bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Single Drops in a Vertical Pipe Using Various Coordinate Systems
Authors: Hirokawa Keishun , Hayashi Kosuke , Sou Akira , Tomiyama Akio , Takada Naoki
Published: March 2009

The effects of the diameter ratio λ (= d/D, where d and D are the diameters of a drop and a pipe, respectively), the Morton number M and the viscosity ratio κ (= μd/μc, where μ is the viscosity and the subscripts d and c are the dispersed fluid particle and the continuous phase, respectively) on terminal velocities and shapes of single drops rising through stagnant liquids in a vertical pipe are investigated experimentally. Then, the drops in the pipe are simulated using a volume tracking method with various coordinate systems, i.e., three-dimensional (3D) cylindrical coordinates, 3D general curvilinear coordinates and 3D Cartesian coordinates. Predicted velocities and shapes of the drops using three coordinate systems are compared with the measured data to examine the effects of coordinate systems on the accuracy of prediction. As a result, (1) The velocity ratio VT/VT0 (VT and VT0 are the terminal velocity in a pipe and infinite liquid, respectively) decreases as λ increases, and it depends not only on λ but also on M and κ, (2) Good predictions for the terminal velocities and shapes of drops are obtained not only with cylindrical coordinates and curvilinear coordinates but also with Cartesian coordinates, provided that the spatial resolution is high, (3) When the spatial resolution is low, effects of coordinate systems on a drop shape are larger for Cartesian coordinate systems than for cylindrical coordinate and general curvilinear coordinate systems, and (4) Errors in predicted drop velocities are not so large even with very low spatial resolution.
Accuracy of Ultrasonic-Measurement-Integrated Simulation for Three-Dimensional Blood Flow in Aneurysmal Aorta
Authors: Funamoto K. , Hayase T. , Saijo Y. , Yambe T.
Published: March 2009

The Ultrasonic-Measurement-Integrated (UMI) simulation, in which feedback signals proportional to the optimal estimation of the difference in velocity vector against real blood flow obtained by Doppler velocities are applied at grid points in the feedback domain, has been developed to reproduce complicated hemodynamics. This paper evaluates UMI simulation for three-dimensional unsteady blood flow in aneurysmal aorta. We performed a numerical experiment of UMI simulation with an unsteady standard solution of the three-dimensional blood flow in an aneurysmal aorta with a realistic boundary condition. The UMI simulation was performed with an inaccurate boundary condition and various feedback arrangements assuming the acquisition of Doppler velocities in the aneurysmal domain or feedback domain. The application of feedback made the computational result approach to the standard solution, so that UMI simulation estimated the hemodynamic stresses more correctly than the ordinary simulation. Hence, UMI simulation of real blood flows will bring significant benefits for the clinical diagnosis and treatment of circulatory diseases.
Direct Numerical Computation of the Lift Force on Single Bubbles
Authors: Bothe Dieter , Schmidtke Martin , Warnecke Hans-Joachim
Published: March 2009

In addition to experimental investigations, computational fluid dynamics is frequently applied to obtain a better understanding of multiphase flows in industrial devices. An accurate simulation of the bubbles’ movement requires detailed knowledge of the interacting forces between gas and liquid phase. In typical gas-liquid flows, bubbles rise in non-homogenous velocity fields. In this case, the bubbles experience a so-called lift force which causes them to migrate sideward, while they are rising. In air-water systems, small spherical bubbles usually drift into the direction of higher counter-flow, whereas larger, more deformed bubbles drift in the opposite direction. In this contribution, we present numerical simulations of single bubbles rising in linear shear flows. The influence of bubble size and shape on the lift force is shown and the results are compared with experimental investigations carried out by Tomiyama and co-workers [1]. The simulations are performed with the MPI-parallelized code FS3D (Free Surface 3D) which employs an advanced Volume-of-Fluid method to resolve free and deformable gas-liquid interfaces [2]. FS3D was developed at the ITLR, University of Stuttgart and extended in our group for the current studies. Bubble size and material data are varied, and the corresponding lift forces in a linear shear flow are calculated by evaluation of the bubble trajectories.
Numerical Solution of the Navier-Stokes Equations for Unsteady Magnetohydrodynamic Flow Between Two Parallel Porous Plates
Authors: Ganesh S. , Krishnambal S.
Published: March 2009

The Unsteady Laminar flow of an electrically conducting viscous, incompressible fluid between two parallel porous plates of a channel in the presence of a transverse magnetic field when the fluid is being withdrawn through both the walls of the channel at the same rate is discussed. Numerical solution is obtained for different values of R (Suction Reynolds number) using R-K Gill’s method and the graphs of dimensionless functions f′ and f have been drawn.
Movement of Solid Particles on Bottom of an Unbaffled Vessel Agitated by Unsteadily Forward-Reverse Rotating Impeller
Authors: Yoshida Masanori , Kimura Akihiro , Yamagiwa Kazuaki , Ohkawa Akira , Tezura Shuichi
Published: March 2009

An unbaffled agitated vessel having an unsteadily rotating impeller was employed as an apparatus mixing liquid and solid particles with the density larger than that of liquid. For this type of vessel, the movement of solid particles on the vessel bottom was studied in relation to the liquid flow produced by the impeller. When a disk turbine impeller with six flat blades was rotated in the forward-reverse mode, the liquid flow and the particle movement were visualized. Concurrently, the agitation requirement for complete solid suspension where no particle remains on the vessel bottom for more than a short period and all particles are in motion was determined as a minimum rotation rate of impeller. The liquid flow and the particle movement around a tiny heap of solid particles configured on the vessel bottom were characterized through measurement of their velocities by the particle tracking velocimetry (PTV). The relative velocity of rising with off-bottom suspension of solid particles was uniform in its distribution and wholly large in its magnitude, compared with that in a baffled vessel with a unidirectionally rotating impeller of the identical design, which revealed an effectiveness of this type of vessel as an apparatus for the solid-liquid mass transfer.
Fluid Mixing Control Inside a Y-Shaped Microchannel by Using Electrokinetic Instability
Authors: Jin Zheyan , Hu Hui
Published: March 2009

An experimental study was conducted to further our understanding about the fundamental physics of electrokinetic instability (EKI) and to explore the effectiveness to enhance fluid mixing inside a Y-shaped microchannel by manipulating convective EKI waves. The dependence of the critical voltage of applied static electric field to trig EKI to generate convective EKI waves on the conductivity ratio of the two adjacent streams was quantified at first. The effect of the strength of the applied static electric field on the evolution of the convective EKI waves and fluid mixing process were assessed in terms of scalar concentration fields, shedding frequency of the convective EKI waves and scalar mixing efficiency. The effectiveness of manipulating the convective EKI waves by introducing alternative electric perturbations to the applied static electric fields was also explored for the further enhancement of the fluid mixing process inside the Y-shaped microchannel.
New Type Hydroelectric Units to Coexist With Natural Ecosystem
Authors: Inagaki Akira , Tanaka Daisuke , Kanemoto Toshiaki
Published: March 2009

To prevent the warming global environment, the hydropower should occupy the attention of the electric power generation systems as clean and cool energy sources with the highest density. For the next leap in the hydroelectric power developments, however, we are under obligations to conserve natural ecosystems and/or to coexist with natures. To meet such circumstances, this paper proposes two kinds of the new type hydroelectric unit applicable to tidal currents, mountain torrents, rivers and/or water drain systems, and discusses the characteristics of the model turbine/unit.
Lagrangian Motion of Slightly Buoyant Droplets and Fluid Particles in Isotropic Turbulence
Authors: Gopalan Balaji , Malkiel Edwin , Katz Joseph
Published: March 2009

The diffusion of slightly buoyant diesel oil droplets in isotropic turbulence is studied using high speed in-line digital holographic cinematography. Diesel fuel droplets with specific gravity 0.85 are injected into a 50×50×70 mm3 sample volume located at the central portion of a nearly isotropic turbulence facility. The turbulence in the sample volume is fully characterized using 2D PIV. Probability density functions of the Lagrangian droplet velocity are very close to a Gaussian distribution, which justifies the use of Taylor’s [1] model to calculate diffusion parameters. Similar to Friedman & Katz [2] data, our current results confirm that the mean rise velocity of diesel droplets becomes higher than the quiescent rise velocity at high turbulence levels. For most of the present droplet sizes and turbulence level, the rms of the horizontal droplet velocity fluctuations exceeds that of the horizontal fluid velocity fluctuations. The rms values of the vertical droplet velocity fluctuations are higher than those of the fluid only for the highest turbulence level. The droplet to fluid velocity rms ratio in both directions increases with turbulence level, but decreases with increasing droplet size. Assuming Fickian diffusion, Lagrangian auto-correlation functions of 22,000 droplet tracks are used for calculating the diffusion coefficient as functions of droplet size and turbulence level. Using all the data, we show that the diffusion coefficient scaled by quiescent rise velocity and the turbulence integral length scale is a monotonically increasing function of the turbulence level normalized by the droplet quiescent rise velocity.
New Treatment of Pressure Boundary Conditions for DSMC Method in Micro-Channel Flow Simulations
Authors: Ye J. J. , Yang J. , Zheng J. Y. , Li W. Z. , He S. Z. , Ma Y. B.
Published: March 2009

Using DSMC to simulate micro flows in micro-channels, the numerical treatment of boundary conditions is very important. In this paper, several previous numerical treatments of boundary conditions are discussed with their merits and demerits, and a new treatment method based on the assumption of certain pressure distribution in the cells for boundary conditions is proposed. As comparable validity tests, it is applied in the DSMC simulations for the Poiseuille micro flows in micro-channels with four types of classical pressure boundary conditions. The dimensionless velocity profiles are shown and compared with analytical solutions derived from the Navier-Stokes equations with slip boundary conditions. The pressure distributions along the centerline of the micro-channel with the different boundary conditions are presented, and the simulation solutions agree well with the slip analytical solutions. As the Knudsen number increased, a strong linearity of the pressure distribution can be evidently predicted by the new method. Compared with the inlet and outlet velocity distribution, it is shown that the new method has better efficiency than the previous methods in the convergence.
Flow Phenomena in a Highly-Loaded Single-Stage Axial-Flow Pump: Comparison of Experimental and Numerical Results
Authors: Benra Friedrich-Karl , Dohmen Hans Josef , Schmidt Marina
Published: March 2009

In highly loaded axial flow pumps considerable changes of the flow behavior were reported when altering the flow rate from design point operation to part load operation. The flow structure which is changing from stable operating conditions to stalled flow conditions has been investigated in detail by Kosyna and Stark with experimental methods. The present paper focuses on the application of numerical methods to simulate the flow behavior in the pump which has been investigated experimental. The obtained numerical results using a commercial solver for the unsteady Reynolds averaged Navier-Stokes equations (URANS) have been compared to the experimental results of Kosyna and Stark et al. The characteristic of the pump at different operating points is compared to the measurement. The change in the flow structure at part load conditions which gives a decrease of head is reproduced by the simulation results. The vortex structure induced by the tip leakage flow is a flow phenomenon which is well-known in external aerodynamics and in axial-flow compressors at flow conditions close to stall. The change of this vortex structure at different operating conditions is shown. Also the part load recirculation vortex dominating the rotor tip flow at deep stall conditions as well as the cross passage vortex is visualized from the numerical results. All addressed flow phenomena are shown in contrast to the findings of the experimental investigations. This comparison of the flow fields for appropriate operating points shows that the reported change in the flow structure can be detected by numerical simulation as well.
Simulation of Rising Bubble With Conservative Level Set Method
Authors: Sˇtrubelj Luka , Tiselj Iztok
Published: March 2009

Conservative level set method, introduced by E. Olsson and G. Kreis in 2005 is discussed. The test case with rising bubble consists of spherical bubble of smaller density in stagnant liquid of higher density. Due to the buoyancy spherical bubble is rising up and changing its shape. After certain time the bubble reaches final velocity and final shape. An in-house code was used to perform the simulations. The final shape of the bubble was investigated and also build-up of the bubble rising velocity, starting from the rest exhibiting an overshoot before reaching its final asymptotic value. This test allows testing of numerical model which has to accurately take into account buoyancy, viscous stresses and surface tension effects.
An Uncertainty Analysis of the NIST Airspeed Standards
Authors: Yeh T. T. , Hall J. M.
Published: March 2009

The National Institute of Standards and Technology (NIST) provides calibration services for airspeed instrumentation. This document describes the uncertainty of the NIST airspeed standards. An extensive component analysis of the system was performed. The standard for airspeed measurement at NIST is a fiber optic Laser Doppler Anemometer (LDA), which is calibrated with known velocities produced by a rotating disk. Airspeed calibrations are performed in a wind tunnel which has a test cross section of 1.5 m by 2.1 m over a range of speeds from 0.15 m/s to 40 m/s. Over this range, the airspeed uncertainty is found to be a function of airspeed and the expanded uncertainty at 95% confidence level, i.e. k = 2, in m/s can be expressed by the root-sum-square of 0.0048V and 0.0068 m/s, where V is airspeed in m/s. This gives a maximum uncertainty of 4.6% at the lowest airspeed of 0.15 m/s and a minimum uncertainty of 0.48% at the highest speed of 40 m/s.
A Numerical Study of Size Segregation of Binary Mixtures in a Gas-Fluidised Bed
Authors: Zhang Sijun , Chen Baisong
Published: March 2009

This paper presents a numerical study of segregation of binary mixtures of particles in a gas fluidized bed (floatsam = 1 mm, jetsam = 2 mm in diameter). The well-mixed packing has been used as the initial condition in this simulation. Simulations are conducted under 3D conditions for particles with the application of the periodical boundary to the front and rear walls. The gas is injected uniformly at the bottom. Simulation are conducted with two different gas injection superficial velocities, one with 0.8 m/s, the other 1.2 m/s. Bed pressure drop has been recorded as a function of velocity and time. The results show that the degree of segregation is affected by gas velocity significantly, a clearly partial segregation occurs at gas injection velocity 0.8 m/s, while well mixed at 1.2 m/s. Mixing kinetics has been examined by use of the modified Lacey mixing index and explained in terms of microdynamic information.
Control of Self-Excited Oscillations in Centrifugal Blowers
Authors: Ahmed Saad A.
Published: March 2009

Centrifugal compressors or blowers are widely used in many industrial applications. However, the operation of such systems is limited at low-mass flow rates by self-excited flow instabilities which could result in rotating stall or surge of the compressor. These instabilities will limit the flow range in which the compressor or the blower can operate, and will also lower their performance and efficiency. Experimental techniques were used to investigate a model of radial vaneless diffuser at stall and stall-free operating conditions. The speed of the impeller was kept constant, while the mass flow rate was reduced gradually to study the steady and unsteady operating conditions of the compressor. Additional experiments were made to investigate the effects of reducing the exit flow area on the inception of stall. The results indicate that the instability in the diffuser was successfully delayed to a lower flow coefficient when throttle rings were attached to either one or both of the diffuser walls (i.e., to reduce the diffuser exit flow area). The results also showed that an increase of the blockage ratio improves the stability of the system (i.e., the critical mass flow rate could be reduced to 50% of its value without blockage). The results indicate that the throttle rings could be an effective method to control stall in radial diffusers.
Turbulent Flow Over Cavities in an Asymmetric Diverging Channel
Authors: Shah M. K. , Tachie M. F.
Published: March 2009

An experimental investigation of turbulent flow over a single cavity in an asymmetric diverging channel is presented. Cavities of two different aspect ratios, w/h = 1 and 4, of height h = 6 mm were studied. The Reynolds number based on the approach freestream velocity and cavity height was Reh = 5000. Particle image velocimetry technique (PIV) was used to conduct detailed velocity measurements upstream of the cavity, inside the cavity and as far downstream of the cavity as x/h = 50. Mean velocity, turbulent intensities and Reynolds shear stress were obtained to document the effect of the cavity on the flow in the presence of adverse pressure gradient.
Active Aerodynamic Load Control of Wind Turbine Blades
Authors: Berg Dale E. , Zayas Jose R. , Lobitz Donald W. , van Dam C. P. , Chow Raymond , Baker Jonathon P.
Published: March 2009

The cost of wind-generated electricity can be reduced by mitigating fatigue loads acting on the rotor blades of wind turbines. One way to accomplish this is with active aerodynamic load control devices that supplement the load control obtainable with current full-span pitch control. Thin airfoil theory suggests that such devices will be more effective if they are located near the blade trailing edge. While considerable effort in Europe is concentrating on the capability of conventional trailing edge flaps to control these loads, our effort is concentrating on very small devices, called microtabs, that produce similar effects. This paper discusses the work we have done on microtabs, including a recent simulation that illustrates the large impact these small devices can exert on a blade. Although microtabs show promise for this application, significant challenges must be overcome before they can be demonstrated to be a viable, cost-effective technology.
Flow Visualization of Liquid/Liquid Optical Waveguide Microfluidic Device
Authors: Sugii Yasuhiko , Ishikawa Yasutaka
Published: March 2009

A liquid/liquid optical waveguide microfluidic device made of PDMS (polydimethylsiloxane) was developed in order to investigate chemical reaction and mass-transfer such as extraction, adsorption, mixing and diffusion at the liquid/liquid interface. In the micro scale, since the scale effect that the gravity force can be negligible and flow become laminar was appeared, a stable liquid / liquid sheath flow can be generated. In order to investigate the flow field concentration distributions of molecule in the present microfluidic device were measured using micro LIF (laser induced fluorescence) technique. The measurement results show the stable and long interface of miscible liquid flow.
The Algorithm on Multi-Secondary Controlling Acoustic Sources for Instabilities and Noise of Combustion
Authors: Dong Fei , He Guoqiang , Zhang Guitian
Published: March 2009

The algorithm on secondary controlling sound sources intension and their controlling effect is theoretically investigated in unstable combustion. Firstly, the equations of sound wave are deduced and the items of source are simplified. Then, the formulations on secondary controlling sources intension and controlling result are introduced according to the criteria making sound potential energy of combustor minimized and a detailed simple example followed.
Consideration of Course Improvement Activities and Its Effect on Mechanical Designing and Drawing Project
Authors: Uneda Michio , Fujiki Nobuaki
Published: March 2009

The Department of Mechanical Engineering at Kanazawa Institute of Technology has offered a creative mechanical designing and drawing subject, entitled “Machine Design Project (MDP)”, to third year students. It is well known that it is difficult to perform a scholastic evaluation for a creative subject. Moreover, the instructors’ loads are large owing to the large quantity of reports from students. In such a background, we have carried out course improvement activities of the MDP from 2005. The improvement activities and its effects and problems are examined, and the considerations based on the questionnaire results are reported in this paper.
Determination of Heat and Mass Transfer Coefficients by Condensation in an Air Cooler
Authors: Esfandiari Nia Fatemeh , van Paassen Dolf
Published: March 2009

This paper describes an improved class of heat and mass transfer air cooler model. The model is based on the approach of Green [1]. It delivers a compact and fast model that is appropriate for year round simulations of air conditioning systems. The model is validated through a set of experiments in the laboratory with an air cooler of eight rows. The heat transfer coefficients have been derived from the standard relations. For a good agreement between the measurements of a wet cooler and the model solutions, a substantial correction in the heat transfer coefficients is needed. In addition, the results obtained from the measurements indicated that the heat transfer coefficient itself and the correlation between heat and mass transfer had to be adapted. Acceptable results were obtained when mass transfer coefficient was adjusted by a correction factor. The decrease in heat transfer has been observed with an increase in dehumidification and the same could be concluded from the coupling of heat and mass transfer. The fins are not completely wet, which implies that an analogy between sensible and latent heat only partly exists. The model does not take wetness of the pipe into account. To overcome this problem, the Lewis number is modulated, based on the degree of dehumidification. In other words, the smaller mass transfer coefficient, there is the higher the dehumidification.
Experimental and Computational Analyses of Pressure Differentials in Flexible Ducts With Different Bent Angles
Authors: Taghavi Ray R. , Jin Wonjin , Medina Mario A.
Published: March 2009

A set of experimental analyses was conducted to determine static pressure drops inside non-metallic flexible, spiral wire helix core ducts, with different bent angles. In addition, Computational Fluid Dynamics (CFD) solutions were performed and verified by comparing them to the experimental data. The CFD computations were carried out to produce more systematic pressure drop information through these complex-geometry ducts. The experimental setup was constructed according to ASHRAE Standard 120-1999. Five different bent angles (0, 30, 45, 60, and 90 degrees) were tested at relatively low flow rates (11 to 89 CFM). Also, two different bent radii and duct lengths were tested to study flexible duct geometrical effects on static pressure drops. FLUENT 6.2, using RANS based two equations - RNG k-ε model, was used for the CFD analyses. The experimental and CFD results showed that larger bent angles produced larger static pressure drops in the flexible ducts. CFD analysis data were found to be in relatively good agreement with the experimental results for all bent angle cases. However, the deviations became slightly larger at higher velocity regimes and at the longer test sections. Overall, static pressure drop for longer length cases were approximately 0.01in.H2O higher when compared to shorter cases because of the increase in resistance to the flow. Also, the CFD simulations captured more pronounced static pressure drops that were produced along the sharper turns. The stronger secondary flows, which resulted from higher and lower static pressure distributions in the outer and inner surfaces, respectively, contributed to these higher pressure drops.
Effect of Retention Time of Neutrophils in Alveolar Capillaries on Increase in Their Concentration in the Capillary Network
Authors: Shirai A. , Hayase T.
Published: March 2009

It is said that neutrophils, a kind of leukocytes, can be retained in pulmonary alveolar capillary bed, even in normal lungs, resulting in higher concentration than in systemic circulation due to their relatively low deformability, and the concentrated neutrophils help the lung to effectively eliminate the enemies invading from outer air. The authors have developed a model to simulate the flow of neutrophils through an alveolar capillary network, considering the cells’ low deformability as the dominant factor for the retention. Flow of a suspension of neutrophils in plasma through a simplified lattice alveolar capillary network model was numerically simulated to investigate the effect of the retention on the increase in the concentration ratio of the cells between in the network and in the suspension. The numerical result showed that the ratio was lower than the experimentally obtained value. Other possible factors to influence the cell’s retention time are friction and adhesion of the cell on the endothelium. In the last study, effect of the retention time of the cells in individual capillary segments on the increase in the concentration ratio was investigated to suggest the ratio may have an upper limit no matter how long the retention time is extended. In this paper, the authors investigated the contribution of various parameters which affect transit time of a neutrophil through a single capillary segment to the relationships between the retention time and the concentration ratio. Finally, it was shown that the number of cells in the network increased to approach a finite value as the increase in the coefficient, independent of the cell property, concentration of the cells in the suspension or the capillary shape. Transition of the relationship was changed with the parameters.
Hydrodynamic Problems in an Industry-Academia Cooperation Program
Authors: Furuya Okitsugu
Published: March 2009

In Japan it is a common practice that the student at the senior year in engineering education needs to conduct a thesis work as a part of the graduation requirement. In most cases he or she becomes a member of a specific research laboratory where the professor provides a thesis project for the student to complete within a year. Engineering Clinic Program (ECP) at the Kogakuin University (KU) is an industry-academia cooperation program where the company provides a project for the students who work together as a team of four to five. ECP replaces the traditional thesis work for the graduation requirement. All projects in ECP coming from the industry are of open-end and of most advanced technology so that the students work on the real world problems just like the engineer in the company. The technical liaison from the company together with the faculty advisor guides the students, although they never give the solution to them. They should come up with some solutions to the problem within the limited timeframe and thus the creative ability and also management capability are cultivated. The students learn how to apply the knowledge learned at class to solving a real engineering problem. The problems the industry provides to ECP are of wide variety and also multidisciplinary in the engineering field. Among them, presented herein are two fluid dynamic problems handled in ECP in the past,: 1) development of accurate droplet measurements in intravenous injection pump, and 2) study of a journal bearing for Jet Pump. How these fluid dynamic problems provided from the industry were handled by the students with the help of the liaisons and advisors are described in this paper.
Laboratory Measurement of Entrainment and Mixing in Oceanic Overflows
Authors: Chen Jun , Odier Philippe , Rivera Michael , Ecke Robert
Published: March 2009

The mixing and entrainment processes existing in oceanic overflows, e.g., Denmark Strait Overflow (DSO), affect the global thermohaline circulation. Owing to limited spatial resolution in global climate prediction simulations, the small-scale dynamics of oceanic mixing must be properly modeled. A series of experiments are performed in an Oceanic Overflow Facility to study the mixing and entrainment of a gravity current along an inclined plate, flowing into a steady ambient medium. At small values of the Richardson number, the shear dominates the stabilizing effect of the stratification and the flow at the interface of the current becomes unstable, resulting in turbulent mixing. In addition, the level of turbulence is enhanced by an active grid device. Using PIV and PLIF to measure, respectively, the velocity and density fields, we characterize the statistical properties of the mixing. We also study the entrainment of the ambient fluid by the flow. An accurate parametrization of the mixing and entrainment can be a valuable input for ocean circulation models.
Multi-Physics Simulation of Electro-Chemical Machining Process for Three-Dimensional Compressor Blade
Authors: Fujisawa Toshiaki , Inaba Kazuaki , Yamamoto Makoto , Kato Dai
Published: March 2009

Electro-Chemical Machining (ECM) is an advanced machining technology. It has been applied to highly specialized fields such as aerospace, aeronautics and medical industries. However, it still has some problems to be overcome. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are the typical ones. To solve such problems, CFD is expected to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict the flow has not been established because of the complex flow natures. In the present study, we develop a multi-physics model and a numerical procedure to predict an ECM process. They are verified to the canonical ECM process for a two-dimensional flat plate, and then applied to the ECM process for a three-dimensional compressor blade. It is exhibited that the present model and numerical procedure can satisfactorily predict the final shape of the blade. In addition, using the computed results, the multi-phase flow, thermal and electric fields between the tool and the blade are numerically investigated.
Dynamic Analysis of the Joined-Wing Configuration in High-Altitude Long-Endurance Aircraft Using Fluid-Structure Interaction Model
Authors: Ravindren Prabu Ganesh , Ghia Kirti , Ghia Urmila
Published: March 2009

Recent studies of the joined-wing configuration of the High Altitude Long Endurance (HALE) aircraft have been performed by analyzing the aerodynamic and structural behaviors separately. In the present work, a fluid-structure interaction (FSI) analysis is performed, where the fluid pressure on the wing, and the corresponding non-linear structural deformation, are analyzed simultaneously using a finite-element matrix which couples both fluid and structural solution vectors. An unsteady, viscous flow past the high-aspect ratio wing causes it to undergo large deflections, thus changing the domain shape at each time step. The finite element software ANSYS 11.0 is used for the structural analysis and CFX 11.0 is used for the fluid analysis. The structural mesh of the semi-monocoque joined-wing consists of finite elements to model the skin panel, ribs and spars. Appropriate mass and stress distributions are applied across the joined-wing structure [Kaloyanova et al. (2005)], which has been optimized in order to reduce global and local buckling. The fluid region is meshed with very high mesh density at the fluid-structure interface and where flow separation is predicted across the joint of the wing. The FSI module uses a sequentially-coupled finite element equation, where the main coupling matrix utilizes the direction of the normal vector defined for each pair of coincident fluid and structural element faces at the interface [ANSYS 11.0 Documentation]. The k-omega turbulence model captures the fine-scale turbulence effects in the flow. An angle of attack of 12°, at a Mach number of 0.6 [Rangarajan et al. (2003)], is used in the simulation. A 1-way FSI analysis has been performed to verify the proper transfer of loads across the fluid-structure interface. The CFX pressure results on the wing were transferred across the comparatively coarser mesh on the structural surface. A maximum deflection of 16 ft is found at the wing tip with a calculated lift coefficient of 1.35. The results have been compared with the previous study and have proven to be highly accurate. This will be taken as the first step for the 2-way simulation. The effect of a coupled 2-way FSI analysis on the HALE aircraft joined wing configuration will be shown. The structural deformation history will be presented, showing the displacement of the joined-wing, along the wing span over a period of aerodynamic loading. The fluid-structure interface meshing and the convergence at each time step, based on the quantities transferred across the interface will also be discussed.
Improvement in Numerical Prediction of Cavitating Flows Over Various 2D Geometries Using Modification to the Turbulence Model
Authors: Jayaprakash Arvind , Mahalatkar Kartikeya , Ghia Urmila , Ghia Karman
Published: March 2009

Cavitation often causes performance breakdown and damage. So, it is very essential to accurately predict and control this phenomenon. In the present study, the unsteady effects associated with cavitation are investigated for various geometries including a NACA 0015 hydrofoil, a convergent-divergent nozzle, and a wedge, using the flow solver FLUENT. The turbulent viscosity and/or the turbulence dissipation in the k-epsilon turbulence model are modified. The cavitation phenomenon is represented based on the full cavitation model developed by Singhal et al. (2002), and it considers the liquid-vapor mixture as a homogeneous fluid whose density varies with respect to the static pressure and whose mass fraction is known in advance. Also, this model takes into account the formation and collapse of the vapor bubbles. The k-epsilon model was originally developed for fully incompressible fluids, and does not account for highly compressible two-phase mixtures. Hence, it has been found to be unsatisfactory for predicting cavitating flow in presence of high compressibility in the vapor region. Coutier-Delgosha et al. (2001) attributed this to the over-prediction of eddy viscosity in regions of flow with high vapor concentration, and suggested a modification for the calculation of eddy viscosity. Though the modification works in capturing the dynamic behavior of the cavitation sheet, the accuracy of cavity length and frequency are not accurately predicted for high cavitation numbers. This is due to inability of Coutier-Delgosha’s turbulence modification to completely account for all the complex flow features present in the cavity closure region. Thus, a further modification based on geometry and cavitation type is introduced in the turbulence modification of Coutier-Delgosha. Better results were obtained for moderate cavitation numbers, but this modification failed to accurately predict the frequency of vapor-cloud shedding at high cavitation numbers. This discrepancy is attributed to the large (40000:1) variation of density in the liquid-vapor region. Hence, a new modification is suggested in the present work where the closure coefficients of dissipation production (C1epsilon) and dissipation (C2epsilon) in the turbulent dissipation equation are dynamically varied in the liquid-vapor region. A User-Defined Function (UDF) is implemented in FLUENT to achieve this dynamic variation of the above mentioned closure coefficients. This modification is being tested to predict the time-averaged cavity length and vapor-cloud shedding frequency of cavitating flow over a NACA 0015 airfoil. The poster will present comparisons of cavity length and vapor-cloud shedding frequency over a wide range of cavitation numbers as predicted by the present and previous turbulence modifications and those observed in experimental studies.
Preconditioned Density-Based Methods for All-Speed Flows
Authors: Zhang Sijun
Published: March 2009

A low Mach number preconditioning method has been implemented in commercial computational fluid dynamics software, CFD-FASTRAN. The preconditioning technique offers a way to formulate the Euler and Navier-Stokes equations such that convergences can be made independent of Mach number. This enhancement is shown to provide accurate steady/unsteady state solutions for transonic and low-speed flow through several test cases.
A MEMS-Based Shear Stress Sensor for High Temperature Applications
Authors: Tiliakos Nicholas , Papadopoulos George , O’Grady Andrew M. , Modi Vijay , Larger Ronan , Fre´chette Luc G.
Published: March 2009

Micro-electro-mechanical systems (MEMS) are an enabling technology that has lead to various miniature sensor concepts. Utilizing recent advances in silicon carbide (SiC) MEMS fabrication techniques allows for the development of a new series of sensors that leverages the high temperature capabilities of SiC. One such sensor concept is a shear stress sensor that can operate over a high dynamic range, and at very high temperatures, with an application emphasis on ground and flight testing in supersonic and hypersonic flow. The application of this fundamental sensor element and capacitance sensing design to very high temperature and very high shear environment, however, brings another set of challenges that involve the associated packaging and electrical control scheme. While this project is still a work in progress, we present an overview of our efforts to design, develop, fabricate and test a MEMS shear stress sensor for hypersonic aeropropulsion test and evaluation applications.
Slug Flow Evolution Along Horizontal Pipelines by the Two Fluid Model
Authors: Carneiro J. N. E. , Nieckele A. O.
Published: March 2009

At the present work a numerical analysis of the slug flow evolution along horizontal pipelines is performed, based on the Two-Fluid Model. For the statistically steady state regime, the slug characteristics, such as frequency, length and translational velocity are determined. An air and water two-phase fluid mixture is examined. The influence of the entrance liquid holdup is address. The frequency, translation velocity and length are compared with empirical correlations available in the literature with very good agreement.
Modified Reynolds Equation for Aerostatic Porous Radial Bearings With Quadratic Forchheimer Pressure-Flow Assumption
Authors: Nicoletti Rodrigo , Silveira Zilda C. , Purquerio Benedito M.
Published: March 2009

The mathematical modeling of aerostatic porous bearings, represented by the Reynolds equation, depends on the assumptions for the flow in the porous medium. One proposes a modified Reynolds equation based on the quadratic Forchheimer assumption, which can be used for both linear and quadratic conditions. Numerical results are compared to those obtained with the linear Darcy model. It is shown that, the non-dimensional parameter Φ, related to non-linear effects, strongly affects the bearing dynamic characteristics, but for values of Φ > 10, the results tend to those obtained with the linear model.
Development of High Durability Polymeric Bearing
Authors: Yeo Ching Biing , Ishida Takehisa , Okada Kanzo
Published: March 2009

A thin micro-motor has been developed comprising a molded polymeric rotor disk with cylindrical sleeve that functions as solid lubrication bearing. It is designed to overcome the frictional resistance and to provide vibration damping in the rotation. Accelerated ageing was conducted on this bearing system to assess the tribological endurance of plastic against surface wear. It was demonstrated that the wear resistance property of the plastic material can be significantly improved with Tetrahedral Amorphous Carbon coating for more than 1×109 continuous cycles. The experimental results provide indication of good reliability for using polymeric material in small rotational mechanism.
Effect of Axial Preloading and Wheel Offset on the Performances of Automotive Wheel Bearings
Authors: Li Gui-Hua , Huang Ping
Published: March 2009

With considering the contact angle variations, the nonlinear systems of equations are utilized to obtain load distributions of automotive wheel bearings with axial preloading under radial and lateral tire loads and analyze the effects of axial preloading and wheel offset on the performances of the bearings. The results show that the axial preloading has much more significant influences on the load distributions, the displacements, the system fatigue life and the moment rigidity than the wheel offset. The relative inclination angle is linearly proportional to the axial preloading. The moment rigidity and the system fatigue life are opposite to an amount of axial clearance. In order to improve the rigidity of the automotive wheel bearings and get longer service life synchronously, the bearings should be kept working at a negative axial clearance.
A Method for Determination of Elastohydrodynamic Behavior of Line Shafting Bearings in Their Environment
Authors: Andreau C. , Ferdi F. , Ville R. , Fillon M.
Published: March 2009

Safe operation of a rotating line shafting needs to use proper tools and methodology for an accurate determination of its static and steady state behavior in running conditions. Taking into account properly the characteristics of shaft environment is of primary importance. These characteristics are mainly bearing material behavior, oil film dynamic coefficients (stiffness and damping), flexibility and deformations of structure supporting line shafting bearings. Global non linear behavior of the entire system needs to be analyzed to get an accurate solution, as oil film dynamic coefficients depend on steady state location of shaft inside the considered bearing, which depends itself on oil film stiffness, and also on flexibility and deformations of supporting structure. Calculations of structure flexibility and deformations, as well as line shafting stiffness characteristics are performed straightforwardly using finite element method. Solving global matrix equilibrium equation needs to solve elastohydrodynamic (EHD) problem on each bearing. A specific finite element method is developed for this purpose. This method is attractive for taking into account thick and flexible bearing materials such as multi layer synthetic materials. It can also support further developments (effects of geometry defects on bearings, solving thermoelastohydrodynamic problem). The application of the method to the propulsion line shafting of a large LNGC ship (Liquid Natural Gas Carrier) is presented, the final target being the determination of the most optimum bearing offsets for operating safely the vessel in all relevant conditions.
Using Design of Experiments to Analyze the Connecting Rod Big-End Bearing Behavior
Authors: Francisco Arthur , Fatu Aurelian , Bonneau Dominique
Published: March 2009

The present work aims to identify the most influent factor in the behavior of a connecting rod big-end bearing. Supposing that the structure and the operating conditions are given, ten input parameters (oil properties, shells geometry, …) have been kept for this study. If the parameters can vary between a low and a high value, it would a priori require 210 Thermo-Elasto-HydroDynamic (TEHD) calculations. The use of Design Of Experiments (DOE) techniques will reduce this number to 25 insuring, nevertheless, the identification of the main factors.
Investigation of Friction Over a Wide Range of Normal Forces
Authors: Drees Dirk , Achanta Satish
Published: March 2009

Friction at different force, length, and time scales is of great interest in tribology. The mechanical, chemical, and physical (atomic) interactions, each operating at their own time length and force scale, makes friction complex. This work is an attempt to improve the understanding of friction at normal forces ranging from nN up to N. This investigation was carried out under reciprocating ball-on-flat sliding conditions on engineering surfaces like diamond-like carbon (DLC) and dual phase steel. The test equipments used for this investigation are an atomic force microscope, a microtribometer, and a macrofretting tester. It was observed that for a hard/hard tribocouple like DLC/Si3N4, the variation in the coefficient of friction is negligible whereas the variation is large when the tribocouple is hard / soft like in dual phase steel / Si3N4. By changing the surface roughness of the material, the dependence of friction on normal force could be altered or manipulated.
A Method for Determining the Non-Gaussian Probability Density Functions of Asperity Heights for Two Contact Surface Conditions
Authors: Liou Jeng Luen , Lin Jen Fin
Published: March 2009

Most statistical contact analyses assume that asperity height distributions (g(z*)) follow a Gaussian distribution. However, engineered surfaces are frequently the non-Gaussian with a character dependent upon the material and surface state being evaluated. When two rough surfaces experience contact deformations, the original topography of the surfaces varies with different loads. Two kinds of topographies are considered in the present study. The first kind of topography is obtained during the contact of two surfaces under a normal load. The second kind of topography is obtained from a rough contact surface after the end of the elastic recovery. The g(z*) profile is quite sharp and has a large value at its peak if it is obtained from the surface contacts under a normal load. The g(z*) profile defined for a contact surface after the elastic recovery is quite close to the g(z*) profile before contact deformations occur if the plasticity index is a small value. However, the g(z*) profile for the contact surface after the end of elastic recovery is closer to the g(z*) profile shown in the contacts under a normal load if a large plasticity index is assumed. Skewness (Sk) and kurtosis (Kt), which are the parameters in the probability density function, are affected by the change in the mean separation of two contact surfaces, or the initial skewness (the initial kurtosis is fixed in this study), or the plasticity index of the rough surface are also discussed on the basis of the topography models mentioned above.