bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments on Fault-Tolerant Active Vibration Control
Authors: Tao Tao , Byreddy Chakradhar , Frampton Kenneth D.
Published: October 2008

The purpose of this work is to experimentally demonstrate a fault-tolerant active vibration control system. Active vibration control is achieved using piezoceramic sensors and actuators (transducers) that are attached to a simply supported beam. These transducers are used by a set of optimal H2 feedback compensators to minimize the lateral vibration of a beam. Actuator faults are detected and isolated with a Beard–Jones fault detection filter. This filter is a special case of Luenberger observer, which produces a residual output with specific directional properties in response to a system fault. In this current research work, a new Beard–Jones filter design methodology is introduced that permits its use on high-order systems and also on systems with feed-through dynamics. The output of this detection filter is monitored by a hybrid automaton that determines when faults occur. This hybrid automaton then directs the selection of a feedback compensator specifically designed for the detected system fault state. The result is a vibration control system that is capable of maintaining optimal performance in the presence of system faults.
Time-Multiplied Guaranteed Cost Control of Linear Delay Systems
Authors: Wang Junling , Lam James , Xu Shengyuan , Shu Zhan
Published: October 2008

This paper investigates the design of guaranteed cost controllers for a class of linear systems with a state delay using a time-multiplied linear quadratic cost function. Based on delay-dependent and delay-independent stability criteria, guaranteed cost controllers can be constructed via solutions to linear matrix inequalities (LMIs) such that the resulting closed-loop system is stable and a specified time-multiplied linear integral-quadratic cost function has an upper bound. By the cone complementary linearization method, delay-dependent state feedback controllers can be derived in terms of LMIs. A numerical example is provided to demonstrate the effectiveness of the proposed method.
A Review of Proper Modeling Techniques
Authors: Ersal Tulga , Fathy Hosam K. , Rideout D. Geoff , Louca Loucas S. , Stein Jeffrey L.
Published: October 2008

A dynamic system model is proper for a particular application if it achieves the accuracy required by the application with minimal complexity. Because model complexity often—but not always—correlates inversely with simulation speed, a proper model is often alternatively defined as one balancing accuracy and speed. Such balancing is crucial for applications requiring both model accuracy and speed, such as system optimization and hardware-in-the-loop simulation. Furthermore, the simplicity of proper models conduces to control system analysis and design, particularly given the ease with which lower-order controllers can be implemented compared to higher-order ones. The literature presents many algorithms for deducing proper models from simpler ones or reducing complex models until they become proper. This paper presents a broad survey of the proper modeling literature. To simplify the presentation, the algorithms are classified into frequency, projection, optimization, and energy based, based on the metrics they use for obtaining proper models. The basic mechanics, properties, advantages, and limitations of the methods are discussed, along with the relationships between different techniques, with the intention of helping the modeler to identify the most suitable proper modeling method for a given application.
Unsteady Flow Simulation Through a Centrifugal Pump
Authors: Wu Yulin , Chen Naixiang , Xu Zhaohui , Liu Shuhong
Published: October 2008

Flow in a typical centrifugal pump is known to be unsteady due to flow instabilities and mutual interactions between the rotating part and the stationary parts. Flow instabilities are mostly viscous phenomena such as boundary layer separation and vortex shedding that produces relatively low frequency and small amplitude pressure fluctuations. Mutual interaction between the impeller blades and the guide vane diffuser produces relatively high frequency and large amplitude pressure fluctuations. This phenomenon is more closely related to compressibility than viscosity. It is important because it may cause structural vibration and noise. In this paper, the steady and unsteady turbulent flow through the whole flow passage of an entire centrifugal pump, has been computed to predict the pressure fluctuation of flow in the pump.
Numerical Modeling of Ducted Propellers
Authors: Kinnas Spyros A. , Lee Hanseong , Gu Hua
Published: October 2008

This paper presents two numerical methods, a Vortex-Lattice Method (VLM) based potential solver (named MPUF3A) coupled with a Finite Volume Method (FVM) based Euler solver (named GBFLOW), and a Boundary Element Method (BEM) based potential solver (named PROPCAV), which can predict the wetted and cavitating performance of ducted propellers. For the first approach, VLM is applied to model the propeller, and FVM is used to analyze the whole flow field with the duct. Those two methods are coupled together to include the interaction between duct and propeller. By distributing the line vortices and the line sources on the camber surface, MPUF3A solves the potential flow around the propeller, and as a result the pressure and cavitation patterns on the blade surface are determined. The duct is modeled as a solid boundary in GBFLOW which solves the Euler equations with body force term converted from pressures evaluated in MPUF3A. The solution of the Euler equation would bring the total velocity distribution. An effective wake field is determined by subtracting the induced velocity from the total velocity, and the predicted effective velocity is used by MPUF3A to predict the updated pressure distributions. In this way, both the duct (as solid boundary) and propeller (as body forces) are included in the fluid domain simultaneously and the flow and body forces are updated iteratively. The solution converges when the predicted thrust is stabilized within an acceptable tolerance. A general image model is applied to include the duct wall effect, and the viscous effect is modeled by the discharge model when the gap region between duct inner surface and propeller tip is small. For the second approach, a Boundary Element Method is applied to predict the cavitating performance of ducted propeller, in which the propeller and duct are paneled and solved simultaneously by applying the appropriate boundary conditions. The blade sheet cavity is determined by applying the dynamic and the kinematic boundary conditions on the cavity surface. The potential on the cavity surface is known from the dynamic boundary condition and the relation between cavitation number and cavity velocity. Once the boundary value problem is solved for the unknowns, i.e. the potentials on the wetted blade surface and the normal derivative of potentials on the cavity surface, the new cavity shape is adjusted by using the normal derivative of the potential. The procedure is repeated until the cavity shape converges and the pressure on the cavity becomes constant and equals to the vapor pressure. The present methods have been validated by comparing the predicted forces with those measured in experiments, and the cavity patterns and forces predicted from the two methods have been compared to each other.
Modeling and Analysis of a Pressure Compensated Flow Control Valve
Authors: Cheng Minter
Published: October 2008

In hydraulic systems, flow control valve is used to regulate the flow of fluid to actuators by adjusting the valve opening. However, the inlet and the outlet pressures of the valve are not always remaining constant. Any change in pressure will alter the flow rate through the valve and alter the actuator speed consequently. Pressure compensated flow control valves are often used in hydraulic systems when accurate speed control is required under varying supply or load pressures. The basic structure of the pressure compensated flow control valve is by incorporating a compensating spool to maintain a constant pressure drop across the metering orifice. Under ideal circumstance, the actuator speed can be constant and controllable, regardless of load or system pressure changes. However, in practical applications, any system or load pressures variations will cause force unbalance on valve compensating spool and affect the control accuracy. The steady and dynamic response of the flow control valve plays an important role on hydraulic system behavior. Therefore, analyzing and understanding of the valve steady and dynamic behaviors is very important. In this study, the steady and dynamic performance of a pressure compensated flow valve is simulated numerically by solving the characteristic equations. The parameters studied in this research are biased spring constant, pre-compressed spring length, spool mass, and the damping orifice characteristics. The simulation results show that the flow force is identified as the key factor to affect the control accuracy. Increasing the spring constant as well as the pre-compressed spring length will increase the steady flow rate and reduce the transient response time. Decreasing the damping orifice opening or the discharge coefficient will increase the transient response time. The spool mass has practically no effect on the flow rate.
Complex Flow Dynamics in Dense Granular Flows: Part I — Experimentation; Part II — Simulations
Authors: Zamankhan Piroz
Published: October 2008

PART I: By applying a methodology useful for analysis of complex fluids based on a synergistic combination of experiments, computer simulations and theoretical investigation, a model was built to investigate the fluid dynamics of granular flows in an intermediate regime where both collisional and frictional interactions may affect the flow behavior. In Part I, the viscoelastic behavior of nearly identical sized glass balls during a collision, have been studied experimentally using a modified Newton’s Cradle device. Analyzing the results of the measurements, by employing a numerical model based on finite element methods, the viscous damping coefficient was determined for the glass balls. Power law dependence was found for the restitution coefficient on the impact velocity. In order to obtain detailed information about the interparticle interactions in dense granular flows, a simplified model for collisions between particles of a granular material was proposed to be of use in molecular dynamic simulations, discussed in Part II. PART II: By applying a methodology useful for analysis of complex fluids based on a synergistic combination of experiments, computer simulations, and theoretical investigation, a model was built to investigate the fluid dynamics of granular flows in an intermediate regime, where both collisional and frictional interactions may affect the flow behavior. In Part I, experiments were described using a modified Newton’s Cradle device to obtain values for the viscous damping coefficient, which are scarce in the literature. In this paper, molecular dynamic simulations were performed using the simplified model for collisions between particles, developed in Part I, to obtain detailed information about the interparticle interactions. This information was used to develop a continuum model for granular flows, accounting for both collisional and frictional interactions between particles. To validate the continuum model, simulations were performed for the specific case of granular flow in a rapidly spinning bucket. The model was able to reproduce experimentally observed flow phenomena in buckets spinning at high frequencies (higher than 50 Hz), such as the transition from a cusp to a depression in the center of the bucket with increasing rotation rate. This agreement suggests that the model may be a useful tool for the prediction of dense granular flows in industrial applications, but highlights the need for further experimental investigation of granular flows in order to refine the model.
Comparison of Computational Results Obtained From a VOF Cavitation Model With Experimental Investigations of Three Inducers: Part I — Experimental Investigations; Part II — Numerical Analysis
Authors: Mejri Imene , Bakir Farid , Rey Robert , Belamri Thabet
Published: October 2008

The paper presents full 3D numerical simulations and experimental investigations of the cavitating flow through three axial inducers. These inducers are identified by the blades leading edge angle at the periphery β1T = 8°, 10°, 13° and are thus noted as Inducer 8°, Inducer 10° and Inducer 13°. They have the same tip and hub diameters. The numerical and experimental investigations were carried out at the LEMFI-Paris laboratory. This enabled us to explain the cavitating operation for off-design conditions. In Part I of this paper we describe the design methodology adopted for the inducers and which is deduced from literature and in house experience. Then the main experimental results are presented for the studied inducers at a range of flow rates and cavitation numbers concerning: • The overall performances: pressure head coefficient and efficiency versus several flow rates. • Critical cavitation number (5% and 15% of drop) versus the flow rate. In Part II of this paper, a review of the cavitating regime modeling and the cavitation VOF model used for this paper’s calculations is firstly presented. The numerical approach is based on a combination of the VOF technique with a truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse processes of bubbles. The cavitation model also features a control volume finite element discretization and a solution methodology which implicitly couples the continuity and momentum equations together. The numerical results of Part II concern: • The overall performances. • The numerically investigated water vapor volume fraction distributions and other CFD results, which enable us to explain the cavitating behavior for these inducers. • The location and sizes of the blade cavity and backflow vortex. Finally, the comparisons between experimental and simulated results on the overall performances, cavities sizes and cavities location are discussed. A good agreement between experimental and predicted results was found for a range of flow rates. The head breakdown in the simulations started at a different cavitation coefficient than that in the experiment.
Experimental Measurements and Numerical Simulations of Two-Phase Stratified, Wavy and Slug Flow in a Narrow Rectangular Channel
Authors: O’Halloran Steven P. , Beck B. Terry , Hosni Mohammad H. , Eckels Steven J.
Published: October 2008

Flow pattern transitions in two-phase flow are important phenomena for many different types of engineering applications, including heat exchangers. While two-phase flow is not understood as well as single-phase flow, advancements in both measurement techniques and numerical simulations are helping to increase the understanding of two-phase flow. In this paper, stratified/wavy flow is investigated, along with the transition from wavy to slug flow. For the experimental setup, a narrow channel with a length of 600 mm, height of 40 mm, and a width of 15 mm was fabricated using clear acrylic plastic, and water and air were the two fluids used for testing. The water in the channel was initially at rest, and the transition in flow patterns was created by increasing the velocity of air flowing over the water surface. Particle image velocimetry (PIV) was used to measure the velocity of the flow for stratified and wavy flow conditions, and also the velocity at the onset of slug flow. Along with the experimental measurements, computational fluid dynamics (CFD) simulations were conducted on a similar geometry using the volume of fluid (VOF) two-phase model. A commercial CFD software package was used for the simulations, and comparisons were made between the experimental measurements and numerical results. Favorable agreement was found between the experimental measurements and the numerical simulations. In particular, the transition from wavy to slug flow compared well to previously developed two-phase flow transition models, including the slug transition developed by Taitel and Dukler.
An Experimental Study of Blade Angle Effect on a Micro Axial-Type Turbine Air Grinder
Authors: Cho Soo-Yong , Choi Sang-Kyu , Cho Chong-Hyun
Published: October 2008

Performance characteristics are experimentally studied with changing nozzles, stators and rotors on a partially admitted small axial-type turbine, which could be applied to a driver of micro air grinders. When air tools adopt axial-type turbines as a driver, they could operate without friction and abrasion because the turbine rotor does not make contact with the casing. In order to maintain these merits on a small axial-type turbine without reducing power, performance characteristics are examined in this study through measuring the specific output power with eight different stators and three different rotors and nozzles. The tested turbine consists of two-stages and its mean radius of flow passage is 9.2mm. Output powers are obtained through measured pressure, temperature, torque, rotational speed, and flow rate. The experimental results show that the output power obtained on the second stage is insignificant comparing with that on the first stage because partially admitted flow is fully diffused in the second stage. Meanwhile, the output power is increased to 16–22% by changing the nozzle blade angle from 60° to 70° because the first stage performance is directly affected by the flow spouted from the nozzle. These results indicate that blade angles greatly influence the performance of a micro turbine operating in partial admission. When an appropriate stator and rotor that are designed in accordance with the flow spouted from the nozzle are installed in the rotating part, the output power is increased to 38% depending on the blade angle.
Flow in Atomizers: Influence of Different Parameters on the Performance Characteristics of Plain Orifice Atomizer and Pressure Swirl Atomizer of a Fuel Injection System of Gas Turbine Combustor
Authors: Kulshreshtha Digvijay B. , Channiwala S. A.
Published: October 2008

The atomization process is essentially one in which bulk liquid is converted into small drops. Basically, it can be considered as a disruption of the consolidating influence of surface tension by the action of internal and external forces. In the absence of such disruptive forces, surface tension tends to pull the liquid into the form of a sphere, since this has the minimum surface energy. Liquid viscosity exerts a stabilizing influence by opposing any change in system geometry. On the other end, aerodynamic forces acting on the liquid surface may promote the disruption process by applying an external distortion force to the bulk liquid. Breakup occurs when the magnitude of the disruptive force just exceeds the consolidating surface tension force. In twin fluid atomizers of the air-blast type and air assist type, atomization and spray dispersion tend to be dominated by air momentum forces, with hydrodynamic processes playing only a secondary role. With pressure swirl nozzles, the internal flow characteristics are of primary importance, because they govern the thickness and uniformity of the annular liquid film formed in the final discharge orifice as well as the relative magnitude of the axial and tangential components of velocity of this film. It is therefore of great practical interest to examine the interrelationships that exist between internal flow characteristics, nozzle design variables, and important spray features such as cone angle and mean drop size. The various equations that have been derived for nozzle discharge coefficient are discussed because this coefficient not only affects the flow rate of any given nozzle but also can be used to calculate its velocity coefficients and spray cone angle. Consideration is also given to the complex flow situations that arise on the surface of a rotating cup or disk. These flow characteristics are of basic importance to the successful operation of atomizers, because they exercise a controlling influence on the nature of the atomization process, the quality of atomization, and distribution of drop sizes in the spray. For plain orifice atomizers, the key geometrical variables are the orifice length and diameter. Final orifice diameter is of prime importance for pressure swirl atomizers. The absence of any theoretical treatment of the atomization process has led to the evolution of empirical equations to express the relationship between the mean drop size in a spray and the variable liquid properties. This paper includes the study of different parameters that affect the flow in plain orifice and pressure swirl atomizers. The paper also includes the performance characteristics of plain orifice and pressure swirl atomizers.
Numerical Simulations of Turbulent Flume Heat Transfer at Pr = 5.4: Impact of the Smallest Temperature Scales
Authors: Bergant R. , Tiselj I.
Published: October 2008

In the present paper a role of the smallest diffusive scales of a passive scalar field in the near-wall turbulent flow was examined with pseudo-spectral numerical simulations. Temperature fields were analyzed at friction Reynolds number Reτ = 170.8 and at Prandtl number, Pr = 5.4. Results of direct numerical simulation (DNS) were compared with the under-resolved simulation where the velocity field was still resolved with the DNS accuracy, while a coarser grid was used to describe the temperature field. Since the smallest temperature scales remained unresolved in this simulation, an appropriate spectral turbulent thermal diffusivity was applied to avoid pileup at higher wave numbers. In spite of coarser numerical grid, the temperature field is still highly correlated with the DNS results, and thus point to practically negligible role of the diffusive temperature scales on the macroscopic behavior of the turbulent heat transfer.
Dynamical States of Bubbling in Vertically Vibrated Granular Materials: Part I — Collective Processes; Part II — Theoretical Analysis and Simulations
Authors: Bordbar Mohammad Hadi , Zamankhan Piroz
Published: October 2008

PART I: Granular materials deform plastically like a solid under weak shear and they flow like a fluid under high shear. These materials exhibit other unusual kinds of behavior, including pattern formation in shaking of granular materials for which the onset characteristics of the various patterns are not well understood. Vertically shaken granular materials undergo a transition to a convective motion which can result in the formation of bubbles. In Part I, a detailed overview is presented of collective processes in gas-particle flows useful for developing a simplified model for molecular dynamic type simulations of dense gas-particle flows. The large eddy simulation method (LES) has been employed for simulating fluid flows through irregular array of particles. The results obtained may lead to scale-dependent closures for quantities such as the drag, stresses and effective dispersion. These are of use for developing a continuum approach for describing the deformation and flow of dense gas-particle mixtures described in Part II. PART II: Granular materials deform plastically like a solid under weak shear and they flow like a fluid under high shear. As discussed in Part I, these materials exhibit other unusual kinds of behavior, including pattern formation in shaking of granular materials for which the onset characteristics of the various patterns are not well understood. Vertically shaken granular materials undergo a transition to a convective motion which can result in the formation of bubbles. In this part, hydrodynamic continuum equations are presented for describing the deformation and flow of dense gas-particle mixtures. The constitutive equation used for the stress tensor provides an effective viscosity with a liquid-like character at low shear rates and a gaseous-like behavior at high shear rates. The numerical solutions are obtained for the aforementioned hydrodynamic equations for predicting the flow dynamics of dense mixture of gas and particles in a vertical cylindrical container, whose base wall is subjected to sinusoidal oscillation in the vertical direction given as z = A sin(kvx) sin(lvy) cos(ωvt), where (ωv = Clv2+kv2), C is speed of wave in base wall of container, A is a constant, and kv = mvπ and lv = nvπ. For a heptagonal prism shaped container under vertical vibrations, the model results were found to predict bubbling behavior analogous to those observed experimentally. This bubbling behavior may be explained by the unusual gas pressure distribution found in the bed. In addition, oscillon type structures are found to be formed using a vertically vibrated, pentagonal prism shaped container. The latter, however, seems to strengthen the observation that the pressure distribution plays a key role in deformation and flow of dense mixtures of gas and particles under vertical vibrations.
Development of a Web-Based Interactive Compressible Flow Solver
Authors: Eletem H. , Young F. , Aung K.
Published: October 2008

Compressible flow is an important subject in aerospace and mechanical engineering disciplines. This paper describes the development of a web-base interactive compressible flow solver using Java programming language. The main objective of the solver is to provide students with a software tool than can be used in the compressible flow course offered in the Department of Mechanical Engineering at Lamar University. The solver has a graphical user interface (GUI) for ease of use and interactivity. The solver was developed with the intention of free distribution to the educational community and other interested users.
Case Study of the Hydraulic Design of a Suction Chamber: CFD Calculation and Its Traps
Authors: Op de Woerd J. G. H. , Dijkers R. J. H. , Kru¨s H.
Published: October 2008

For a large sewage pumping station a suction chamber is designed to deliver fluid free of rotation and with an equal velocity field distribution to the inlet of the pump impeller. Tight geometrical constraints have been incorporated in a new design for the pump suction layout. During the first step in the design process the suction layout of successively placed bend, diffuser, bend and suction chamber have been designed. This design step is validated by means of three-dimensional flow analysis. From the CFD analysis different performance parameters are computed and the geometry is fine-tuned. Finally a scaled down air test is executed to verify and analyze the performance of the design. The design, CFD analysis and scaled down air test of the suction chamber will be described in this paper. It will be shown that flow patterns will not in all cases be correctly predicted from CFD analysis and that in many cases validated experience is needed to give the designer full confidence in the performance of the design.
Measurements and Modeling of Particle Sedimentation Rate and Settling Velocity in a Vertical Pipe
Authors: Li Qian , Shirazi Siamack A. , McLaury Brenton S. , Kouba Gene , Song Shanhong
Published: October 2008

A mechanistic model has been developed to predict settling velocity in a vertical pipe, and a finite-difference model has been developed to predict particle sedimentation rates. Experiments have been conducted in a vertical pipe filled with water or white oil to observe the different sedimentation regimes and measure the particle sedimentation rates for model verification. Particles used in the experiments were sand and glass beads. A two-pipe apparatus and a one-pipe apparatus were used. Several sedimentation phenomena were observed including, dilute particle settling, clustered settling, hindered settling, and particle bridging phenomenon. Good agreement in rate of sand bed buildup was found between the model and data in the one-pipe apparatus.
Assessing the Effects of Near Wall Corrections of the Force Acting on Particles in Gas-Solid Channel Flows
Authors: Arcen Boris , Tanie`re Anne , Oesterle´ Benoiˆt
Published: October 2008

The importance of using the lift force and wall-corrections of the drag coefficient for modeling the motion of solid particles in a fully-developed channel flow is investigated by means of direct numerical simulation (DNS). The turbulent channel flow is computed at a Reynolds number based on the wall-shear velocity and channel half-width of 185. Contrary to most of the numerical simulations, we consider in the present study a lift force formulation that accounts for the weak and strong shear as well as for the wall effects (hereinafter referred to as optimum lift force), and the wall-corrections of the drag force. The DNS results show that the optimum lift force and the wall-corrections of the drag together have little influence on most of the statistics (particle concentration, mean velocities, and mean relative and drift velocities), even in the near wall region.
Numerical Simulations of Laminar Backward-Facing Step Flow With FEMLAB 3.1
Authors: Gualtieri Carlo
Published: October 2008

The paper presents 2-D numerical simulations of laminar backward-facing step flow using the FemLab 3.1 modeling package. Results demonstrated that primary reattachment lengths predicted by FemLab were in close agreement with experimental data up to step Reynolds number Reh = 300. Also, dimensionless velocity profiles along the channel height calculated by FemLab were successfully compared with the experimental data.
Investigation of the Flow Field in a Multistage Pump by Using LES
Authors: Nagahara Takahide , Inoue Yasuhiro , Sato Toshiyuki , Sakata Shinji , Nishimura Kazumi , Kato Chisachi
Published: October 2008

Unsteady numerical calculation of an entire multistage pump was performed by using a large eddy simulation (LES) at the design flow rate to investigate the flow field in the pump in detail and to evaluate the accuracy of LES by comparing the results with an experimental and a conventional CFD result based on a Reynolds-averaged Navier-Stokes (RANS) equation. We investigated a four-stage centrifugal pump consisting of a suction bend, impellers, vaned diffusers, return channels, and a discharge volute. The interaction between the impeller and the stator was taken into account by using a moving overset grid in LES calculations, and the flow field in the inlet portion of each hydraulic part was investigated using the calculated result. In the experimental investigation, velocity distributions and pressure fluctuation were measured at several points by using a scaled model pump. RANS calculation was performed with respect to a single-stage pump composed of the first-stage component of the four-stage pump. We found that the hydraulic design of the four-stage pump is satisfactory and that LES was a very effective design tool for investigating the flow field in detail including the unsteadiness in the hydraulic passageway of the multistage pump.
Optimization of Approach Flow Conditions of Vertical Pumping Systems by Physical Model Investigation
Authors: Scha¨fer F. , Hellmann D.-H.
Published: October 2008

Circulating flow in front of open and covered intake systems in many cases is the initial point of free-surface vortex formation. Depending on the strength of the circulation air pulling vortex formation up to a coherent air core will appear starting at the surface leading directly to an installed pump inside the intake. Thus the mechanical load of the pump will increase and the hydraulic performance will be degraded. Furthermore, pre-rotation of the fluid close to the suction bell can be forced up to limits which are not in compliance to state of the art acceptance criteria. At least non-symmetric velocity distribution at the impeller will arise out of this flow conditions. Within physical model tests intakes together with pumps can be optimized for their best efficiency point of operation. Flow conditions can be achieved generating kinematical affinity at the suction bell which are close to the conditions of the acceptance test. The report shows application oriented solutions for the installation of cost effective flow guiding devices in open and covered intake systems to assure adequate pump performance. Test results of model investigations and experiences by modifying intake structures of existing plants will be presented. Concerning the sensitivity of high specific speed vertical pumps approach flow conditions especially at the intake structures have to be in accordance to state of the art acceptance criteria to assure adequate availability of the pumps. By today it is common practise and state of the art to test the behaviour of intake and outfall structures by physical model tests.
Prediction and Improvement of Artificial Ground Freezing
Authors: Yokoo M. , Shibazaki M. , Yoshida H. , Souma H. , Ousaka A. , Kusano K. , Horii K.
Published: October 2008

The aim of present study is to establish the numerical model for the solidification or melting of water saturated soil and to clarify the effect of thermal and physical parameters on the artificial soil freezing by comparing between the numerical and experimental results. First, the numerical model has been modified to adapt for freezing of soil. By comparing between obtained numerical solutions and experimental data, the validity of the model has been checked and certified. Next, the effect of physical property of soil, initial and boundary conditions of soil and freezing pipes, the velocity of groundwater, and the arrangement of freezing pipes on soil freezing have been examined. As the results, it was found that the water content of soil and ground water affect the volume of solid, besides the groundwater also especially changes the profile of solid/liquid interface. The rate of the interface growth would gradually stop provided that the flow speed exceeds certain limits. The knowledge obtained from our study will be useful to predict solid volume, decrease in thermal energy consumption and minimize the influence to ambience on artificial ground freezing precisely.
Numerical Simulation of Flow and Heat Transfer of LCD Projector Using Voxel Method
Authors: Isoshima N. , Watanabe M. , Saito H.
Published: October 2008

We developed a voxel code using a finite difference method for unsteady three-dimensional thermal flows in a Cartesian grid system. This code enables us to predict flow fields around complicated geometries in a short pre-processing time. The code was used to predict flow fields around a flat plate that was heated to a constant temperature, and the results were within 20% of those obtained using analytical solutions. The code was also used to predict the flow field of a liquid crystal display (LCD) projector that has highly complicated internal structures such as a lamp, LCD panels, electric parts, etc.
Virtual Prototyping of Advanced Fan Designs With Computational Fluid Dynamics
Authors: Lees Paul , Koelman Onno , Kadakia Chetan
Published: October 2008

This paper describes the application of computational fluid dynamics (CFD) to fan design as part of the PAX Scientific product development cycle. Six-inch fans are investigated using a simulation configuration designed to match in-house testing facilities. Grid generation and flow simulations are carried out using a commercial CFD software (Fluent). The segregated solver is used to run steady state RANS simulations with a Realizable k-ε turbulence scheme. Performance predictions (flow and pressure generated, power required) are in agreement with experimental testing values, with a margin of error ranging from less than 1% to less than 10%.
Analysis of Supersonic Turbulent Boundary Layers Over Rough Surfaces Using the K-Omega and Stress-Omega Models
Authors: Guo Guanghong , Sharif M. A. R.
Published: October 2008

In this study, the influence of surface roughness in the prediction of the mean flow and turbulent properties of a high-speed supersonic (M = 2.9, Re/m = 2.0e7) turbulent boundary layer flow over a flat plate is performed using the k-ω and the stress-ω models. Six wall topologies, including a smooth and five rough surfaces consisting of three random sand-grain plates and two uniformly machined plates were tested. Experimental data are available for these configurations. It is observed that, for smooth surface, both k-ω and stress-ω models perform remarkably well in predicting the mean flow and turbulent quantities in supersonic flow. For rough surfaces, both models matched the experimental data profiles fairly well for lower values of the roughness height. Overall, the k-ω model performed better than the stress-ω model. The stress-ω model did not show any strong advantages to make up for the extra computational cost associated with a Reynolds stress model. The simulation results indicated that the prescription for the surface boundary conditions for ω in both models, especially for the stress-ω model, need to be refined encountering high roughness numbers and reconsidered to include the geometric factor.
Effect of Inlet Curvature on the Discharge Coefficients of Toroidal-Throat Critical-Flow Venturi Nozzles (Keynote)
Authors: Ishibashi Masahiro , Morioka Toshihiro , Arnberg B. Thomas
Published: October 2008

The effect of the inlet curvature R on the discharge coefficients of toroidal throat critical flow Venturi nozzles is discussed based on calibration results of high-precision nozzles HPNs with R = 1.0, 1.2, 1.5, 1.8, 2.0, and 2.5D, where D is the throat diameter (9.6, 13.4, and 18.9 mm). The Reynolds numbers RD range from 1.2×105 to 1.2×106, corresponding to absolute upstream pressures of 0.1 to 0.7 MPa. The calibrations were performed by a constant volume tank system developed for the primary standard in Japan.
A P.I.V. Processing Technique for Directly Measuring Surface-Normal Velocity Gradient at a Free Surface
Authors: Phan Tuy N. M. , Nguyen Chuong V. , Wells John C.
Published: October 2008

Compressive surface-normal velocity gradient at a free surface leads to high mass transfer across a free surface. Our research aims to directly measure this velocity gradient at the free surface by proposing an advanced Particle Image Velocimetry (PIV) technique and simultaneously evaluate its applicability. This technique, PIV/IG (Interface Gradiometry), was proposed by Nguyen et al. (2004) to directly measure wall velocity gradient with high S.N.R. Herein, we adapt this technique to measure the compressive surface-normal velocity gradient at the free surface of open channel flow with minimal fluctuation of water surface. We validate this technique in a two-component PIV configuration by synthetic PIV images corresponding to uniform compression, linearly-varying compression, and a velocity field based on DNS data of open channel flow at friction Reynolds number Reτ = 240 and zero Froude number. The results clearly show that this technique works much better than the velocity differentiation method. The effect of template size on the measured value is evaluated.
Experiments Toward Fundamental Validation of PEM Fuel Cell Models
Authors: Yan Q. G. , Liu Q. Y. , Toghiani H. , Wu J. X.
Published: October 2008

Detailed experimental parameters are controlled and measured under widely varying operating conditions. In addition to polarization curves, feed gas flow rates, temperatures, pressure drop, and relative humidity are all measured accurately. Performance of a polymer electrolyte fuel cell (PEFC) was studied using steady-state polarization curves and electrochemical impedance spectroscopy (EIS) techniques. The effects of relative humidity, temperature, pressure and feed gas stoichiometry on fuel cell performance were investigated. It was found that the humidity of both the anode and cathode inlet gases had a significant effect on fuel cell performance. The experimental results showed that a decrease in the cathode humidity has a more detrimental effect on cell performance than a comparable decrease in the anode humidity. The obtained results will be used to define conditions of optimal hydration of the membrane. Based on the performance and resistance measurements, optimal humidification can be achieved. The polarization curves of the cell at different operating temperatures showed that fuel cell performance was improved with increasing temperature from 65 to 75°C. The fuel cell performance also improved as the operating pressure was increased from 1 atm to 4 atm. The resistance of the working fuel cell showed that the membrane resistance increased as the feed gas relative humidity (RH) decreased. The experimental results were compared with the results of a CFD mathematical model. These experimental data will provide a baseline for validation of fuel cell models.
Dynamic Simulation of an Integrated Solid Oxide Fuel Cell System Including Current-Based Fuel Flow Control
Authors: Mueller Fabian , Brouwer Jacob , Jabbari Faryar , Samuelsen Scott
Published: October 2008

A two-dimensional dynamic model was created for a Siemens Westinghouse type tubular solid oxide fuel cell (SOFC). This SOFC model was integrated with simulation modules for other system components (e.g., reformer, combustion chamber, and dissipater) to comprise a system model that can simulate an integrated 25 kilowatt SOFC system located at the University of California, Irvine. A comparison of steady-state model results to data suggests that the integrated model can well predict actual system power performance to within 3 percent, and temperature to within 5 percent. In addition, the model predictions well characterize observed voltage and temperature transients that are representative of tubular SOFC system performance. The characteristic voltage transient due to changes in SOFC hydrogen concentration has a time scale that is shown to be on the order of seconds while the characteristic temperature transient is on the order of hours. Voltage transients due to hydrogen concentration change are investigated in detail. Particularly, the results reinforce the importance of maintaining fuel utilization during transient operation. The model is shown to be a useful tool for investigating the impacts of component response characteristics on overall system dynamic performance. Current-based flow control (CBFC), a control strategy of changing the fuel flow rate in proportion to the fuel cell current is tested and shown to be highly effective. The results further demonstrate the impact of fuel flow delay that may result from slow dynamic responses of control valves, and that such flow delays impose major limitations on the system transient response capability.
Optimization of the PEM Fuel Cell Cooling System by Entropy Generation Minimization
Authors: Sharifian L. , Saidi M. H.
Published: October 2008

Cooling system is essential for high power fuel cells to maintain cells temperature in an acceptable limit. In this paper a suitable cooling system for the PEM fuel cell has been designed and optimized. The design includes the number of the cooling plates, the proper circuit of the cooling channels in the plates, the channel dimensions, the flow rate of the cooling fluid and its temperature. The optimization technique is minimization of the entropy generation through the cooling plates. The design of the cooling channels and plates is such that the plate temperature doesn’t exceed from a desired temperature and the temperature variation in the plate becomes minimized. In this design, the coolant has a minimum pressure drop and the system needs minimum pumping power.
Preparation of Platinum Supported on Carbon Blacks With Different Surface Chemical Characteristics
Authors: Jia Rong-Li , Wang Cheng-Yang , Zhu Bin
Published: October 2008

In a study of the preparation of Pt/C eletrocatalysts, a set of modified Vulcan XC-72R carbon black supports have been prepared by nitric acid or hydrogen peroxide oxidation, or thermal treatment in nitrogen flow. The supports obtained by these methods had largely identical pore structure, but different from the amount of surface oxygen-containing groups. The physical and surface chemical nature of the supports was characterized by XPS, BET, FTIR and acid-base titration. The above pre-treatment-carbon supported platinum catalysts were prepared by impregnation-reduction method with formaldehyde as the reducing agent, H2PtCl6 as precursor. The effect of the amount of surface oxygen-containing groups of Vulcan XC-72R carbon black on Pt/C catalysts dispersion was studied by the characterization with XRD and TEM. It has been found that decreasing the amount of surface oxygen-containing groups on carbon supports favored the platinum dispersion on the Pt/C catalysts.
Development of the BOP Bench System for PEM Fuel Cell Vehicles at Hyundai MOBIS
Authors: Ahn Sang-Yeoul , Jeon Ui-Sik , Ahn Byung-Ki
Published: October 2008

We have developed a BOP test bench of 80kW-class PEMFC systems to evaluate the performance and optimize the size of the core components of the BOP for fuel cell vehicles. The BOP components including heat exchangers, water pumps, deionizers, and compressors are connected to provide the reactant gases and the coolant to a mock-up stack which is designed to reasonably simulate the electrochemical phenomena of an actual stack. Sensors and actuators are installed between the inlets and outlets of the components, and are connected to the data acquisition and control systems to control pressure, temperature, flow rate and humidity of the used fluids.
An Analytical Model of the Membrane Electrode Assembly in a PEMFC
Authors: Litster S. , Djilali N.
Published: October 2008

An analytical model of the membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell (PEM) has been developed for investigating the effect of catalyst layer specifications. Emphasis is placed on the cathode catalyst layer, which is modeled using a finite-thickness formulation with parameters obtained from a variable-width macrohomogeneous model. The variable-width formulation accounts for the effect of changing catalyst layer specifications on the dimensions of the catalyst layer by assuming a constant void fraction. Interest in low-humidity operation of micro-fuel cells that are passively fed ambient air has facilitated the present derivations and assumptions. The model is shown to agree well with experimental data over a substantial range of catalyst layer specifications. In addition, the model shows excellent promise as a tool for optimizing catalyst layers in micro-fuel cells with passive ambient air breathing.
Fuel Cells and Cogeneration
Authors: Parise J. A. R. , Vargas J. V. C. , Pitanga Marques R.
Published: October 2008

Although historically grown as independent energy technologies, fuel cell and cogeneration may adequately work to each other’s benefit. Some fuel cells deliver heat at sufficiently high temperatures, which can be certainly used as heat sources for cogeneration or trigeneration schemes. The paper presents an overview of the innumerable combinations of the simultaneous production, with fuel cells, of (i) heat and power, (ii) cold and electricity, and (iii) cold, heat and electricity, in its multiple varieties. The survey included combined power cycles (also called hybrid systems) where the fuel cell works together with other thermodynamic cycles to produce, with a high fuel-to-electricity efficiency, electricity alone. A large number of cogeneration arrangements are mentioned. Some are described in detail. A brief analysis of benefits and drawbacks of such systems was undertaken. The review was limited to articles published in archival periodicals, proceedings and a few technical reports, theses and books.