDV/PDPA in a vertical pipe flow configuration. The influence of the variation in the particle loading and Reynolds number, which affects the particle impact velocity and, hence, ef, is probed using particles of two different densities with comparable sizes. Specifically, the downward flow of 70 micron glass beads (density = 2500 kg/m3) and 60 micron hollow ceramic microspheres (density = 700 kg/m3) is investigated for solids loadings (ratio of solids mass flowrate to gas mass flowrate) from 0.4 to 7 and Reynolds numbers which vary from 6000 to 13,000. For this range of conditions, the values for ef range between 0.65 and 0.94 (0.94 is the value for es for glass beads colliding in a vacuum). Trends in the mean and fluctuating velocities for both the gas and particle phases, as well as the gas turbulence modulation in the presence of particles, are discussed in relation to the degree of influence of the interstitial fluid on the details of the particle motion.
Numerical Simulation of Acoustic Streaming in Gas-Liquid Two-Phase Flow
Authors: Lu Bo , Ruggles Arthur E.
Published: October 2008

Acoustic streaming phenomena pertaining to liquid-gas two-phase flow in a one-dimensional rigid duct is investigated numerically. The oscillatory bubbly flow is generated due to the sinusoidal vibration of the vertical left wall of the enclosure. Time-averaged streaming flow patterns exist in the duct as a consequence of interaction between gas bubbles and liquid which are similar to the Rayleigh-type acoustic streaming phenomena extensively investigated in single-phase flow. The liquid is treated as incompressible with a homogeneous distribution of non-condensable gas bubbles. The system is modeled with coupled nonlinear and flux-conservative partial differential equations combined with the Rayleigh-Plesset equation governing the bubble radius. The viscous interaction between bubbles and the surrounding incompressible liquid phase is the main mechanism for attenuation of the wave energy considered in this analysis. The numerical solutions are obtained by a control-volume based finite-volume Lagrangian method.
Prediction of the Noise From a Multi-Stage Centrifugal Pump
Authors: Kato Chisachi , Yoshimura Shinobu , Yamade Yoshinobu , Jiang Yu Yan , Wang Hong , Imai Ryuta , Katsura Hiroyuki , Yoshida Tetsuya , Takano Yashushi
Published: October 2008

Presented in this paper is a one-way coupled simulation of fluid flow and structural analyses that is applied to the prediction of the noise radiated from the external surface of a 5-stage centrifugal pump. A large eddy simulation is firstly applied to compute pressure fluctuation on the internal surface of the pump. These computed fluctuations are then fed to the structural analysis based on an explicit dynamic finite element method that computes the elastic wave propagating in the solid. The computed pressure fluctuations are compared with measurements in several points in the diffuser passage and a good agreement is obtained in terms of their frequency spectra. The vibration velocities on the external surface of the pump are also compared with the measured equivalents, which show a reasonably good agreement. The proposed method thus seems quite a promising tool for prediction of and reduction in the flow-induced noise generated from hydraulic turbomachinery in general.
A Computational and Experimental Analysis of the Flow Around a Tractor-Trailer
Authors: Mathur Gaurav S. , Taghavi Ray , Hale Richard , Bianchi Silvia , Myburgh Riaan
Published: October 2008

An unsteady computational fluid dynamics simulation of the viscous-turbulent flow around a tractor-trailer has been done using FLUENT’s realizable k-epsilon turbulence model and is supported by experimental validation. The primary objective was to compute a time-dependent solution of the flow around a tractor-trailer in a virtual wind tunnel and study the pressures on the floor.
The Aerodynamics of Three-Dimensional Vaned Diffusers in Industrial Centrifugal Compressors
Authors: Abdelwahab Ahmed
Published: October 2008

Vaned diffusers have been used successfully as efficient and compact dynamic pressure recovery devices in industrial centrifugal compressor stages. Typically such diffusers consist of a cascade of two-dimensional blades distributed circumferentially at close proximity to the impeller exit. In this paper three low-solidity diffuser blade geometries are numerically investigated. The first geometry employs variable stagger stacking of similar blade sections along the blade span. The second employs linearly inclined stacking to generate blade lean along the diffuser span. The third geometry employs the conventional two-dimensional low-solidity diffuser geometry with no variable stagger or lean. The variable stagger blade arrangement has the potential of better aligning the diffuser leading edges with the highly non-uniform flow leaving the impeller. Both variable stagger and linearly leaned diffuser blade arrangements, however, have the effect of redistributing the blade loading and flow streamlines in the spanwise direction leading to improved efficiency and pressure recovery capacity of the diffuser. In this paper a description of the proposed diffuser geometries is presented. The results of Three-dimensional Navier-Stokes numerical simulations of the three centrifugal compressor arrangements are discussed. Comparisons between the performance of the two and three-dimensional diffuser blade geometries are presented. The comparisons indeed show that the variable stagger and leaned diffusers present an improvement in the diffuser operating range and pressure recovery capacity over the conventional two-dimensional diffuser geometry.
An Experimental Investigation of the Pressure-Velocity Cross-Correlation in an Axisymmetric Jet
Authors: Hall Andre´ M. , Glauser Mark N. , Tinney Charles E.
Published: October 2008

This study investigates the strength of the pressure-velocity correlations of a Mach 0.6, axisymmetric jet, with an exit nozzle diameter of 50.8mm. Experiments are conducted at a constant exit temperature of 25°C, and exit pressure and temperature are balanced with ambient conditions. The instantaneous velocity measurements are acquired using a multi-component LDA system who’s measurement volume is traversed along several radial and streamwise locations within the potential core, and mixing layer regions of the flow. The fluctuating lip pressure is simultaneously sampled by an azimuthal array of (15) dynamic transducers, evenly spaced at 24°. These are positioned just outside the shear layer near the jet exit at z/D = 0.875, and 1.75R from the centerline, where the pressure field has been shown to be hydrodynamic. From this multi-point evaluation, the cross-correlations between the near-field pressure array (fixed), and streamwise component of the velocity field (traversed) are examined as a function of radial, streamwise, and also azimuthal separation. The results illustrate a remarkable coherence between the near field pressure and the velocity field, on the order of 25%. Streamwise convection velocities of 0.77Uj and 0.73Uj are calculated within the potential core and shear layer, respectively. Analysis of the coherency spectra illustrates the frequency band of the correlations and suggest that the potential core and mixing layer regions of the flow are, in general, governed by the high and low frequency motions of the flow, respectively. The azimuthal modal distribution of the cross-correlation shows the dominance of the column mode of the jet, with no higher modes exhibited within the potential core region, and only modes 1 & 2 within the shear layer.
CFD Application for the Characterization of Surface Pressures on Telescopes
Authors: Kaushik Balaji , Hale Richard D. , Taghavi Ray
Published: October 2008

Aerodynamic trade studies in support of an interdisciplinary research program for large ground based telescopes are addressed. Numerous CFD (Computational Fluid Dynamics) trade studies were carried out to help identify the initial critical configuration of the telescope. The highest pressures induced on the reflective surface of the telescope mirror in the critical configuration were used in structural analysis. A module that correlated disparate discretizations in structural and fluid analyses through common parent geometry was developed. This module mapped surface pressures from the CFD discretization to the structural discretization using a weighted average technique. Experimental validation of the CFD results was carried out in the University of Kansas subsonic wind tunnel. The results from the CFD analysis and the wind tunnel experiments were in close agreement, with the maximum variation of pressures being 1%–8%. The preliminary telescope configuration that induced the highest pressure on the reflective surface of the primary mirror was identified as one inclined at 60° from the vertical plane and facing the wind directly. An “open-air” CFD model was developed that simulated the observatory shut-off operating conditions of 15 m/s wind speed and a fail-safe operating condition of 50 m/s wind speed. Critical local total gage pressures were 165 Pa and 1400 Pa at 15 and 50 m/s wind speeds respectively.
Method for Cavitation Erosion Prediction: Model Development
Authors: Dular Matevzˇ , Stoffel Bernd , Sˇirok Brane
Published: October 2008

A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A two-dimensional hydrofoil with circular leading edge was used for the experiments. In addition, the hydrofoil geometry was modified to obtain some three-dimensional cavitation effects. A thin copper foil, applied to the surface of the hydrofoil, was used as an erosion sensor. The cavitation phenomenon on hydrofoils at different flow conditions (system pressure, water gas content, flow velocity) was observed. Images of vapour cavities from above and from a side view were taken. Plausible results that showed a significant relationship between cavitation erosion and the visual effects of cavitation made it possible to use these information to develop a cavitation erosion model. The model is based on the physical description of different phenomena, which are involved in the process of pit formation — pressure wave emission and its attenuation, micro-jet formation, the jet impact to the solid surface and pit creation. The model is capable to predict the influence of significant parameters as flow velocity and gas content of water. The model that was developed on the basis of measurements of cavitation on a single hydrofoil was later tested on an actual hydraulic machine in the form of a radial pump. The predicted magnitude and distribution of cavitation damage relates well to the experimentally measured one.
ALE Calculations of Flow Through Rotary Positive Displacement Machines
Authors: Vande Voorde John B. , Vierendeels Jan
Published: October 2008

In a rotating positive-displacement compressor, such as a screw compressor, only a time dependent flow calculation is meaningful. The Arbitrary Lagrangean-Eulerean (ALE) formulation of the flow equations allows CFD with moving grids. Due to the complex movement of the rotors, a powerful grid manipulator is necessary. The algorithm presented in this paper moves the nodes of a block-structured grid based on the solution of a Laplace potential-equation ∇2φ = 0 in a two-dimensional section of the flow domain. The qualities of a Laplace solution for grid generation have been used in grid generators and manipulators since Winslow. The difference with this new algorithm is that now this solution is explicitly obtained on an unstructured grid to allow greater control over the movement of the grid. The grid manipulation algorithm is demonstrated on an oil-free screw compressor geometry. Results of this calculation confirm the applicability of this algorithm to such complex geometries.
Computational Study of Ejector-Pumps
Authors: Timouchev Serguei , Aksenov Andrey , Bogdanov Victor , Karpyshev Alexander
Published: October 2008

Computational results of 3D turbulent compressible gas flow in a single-nozzle ejector are compared with experimental data. Full Navier-Stokes equations and k-ε model of turbulence are used for mathematical model of gas flow. In computations the suction gas flow rate was determined and compared with experimental one. Two computational grids — coarse and fine are used to perform simulation. The fine grid is differ from coarse one by adaptation near the nozzle of active gas. Comparison of results carried out on coarse and fine grids shows that the accuracy of coarse grid is enough to get reliable results. Difference of computed and experimental results is less then 4% for the flow rate of passive gas. These results enable to make computational study of the multi-nozzle water-steam ejector. Condensation of steam is taken into account by introducing the equilibrium model of condensation. It is found that location of nozzles and its length are the important parameters of ejector influencing considerably its characteristics. The process of the condensation of water vapor significantly influences the work of ejector with an increase of the suction flow rate by a factor of 2.
Sequential Simulation Used in the Computer Aided Design of Airfoils for Horizontal Axis Wind Turbine Rotors
Authors: Al-Zubaidy Sarim N. , Johnson Alwyn , Bridge Jacqueline
Published: October 2008

In the past twenty years wind energy remerged on the world scene with a very healthy growth rate, it has outstripped photovoltaics as the world’s fastest growing energy source, with a growth rate in excess of 30 percent per annum. The proposed paper presents a numerical procedure for the analysis and design of Horizontal Axis Wind Turbine rotors for fabrication in countries with limited manufacturing base and limited design expertise. To ascertain the accuracy and to determine where further improvements could be initiated; numerical findings were then compared with published experimental test data, the compression showed an average deviation of less than 3%. Once the approach was validated and standardized an airfoil design was produced. A computational fluid dynamic code coupled with a simple numerical algorithm aided the inverse design procedure. The final design is well proportioned and theoretically able to meet the stated objective and satisfied the constraints. The generated geometrical data is in a form suitable for manufacture using local manufacturing capabilities, the primary objective of this work.
A Phase-Field Method for Interface-Tracking Simulation of Two-Phase Flows
Authors: Takada Naoki , Misawa Masaki , Tomiyama Akio
Published: October 2008

For interface-tracking simulation of two-phase flows, we propose a new computational method, NS-PFM, combining Navier-Stokes (NS) equations with phase-field model (PFM). Based on the free energy theory, PFM describes an interface as a volumetric zone across which physical properties vary continuously. Surface tension is defined as an excessive free energy per unit area induced by density gradient. Consequently, PFM simplifies the interface-tracking procedure by use of a standard technique. The proposed NS-PFM was applied to several problems of incompressible, isothermal two-phase flow with the same density ratio as that of an air-water system. In this method, the Cahn-Hilliard (CH) equation was used for predicting interface configuration. It was confirmed through numerical simulations that (1) the flux driven by chemical potential gradient in the CH equation plays an important role in interfacial advection and reconstruction, (2) the NS-PFM gives good predictions for pressure increase inside a bubble caused by the surface tension, (3) coalescence of liquid film and single drop falling through a stagnant gas was well simulated, and (4) collapse of liquid column under gravity was predicted in good agreement with other available data. Then, another version of NS-PFM was proposed and applied to a direct simulation of bubble nucleation of a non-ideal fluid in the vicinity of the critical point, which demonstrated the capability of NS-PFM to capture liquid-vapor interface motion in boiling and condensation.
Dynamic Vapour Fraction Measurement in Turbopump Inducers by X-Rays
Authors: Hassan Walid , Legoupil Samuel , Barre Stephane , Rebattet Claude
Published: October 2008

This work intended to evaluate the instantaneous vapour fraction in the turbo-pump inducer of a liquid propellant rocket engine. Experimentations held on an experimental pump test facility and cavitation was attained by reducing the inlet pressure in the machine while maintaining constant the inducer rotational speed. Measurements of vapour fraction through the rotating inducer were achieved by means of an x-ray-based system. The system exerted an industrial x-ray generator and 10 collimated scintillation detectors. Detectors were functioning in current mode thus permitting an acquisition at 5 kHz for each detector. A reference x-ray detector situated between the x-ray generator and the machine permitted the treatment of x-ray beam energy fluctuations related to industrial generators [1, 2, 3]. Acquisitions were performed in three axial positions on the inducer. For each measurement position, three cavitation sequences with different flow rate conditions (Q/Qn = 0.9, 1, 1.1, where Qn is the nominal flow rate) were accomplished. Each cycle is performed by decreasing gradually the pressure while maintaining an imposed rotational speed of 4000 rpm. Each test is constituted of 10 pressure points varying from 2.40 to 0.48 bars representing a complete cavitation sequence. X-ray acquisition was performed for each pressure point and it was carried out for 10 seconds thus corresponding to 667 tours of the inducer. Vapour fraction was determined instantaneously thus showing the applicability and the precision of the method in such measurements despite of the geometry and rotation speed constraints. Consequently a quantitative and qualitative evaluation of the vapour fraction is presented. Results show that the vapour distribution is well related to cavitation development on the blades of the inducer for steady cavitation condition.
Numerical Modeling of Flow Distribution in Microfluidics Systems
Authors: Majumdar Alok , Cole Helen , Chen C. P.
Published: October 2008

This paper describes an application of a general purpose computer program, GFSSP (Generalized Fluid System Simulation Program) for calculating flow distribution in a network of micro-channels. GFSSP employs a finite volume formulation of mass and momentum conservation equations in a network consisting of nodes and branches. Mass conservation equation is solved for pressures at the nodes while the momentum conservation equation is solved at the branches to calculate flowrate. The system of equations describing the fluid network is solved by a numerical method that is a combination of the Newton-Raphson and successive substitution methods. The numerical results have been compared with test data and detailed CFD (computational Fluid Dynamics) calculations. The agreement between test data and predictions is satisfactory. The discrepancies between the predictions and test data can be attributed to the frictional correlation which does not include the effect of surface tension or electro-kinetic effect.
Analyses Hydrodynamic Structure of Cross Water Jet and Its Performance of Soil Improvement
Authors: Shibazaki Mitsuhiro , Yoshida Hiroshi , Yoshida Kenji , Horii Kiyoshi , Kataoka Isao
Published: October 2008

Analyses of water jet based on two-fluid model of two-phase dispersed flow have been carried out for single water jet and cross water jet in relation to the water jet technology in civil engineering. Mass and momentum conservation equations for liquid phase (droplet) gas phase (air) were formulated separately (two-fluid model formulation). Physical modeling of diffusion of droplets, drag coefficient of droplet in dispersed flow, shear stress at jet interface, etc has been carried out in detail and constitutive equations for these physical phenomena have been developed. Based on the two-fluid model basic equations and constitutive equations, one-dimensional analysis has been carried out considering simplified mode and hydrodynamic structure of water jet was well predicted. In the practical application of present analyses, some preliminary analyses on cross jet where two water jets collide with certain collision angles have been carried out and the predicted results reasonably explain the experimental results.
DES, Hybrid RANS/LES and PANS Models for Unsteady Separated Turbulent Flow Simulations
Authors: Basu D. , Hamed A. , Das K.
Published: October 2008

This paper presents computational results for two DES (Detached Eddy Simulation), one hybrid RANS (Reynolds Averaged Navier-Stokes)/ LES (Large Eddy Simulation) and some preliminary results from PANS (Partially Averaged Navier-Stokes) turbulence for simulation of unsteady separated turbulent flows. The models are implemented in a full 3-D Navier Stokes solver and are based on the two-equation k-ε model. The formulations of each model are presented and results are analyzed for subsonic flow over a Backward Facing Step (BFS). Simulations are carried out using a 3rd order Roe scheme. A comparative assessment is made between the predictions from the DES, hybrid and PANS models. The predicted results are compared with the available experimental data for skin-friction coefficient, and different turbulent quantities. The three-dimensionality of the flow field and the separated fine scale structures are presented through the Q iso-surfaces.
Computational Simulation of Supersonic Flow Using Reynolds Stress Model
Authors: Abouali Omid , Ahmadi Goodarz , Rabiee Ataollah
Published: October 2008

The case of a supersonic turbulent flows with Mach number 2.5 and Reynolds number 1.23×106 based on the diameter of after body, around a body with incidence angles of 14° was studied. The nose length was 3 times the diameter with a third degree polynomial variation, and total length of the body was 13 diameters. Reynolds Averaged Navier-Stokes Equation was solved using central differencing scheme. The Reynolds Stress Model was used to account for the effect of turbulence on the flow field. The experimental data consist of surface pressure measurement at six axial locations. The pressure distributions were compared with the experimental data and the computer simulation results using Baldwin-Lumax and k-ε models. RSM results were found to show good agreement with the experimental data, while the Baldwin-Lumax model predictions deviated from the experimental data at the leeward on the after body because of a large cross-flow separation. The cross-sectional Mach number contours were also presented. It was shown that in addition to the outer shock, a cross-flow shock wave was also present in the flow region.
Oblique Shock Waves Interaction in a Non-Steady Three Dimensional Rotating Flow
Authors: Alhussan Khaled
Published: October 2008

This paper will explain the numerical analysis and the mapping of the flow in a confined region. In this paper some characteristics of non-steady, compressible, flow are explored, including compression and expansion wave interactions and creation. The results will show a promising achievement, first, to understand the flow structure inside a supersonic confined region, second, to use this knowledge to interpolate the numerical results in order to achieve a design methodology that will benefit the industrial applications for example in turbomachinery. Results including contour plots of static pressure, total pressure, Mach number, temperature and velocity vectors will show the structure of rotating oblique shock waves in a complex three-dimensional conical surface. A CFD analysis enables one to understand the complex flow structure inside this confined region. Through this computational analysis, a better interpretation of the physical phenomenon of the three dimensional rotting oblique shock waves can be achieved. It is essential to evaluate the ability of numerical technique that can solve problems in which compression and expansion waves occur. In particular it is necessary to understand the details of developing a mesh that will allow resolution of some discontinuities in similar flow.
Influence of Rotor Axial Thermal Growth on Rotordynamic Forces of High-Low Labyrinth Seals in Steam Turbines
Authors: Xi Jinxiang , Rhode David L.
Published: October 2008

Rotors in steam turbines experience significant axial shifting during start-up and shut-down process due to thermal expansion. This axial-shifting could significantly alter the flow pattern and the flow-induced rotordynamic forces in labyrinth seals, which in turn, can considerably affect the rotor-seal system’s performance. This paper investigates the influence of the rotor-axial-shifting on leakage rate and rotordynamic forces for high-low labyrinth seals under different geometrical and operational conditions. A well-established CFD-perturbation model was employed to predict the rotordynamic coefficients. A surprisingly large effect was found for rotordynamic characteristics due to changes in seal configurations caused by rotor axial shifting. It was also found that less destabilizing effect arose from rotor-axial-shifting in the leakage flow direction whereas a more destabilizing effect arose from shifting against the leakage flow direction. A tentative explanation was proposed for the large sensitivities of dynamic forces to the off-design operations with rotor-axial-shifting.
Predicting Turbine Performance of High Specific Speed Pumps Using CFD
Authors: White J. D. , Holloway A. G. L. , Gerber A. G.
Published: October 2008

A pump with a specific speed of 12000 was chosen to operate as a turbine (PAT) for a micro-hydro site having 5 m of head. Turbine performance of the pump was unavailable so it was simulated using CFD. The CFD model was first verified by comparison of simulated pump performance and manufacturer data. Simulated PAT performance covered a range of flow rates, from one to three times that of pump best efficiency point (BEP), for blade angles of 0 and ± 4°. The PAT BEP was located at a flow rate of 1.4 times that of pump BEP and a head of 1.6 times. For the specific site this corresponded to a shaft power of 32 k W and a flow rate of 770 1/s. The PAT was found to have an extended range of good efficiency, > 60%, for up to 3 times the pump BEP flow rate.
Wake Structure and Dynamic Thrust of an Unsteady Airfoil
Authors: Fuchiwaki Masaki , Tanaka Kazuhiro
Published: October 2008

The detailed wake structure behind pitching airfoil and heaving airfoil at a low Reynolds number region was measured by PIV. Moreover, dynamic thrust acting on them in water tunnel was measured by a six-axes sensor. At the high non-dimensional trailing edge velocity and the non-dimensional heaving velocity, the thrust producing vortex street is formed clearly. Moreover, it has been founded that not only the distance between vortices becomes narrow but also vorticity increases as the non-dimensional trailing edge velocity and the non-dimensional heaving velocity increase. The averaged dynamic thrust acting on a pitching airfoil and a heaving airfoil increases as the non-dimensional trailing edge velocity and the non-dimensional heaving velocity increase. The hysteresis loops of dynamic thrust acting on a pitching airfoil and a heaving airfoil show reentrant and convexity shapes characteristics. The dynamic behavior of dynamic thrust acting on a heaving airfoil is different from that on a pitching airfoil. The thrust efficiency of a pitching airfoil increased up to Vp = 0.7 rapidly and maximum thrust efficiency was 0.34. The thrust efficiency of a heaving airfoil increased up to Vp = 0.5 rapidly and the maximum thrust efficiency was 0.20.
Analysis of Two-Phase Supersonic Flow in Jet Pumps
Authors: Kandil S. M. , Lear W. E. , Sherif S. A.
Published: October 2008

A jet pump may be constructed from a pair of concentric tubes in which the center tube is shaped as a converging-diverging nozzle. Primary fluid is allowed to accelerate through the nozzle, thus creating a low-pressure region at the nozzle exit. Secondary fluid flowing in the peripheral region is drawn into the low-pressure region and is thus accelerated. In this study, the jet pump is employed as part of a space thermal-management system based on a cycle known as the Solar Integrated Thermal Management and Power (SITMAP). The latter is a combined vapor compression cycle and a Rankine cycle with the compression device being a jet pump instead of the regular compressor. The jet pump has several advantages for space applications as it involves no moving parts, a feature that results in decreasing the weight and vibration level while increasing the system reliability. The working fluid is cryogenic nitrogen, which is readily present onboard the spacecraft. This study presents a detailed component analysis of the jet pump allowing for two-phase supersonic flow. The model also accounts for Fabri choking either at the inlet or at an aerodynamic throat in the mixing chamber. The model also accounts for flow choking at the exit of the mixing chamber. The different choking situations limit the ability of the jet pump to entrain more secondary flow once the flow is choked at any location. In this study the various choking regimes will be identified and the entrainment ratios corresponding to the different choking scenarios will be calculated.
Cavitation Effects on Fluid Structure Interaction in the Case of a 2D Hydrofoil
Authors: Ausoni Philippe , Farhat Mohamed , Avellan Franc¸ois , Escaler Xavier , Egusquiza Eduard
Published: October 2008

In the present study, we have carried out an experimental investigation on the fluid-structure interaction caused by Karman vortices in the wake of a truncated 2D hydrofoil. The instrumentation involves a high frequency accelerometer and high speed visualisation. The mechanical response of the hydrofoil to the hydrodynamic excitation is monitored with the help of a portable digital vibrometer. Moreover, a specific optical device is developed to investigate the dynamic of the cavitating wake. The survey of the generation frequency of the Karman vortices with respect to the flow velocity reveals a Strouhal behaviour and three resonances of the hydrofoil. Out of hydro-elastic coupling conditions, the observation of the vortex structures reveals a strong 3D pattern despite the fact that the hydrofoil is 2D. The maximum fluid-structure interaction occurs for the torsional mode where lock-in is observed for upstream velocities ranging from 11 to 13 m/s. In this case, the vortices exhibit a 2D structure. The cavitation occurrence within the core of Karman vortices leads to a significant increase of their generation frequency. We have observed that hydrofoil resonance may be whether avoided or triggered by cavitation development. The study of the Karman vortices dynamic reveals that their advection velocity increases (4%) with the development of the wake cavitation meanwhile their streamwise spacing decreases.
Design and Optimization of an Industrial Pump: Application of Genetic Algorithms and Neural Network
Authors: Demeulenaere Alain , Purwanto Aji , Ligout Alban , Hirsch Charles , Dijkers Ronal , Visser Frank
Published: October 2008

This paper presents an integrated environment FINETM/Design3D developed for the optimization of turbomachinery blade shapes. The methodology relies on the interaction between a genetic algorithm, an artificial neural network, a database and user generated objective functions and constraints. The optimization is coupled to the FINETM/Turbo environment of NUMECA. The present paper focuses on the application of the multipoint optimization algorithm to the design of an industrial pump. The large range of mass flow over which the pump should operate motivates the use of multipoint optimization. The optimization exercise focuses on the efficiency, the head and the NPSH at two operating conditions characterized by largely different mass flows.
Evaluation of Ultrasonic Methods for In-Situ Real-Time Characterization of Drilling Mud
Authors: Bamberger Judith Ann , Greenwood Margaret S.
Published: October 2008

A real time multi-functional ultrasonic sensor system is proposed to provide automated drilling fluid monitoring that can improve the capability and development of slimhole and microhole drilling. This type of reliable, accurate, and affordable drilling fluid monitoring will reduce the overall costs in exploration and production. It will also allow more effective drilling process automation while providing rig personnel a safer and more efficient work environment. Accurate and timely measurements of drilling fluid properties such as flow rate, density, viscosity, and solid loading are key components for characterizing rate of drill penetration, providing early warning of lost circulation, and for use in real-time well control. Continuous drilling fluid monitoring enhances drilling economics by reducing the risk of costly drilling downtime, increasing production performance, and improving well control. Investigations conducted to characterize physical properties of drilling mud indicate that ultrasound can be used to provide real-time, in-situ process monitoring and control. Three types of ultrasonic measurements were evaluated which include analysis of in wall, through wall and direct contact signals. In wall measurements provide acoustic impedance (the slurry density and speed of sound product). Through wall and direct contact measurements provide speed of sound and attenuation. This information is combined to determine physical properties such as slurry density, solids concentration and can be used to detect particle size changes and the presence of low levels of gas. The measurements showed that for the frequency range investigated in-wall measurements were obtained over the slurry density range from 1500 to 2200 kg/m3 (10 to 17 pounds solids per gallon of drilling fluid). Other measurements were obtained at densities in the 1500 to 1800 kg/m3 range. These promising measurement results show that ultrasound can be used for real-time in-situ characterization of the drilling process by monitoring drilling mud characteristics.
Testing and Evaluation of Aluminum Coated Bipolar Plates of PEM Fuel Cells Operating at 70° C
Authors: Hung Yue , Tawfik Hazem
Published: October 2008

Corrosion resistant metal treated bipolar plates with higher rigidity and electrical conductivity than graphite were developed and tested for PEM fuel cell applications. Six replicas of single cells were fabricated; two of graphite composites bipolar plates and the other four plates were coated aluminum. Two different high corrosion resistant coatings were used in this study and were applied to each pair of the metallic plates. An E-TEK Series 14-W MEA with carbon cloth GDL, thickness of Nafion <50 microns, <1mg/cm^2 total platinum content (anode & cathode) and 6.45 cm2 active electrode areas, was fitted to each cell and operated under identical conditions. The obtained data from the two graphite cells were averaged and plotted and the other aluminum cells’ data were similarly treated and plotted on the same graph for comparison. Generally, the metallic treated bipolar plate provided at least a 22% savings in hydrogen consumption in comparison to graphite. This is attributed to the lower bulk and surface contact resistance of the coated aluminum plates used in this study in relation to graphite. The results of the lifetime testing conducted at temperature of 70° C under loading condition ranging from 0 to 0.6 W that showed no indication of power degradation due to metal corrosion for at least 60 hours.
Glucose Fueled Alkaline Fuel Cell
Authors: Schechner Pinchas , Bubis Eugenia , Mor Lea
Published: October 2008

The electrical behavior of a room temperature membraneless Alkaline Fuel Cell, with incorporated platinum particles in the anode and fueled with glucose, is reported. The Open Circuit Voltage, at different initial glucose concentrations was measured. Changes on the glucose concentration with time were monitored with the dinitrosalicylic acid method. Qualitative Thin Layer Chromatography demonstrates that the electrodes induce polymerization of the glucose. The electrical yield of the system was measured with different external resistors. The Open Circuit Voltage reaches a saturation value of 0.78±0.03 V at [glu]0 > 0.67 M. During four hours in Open Circuit conditions, there is a 20% drop in the concentration of reducing sugar in the fuel cell. Thin Layer Chromatography experiments show that the electrodes catalyze non-electrochemical glucose polymerization reactions. Assuming that the glucose is oxidized to gluconic acid, the electrical yield of the system is around 5%.
Analysis, Modeling, and Validation for the Thermal Dynamics of a Polymer Electrolyte Membrane Fuel Cell System
Authors: Mu¨ller Eric A. , Stefanopoulou Anna G.
Published: October 2008

A control-oriented mathematical model of a polymer electrolyte membrane (PEM) fuel cell stack is developed and experimentally verified. The model predicts the bulk fuel cell transient temperature and voltage as a function of the current drawn and the inlet coolant conditions. The model enables thermal control synthesis and optimization and can be used for estimating the system performance. Unlike other existing thermal models, it includes the gas supply system, which is assumed to be capable of controlling perfectly the excess air and hydrogen ratio. The fuel cell voltage is calculated quasi-statically. Measurement data of a 1.25 kW, 24-cell fuel cell stack with an integrated membrane-type humidification section is used to identify the system parameters and to validate the performance of the simulation model. The predicted thermal response is verified during typical variations in load, coolant flow, and coolant temperature. A first-law control volume analysis is performed to separate the relevant from the negligible contributions to the thermal dynamics and to determine the sensitivity of the energy balance to sensor errors and system parameter deviations.
Study on Autothermal Reforming of Diesel
Authors: Kang Inyong , Bae Joongmyeon
Published: October 2008

Diesel is one of the best hydrogen storage systems, which has very high volumetric density [kg H2/m3] (>100) and gravimetric density [%H2] (>15). Several catalysts were selected for diesel reforming. 3 catalysts (Pt on gadolinium doped ceria, Rh and Ru on the same support, Patent for catalyst formulation of Argonne National Laboratory in U.S.A) and 2 commercial catalysts (FCR-HC14 and FCR-HC35, Su¨d-Chemie, Inc.) were used to reform diesel. Pt catalyst showed the best performance. Effects of operating conditions such as temperature, O2/C and H2O/C on ATR (autothermal reforming) were investigated. In addition, we studied on reaction characteristics for better understanding about ATR reaction by analyzing concentrations of products and temperature profiles along catalyst bed. We found key issues such as fuel delivery and heat transfer between front exothermic part and rear endothermic part of catalyst bed.
Modeling and Simulation for PEMFC/Solar Panel Hybrid Vehicle With Solar Water Electrolysis System
Authors: Jee Hyunjin , Bae Joongmyeon
Published: October 2008

This Paper focuses on modeling and simulation to analyze the characteristic of PEMFC/solar panel hybrid vehicle and to evaluate algorithms for producing hydrogen by using PEMFC and solar panel. The system includes solar panel, water electrolysis, vehicle property, induction motor etc., and the fuel cell system is modeled with fuel cell irreversibility and dynamic response data obtained by the BCS Fuel Cell Inc.’s FC stack. In our model solar panel is used in parallel when a vehicle is driven to lower the electrical load of fuel cell stack. The solar panel is also modeled to be used to provide electricity to electrolysis system for hydrogen production. Matlab/Simulink package was used to evaluate and simulate the usefulness of the system in detail. According to the obtained simulation results, the extra power obtained from solar panel which has been explored in natural conditions of the Daejeon city, where the maximum value of solar radiation density in summer is equal to 900W/m2, can help to produce hydrogen and obtain the high efficiency of PEMFC according to dynamic load change in city drive mode. But the vehicle consumes more hydrogen than production, so hydrogen tank is required and solar water electrolysis system can make the tank smaller. It has to be noticed that this work is not focused on the efficiency and drive performance but on the explanation of algorithm and evaluation of hybrid vehicle’s usefulness.
Study of Dynamic Behavior for PEMFC Stack
Authors: Park Kwangjin , Bae Joongmyen
Published: October 2008

The dynamic behavior of a stack through experiment was compared with the simulation results of a dynamic model by using MATLAB/SIMULINK® for instantaneous change of power demand. The system consists of a 150W commercial fuel cell stack, humidifier, MFC and controller. The model was established with four basic equations. Model coefficients were calculated from experimental data and literatures. Polarization curve and dynamic responses showed similar behavior for both experimental and simulation results.
Lattice Boltzmann Simulations of Bubble Dynamics at the Anode of a µDMFC
Authors: Fei Kai , Cheng Chin-Hsien , Hong Che-Wun
Published: October 2008

This paper presents the bubble transport phenomenon at the anode of a micro direct methanol fuel cell (μDMFC) from a messooscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the μDMFC malfunction. Lattice-Boltzmann methods (LBM) were employed in this paper to simulate the two phase flow in a simplified micro channel which emulates the bubble dynamics in the porous diffusion layer and the flow channel. A two-dimensional, nine velocity model (D2Q9) was established. The surface tension, buoyancy force were treated as source terms in the momentum equation. Bounce back boundary conditions were assumed at the fluid-solid interface in this model. Simulation results and parametric studies showed that the pore size, the stream flow rate and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels.
Thermodynamic View on the Loss Mechanisms in PEM-Fuel Cells
Authors: Kabelac S. , Siemer M.
Published: October 2008

The fuel cell, which is a highly promising candidate for high efficiency energy conversion, is not reaching expected conversion efficiencies of η > 0,5 yet. Parallel to standard explanations of loss mechanisms by means of overvoltages, a thermodynamic view of addressing irreversibilities by calculating local entropy production rates is helpful. Entropy production rates are calculated by multiplying local transport fluxes with appropriate driving forces, i.e., gradients of temperature, chemical potentials and electric potentials. These gradients have to be calculated by solving the set of constitutive balance equations. Before this tedious task is done, simplified model equations have to be used. The reversible fuel cell is the starting point of analysis. Results for a one-dimensional PEMFC are shown.
Numerical Simulation of Coolant Electrolysis in Composite Plate PEM Fuel Cell Stacks
Authors: Peterson Amy , Im Kyoung-Su , Lai Ming-Chia
Published: October 2008

Two- and three- dimensional numerical models of a PEM fuel cell have been developed to investigate the effects of shunt current within the coolant channel. The model accounts for the electrostatic equation solved for a ten cell fuel stack for idealized and realistic coolant channels including varying conductivities of the solution. The electrostatic equation was solved in the coolant channel for the fully insulated, non-insulated, and incremental lengths of insulation on the channels. The model results found that the length of the insulation on the coolant channel plays an important role in shunt current reduction and fuel cell performance. The case of insulating the coolant channels was found to show that current density propagated further into the channels as increased lengths of insulation were used. However, the strength of the current density from the ending point of the insulation was found to decrease with increasing insulation lengths. Furthermore, a simple experiment was conducted idealizing the fuel cell as batteries connected in series and then submerged in a low conductivity solution. A camera was used to capture the current potential in the different “stacks” and to validate the numerical model.