bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation on the Flow Structure and Vortex Behavior at a Large Scale Pump Sump
Authors: Cong Guohui , Wang Fujun
Published: March 2009

Vortex in pump station sumps could lead to equipment operation with vibration and cavitations, and its impact is even stronger in large scale pump station sumps. In this study, the flow structure and vortex behavior in the sumps of a large scale pump station were investigated with a three dimensional CFD approach. The approach solves Reynolds averaged Navier-Stokes equations by the realizable k-ε turbulence model with wall function. The numerical simulations were carried out under three different water levels (low, standard and high) and three different pump operating combinations (operating with one, two or three pumps). The important flow feathers in the entire flow field such as submerged vortices, free-surface vortices were revealed. The strength and location of vortices under different operating conditions were presented. To reduce the vorticity magnitude in the sumps which would expand to affect the flow around pump inlet, effects of three different anti-vortex devices (DA, DB, and DC) for the pump station were also investigated numerically. It is found that the vortex attached to the floor has larger vorticity scale than that attached to side wall and back wall. The vorticity magnitude at higher sump water level is smaller than that at lower water level. The operation of multi pumps also has a strong impact to the flow patterns in sumps. Anti-vortex device DB has better performance than the two others, it decreases the floor attached and sidewall attached vortex and makes the pump inlet flow smooth.
Study on Operation Characteristics of Air Cushion Surge Chamber
Authors: Hu Jianyong , Zhang Jian , Zheng Yuan , Suo Lisheng
Published: March 2009

Air cushion surge chamber is a high performance device of water hammer protection and surge control. Its operation characteristics are important to long water distribution system. To operation simulation of air cushion surge chamber, polytropic equation method and rational heat transfer method are adopted presently. The former has not considered the heat transfer between gas and chamber wall. Though the latter considers this heat transfer, analysis of heat transfer type is improper. Gas characteristics of air cushion surge chamber in the processes of hydraulic transients in long distribution system are studied. This paper makes a deep analysis on rational heat transfer method in theory based on fundamental thermodynamic equations, and derives calculation equation of gas heat transfer with variable boundary through considering different air heat transfer types synthetically. Experiment is made in order to study on the polytropic exponent, more prefer value range of polytropic exponent is raised. So the new operation characteristics of air cushion surge chamber are obtained. Numerical calculation and model test results indicate that the new analysis method can simulate gas pressure variation more precisely in the process of hydraulic transients and ensure the safety of long water distribution system.
Study on the Operability Margin Variation of Butterfly Valve
Authors: Park Ju Yeop , Lee Gong Hee , Lee Do Hwan
Published: March 2009

Design basis capability of safety-related butterfly valve of nuclear power plant should be verified due to the regulation of Korea. Therefore, based on the results from the torque coefficient of thin symmetric plate, the nuclear utility has performed the engineering calculation to determine the required torque for operating a butterfly valve and the margin of operability at design basis condition. However, recent research showed that the torque coefficient of the thin symmetric plate used before is rather larger than newly determined one. Therefore, in the present study, the effect of change in the torque coefficient of thin symmetric plate on the operating margin is investigated. First, the recently determined valve loss coefficient of thin symmetric plate is modified at near valve full open position to reflect a finite thickness of valve disk. Second, the torque coefficient of symmetric disk butterfly valve is determined from the loss coefficient and the torque coefficient of thin symmetric plate and using this, the torque coefficient of butterfly valve with asymmetric disk is also deduced. Then, the variation on the hydrodynamic torque of butterfly valve is quantified and the operating margin variation of safety-related butterfly valve is determined. Calculations of the operating margin are performed for 10 butterfly valves of Uljin 6 nuclear power plant of Korea, which have all asymmetric valve disks. As expected, the hydrodynamic torque which is proportional to the torque coefficient is reduced and the resulting margin of operability is improved for opening safety direction. The margin improvement amounts to from 6.0% to 142.9% for valves considered. For closing safety direction, although the hydrodynamic torque is also reduced, the total dynamic torque due to overall hydrodynamic effect is increased from 1.1% to 63.0% on the contrary. This increase is because the hydrodynamic torque assists valve closing. Despite of these increases in the total dynamic torque, the operability margins of closing direction do not change at all. The reason is that the required torque for operating valve is determined not by the total dynamic torque but by the total seating torque which is more dominating. In conclusion, the margin improvement is significant for opening otherwise the margin deterioration is slight for closing when the torque coefficient is reduced.
Effects of Dynamic Surface Tension and Gas Permeation Resistance on the Stability of Microbubbles
Authors: Takahira Hiroyuki , Ito Daishi , Katsuyama Tomoaki
Published: March 2009

To understand the stability of microbubbles, the shrinkage and growth of microbubbles under variation of a pressure field are observed with a CCD camera. The influence of gas diffusion is investigated for two kinds of microbubbles; one is Levovist which is an air microbubble coated by palmitic acid, and the other is Imavist which is a PFC gas microbubble covered by lipid and surfactant. It is shown that when the ambient liquid pressure increases, a tiny microbubble shrinks accompanied with surface depression, and does not return to the initial size even after the pressure is reduced. On the other hand, a large microbubble shrinks nearly spherically. The depression of bubble surface suggests the formation of multilayers of surfactant or lipid on bubble surface. It is also shown that air diffusion enhances the growth of the Imavist. A bubble model is also constructed by considering dynamic surface tension and gas permeation resistance of surfactant or lipid layers. The previous experimental results in which a microbubble was trapped with a laser trapping technique are compared with simulations based on the model. The results show that the rate of adsorption of surfactant is much faster than the shrinking speed of microbubbles. The decrease of surface tension due to the decrease of the surface area of a microbubble is a significant factor to determine the bubble profile. Also, the present experimental results are compared with simulations. The simulations considering the gas permeation resistance are in good agreement with the experiments for nearly spherical bubbles. The results also show that the increase of the permeation resistance during bubble shrinkage stabilizes microbubbles.
Modelling Injector Flow Including Cavitation Effects for Diesel Applications
Authors: Ka¨rrholm F. Peng , Weller Henry , Nordin Niklas
Published: March 2009

In this paper, cavitation and pressure parameters measured in a model diesel injector are compared to data acquired by numerical simulations using a new code developed for the Open-FOAM platform, which uses a barotropic equation of state together with the homogeneous equilibrium assumption. It is a viscid code, allowing both compressible liquid and vapour to be modelled. The mass flow and cavitation probabilities obtained from the simulations are compared to data obtained in experiments performed at AVL’s laboratories, in which the flow through an almost two-dimensional nozzle was examined. The experimental data used include pressure profiles and cavitation images. The model proved to be able to predict cavitation probabilities, mass flows, and the occurrence of super-cavitation in the channel. In addition, it proved to be stable in its dependency on physical parameters, and grid independent.
Numerical Simulation of Two-Dimensional Free-Surface Flow and Wave Transformation Over Constant-Slope Bottom Topography
Authors: Dimakopoulos Aggelos S. , Dimas Athanassios A.
Published: March 2009

A numerical model is presented for the simulation of the two-dimensional, inviscid, free-surface flow developing by the propagation and breaking of water waves over a flat bottom of steep slope. The simulation is based on the numerical solution of the unsteady, two-dimensional, Euler equations subject to the fully-nonlinear free-surface boundary conditions, the non-penetration condition at the bottom and appropriate inflow and outflow conditions. A boundary-fitted transformation, which includes both the time-dependent free surface and the arbitrary bottom shape, is applied. For the numerical solution of the Euler equations, a two-stage fractional time-step method is employed for the temporal discretization, while a hybrid scheme is used for the spatial discretization. Finite differences are used in the streamwise direction and a pseudo-spectral method in the vertical direction. An absorption zone is placed at the outflow region in order to minimize wave reflection by the outflow boundary. Wave breaking is modeled by a surface roller breaking model, which modifies the dynamic free-surface condition. The simulation results are in very good agreement with available experimental results for the wave propagation and breaking over bottom with slope 1:35. Results, from the simulations over bottom with steeper slopes of 1:15 and 1:10, which generate strong spilling and mild plunging breakers, respectively, are also in very good agreement with available predictions for the breaking depth and wave height. In all cases, a vortex is formed under the breaking wave front and convected in the surf zone.
Study of Heat Transfer Characteristics in the Boundary Layer of a Visco-Elastic Fluid Under Varying Influencing Parameters
Authors: Anuradha P. , Krishnambal S.
Published: March 2009

The heat transfer characteristics of a visco-elastic fluid within the boundary layer formed by the passage of a sheet stretching at a uniform rate through it are studied under varying influencing parameters using a numerical technique. The influence of considering or ignoring elastic deformation in the thermal analysis is studied in the presence of chosen values of non-dimensional parameters like Prandtl number (Pr) and Eckert number (E). Two cases of sheet surface conditions are considered — (i) PST case involving prescribed surface temperature and (ii) PHF case involving prescribed heat flux at the surface. The results of this numerical study are diagrammatically represented with appropriate conclusions drawn on the influence of the above parameters considered in isolation or together. The trend of results is seen to agree well with those of other researchers who used other solution techniques. A judious choice of the above two principal non-dimensional parameters is suggested for application to a cooling process typical of a polymer extrusion industry.
Validation of a Dynamic Prescribed Vortex Wake Model for Horizontal Axis Wind Turbines
Authors: Currin Hugh D. , Coton Frank N.
Published: March 2009

A new aerodynamic wake model for Horizontal Axis Wind Turbines has been developed. The prescribed vortex wake code HAWTDAWG has been extended to dynamic flow and incorporated into AeroDyn. Linkage to the FAST structural dynamics code is retained. Static and dynamic yawed flow validation is done against Unsteady Aerodynamic Experiment Phase VI data as well as against existing code results.
Unsteady Characteristics of Turbulent Flow Over a Rectangular Cavity
Authors: Mori Takayuki , Naganuma Kenji
Published: March 2009

Unsteady characteristics of incompressible turbulent flow over a rectangular cavity were investigated with emphasis on its dominant frequency of oscillation and three dimensional features. Particle image velocimetry (PIV) measurements and fluctuating pressure measurements were carried out in a circulating water tunnel varying cavity length-depth ratio L/D=1 to 4 at Reθ=8,300. It is found that the dominant frequency of the fluctuation decreases with the increase of the cavity length and it exhibits broadband behavior instead of resonant one. The instantaneous flow field shows strong three dimensional distortions. Present results indicate that the spanwise distortion may weaken resonant interactions between shear layer and cavity trailing edge.
Almighty High Output Type Intelligent Wind Turbine Generator With Tandem Rotors
Authors: Kanemoto Toshiaki , Mitarai Hiromi , Kubo Koichi , Aoki Noboru , Esaki Nobuyuki , Maeyama Akinori , Eguchi Hidenori , Noda Hideharu , Yamada Ikumi
Published: March 2009

Wind is clean, renewable, and homegrown energy source of electric power generation, and has been positively/effectively utilized to cope with the warming global environment. The conventional turbines with large-sized wind rotor generate high output at moderate wind. The power generation of the small-sized wind rotor is low but is suitable for weak wind. That is, the size of the wind rotor must be correctly/appropriately selected in conformity with the wind circumstances. Moreover, the turbines must be equipped with the brake and/or the pitch control mechanisms, in general, to suppress the abnormal rotation and the generated overload at the stronger wind, and to keep good quality of the electric power. To overcome above weak points, the authors have invented the superior wind turbine generator, as shown in Fig. 1. This unit was called “Intelligent Wind Turbine Generator” by the authors, as the rotational speeds of the tandem wind rotors are adjusted pretty well in cooperation with the two armatures of the generator in response to the wind speed. This unit is composed of the large–sized wind rotor, the small-sized wind rotor and the peculiar generator with the inner and the outer armatures without the conventional stator. The front and the rear wind rotors drive the inner and the outer armatures respectively as shown in Fig.1. The rotational torque is counter balanced between the inner and the outer armatures of the generator. The rotational direction and the speed of both wind rotors/armatures are free, and automatically determined in response to the wind circumstance. The superior power generation of the proposed wind turbine generator was verified in the previous report. Continuously, this paper shows the effects of the front wind rotor profiles, the axial distance and the diameter ratio between both wind rotors on the turbine characteristics, in accompanying with the flow conditions around the tandem wind rotors-were experimentally investigated and shows the characteristics of the superior generator.
Performance Improvement of Vertical Pumps Using CFD
Authors: Chung Kyung-Nam , Kim Yang-Ik , Gong Hwan-Sik , Kim Sang-Chul
Published: March 2009

In this study performance of two vertical pumps has been improved by using CFD. The first pump is a vaporization sea-water pump which has 6 blade impeller and the specific speed of about 410. The second one is the cargo pump of a chemical product carrier. This pump is a submersible pump operating near the bottom of the cargo hold and has the specific speed of about 210. In order to get higher efficiency, the flow fields of the initial models of the pumps are simulated, and design directions are obtained by analyzing the flow fields. NPSH required values are also calculated to know whether the design models have good cavitation performance or not. Satisfactory results are obtained for the design models.
Computational Analysis of Characteristics and Mach Number Effects on Noise Emission From Ideally Expanded Highly Supersonic Free-Jet
Authors: Nonomura Taku , Fujii Kozo
Published: March 2009

In this study, aero-acoustic noise from super-sonic jet plume is computationally investigated. Three-dimensional Navier-Stokes equations are solved with seventh order weighted compact non-linear scheme and total validation diminishing Runge-Kutta time integration scheme. At first, the noise from Mach 2.0 ideally expanded super-sonic jet is computed and validated with the past experimental study. Then the noises from various Mach number (2.0–3.5) ideally expanded jet plumes are computed. Noise source positions, directivity and convective Mach numbers are discussed.
Internal Flow Characteristics of Cross-Flow Hydraulic Turbine With the Variation of Nozzle Shape
Authors: Choi Young-Do , Lim Jea-Ik , Kim You-Taek , Lee Young-Ho
Published: March 2009

The purpose of this study is to examine the optimum configuration of nozzle shape to further optimize the cross-flow hydraulic turbine structure and improve the performance. The results show that CFD analysis for the cross-flow turbine can be adopted as a useful method to examine the internal flow and turbine performance in detail. Pressure on the runner blade in Stage 1 and velocity at nozzle outlet have close relation to the turbine performance. The performance characteristics of cross-flow turbine have both impulse turbine and reaction turbine simultaneously.
Basic Study on Functional Fluid Pump
Authors: Tsukiji Tetsuhiro , Sato Hiroki , Suzuki Kenta
Published: March 2009

This study contributes to the development of a micro-pump in micro-fabricated systems. Our micro-pump uses the dielectrophoresis of a liquid to eliminate vibration-noise, and it requires little or no maintenance. Three-phase alternating currents are used as rotation electric fields to rotate the liquid crystal using the dielectrophoresis property. The pump has spiral flow channel and was designed based on the rotation mechanism of the liquid crystal by using the three-phase alternating currents. The relation between the maximum pressure and the shape of the flow channel in the pump was investigated for various electric fields. Furthermore, pressure-flow rate characteristics of the pump were measured. The maximum pressure increased when we used a liquid crystal with a high dielectric constant for the constant voltage. We developed a micro-pump using the dielectrophoresis of liquid crystals. The size of our pump can be decreased by further research.
Experimental Analysis of the Wind Farm and Numerical Site Calibration
Authors: Kamio T. , Iida M. , Arakawa C.
Published: March 2009

This paper mentions the difference of estimation methods for the Weibull distribution using the wind data that were measured at more than 300 locations to clarify the wind characteristics in a complex terrain. As the result, the Weibull distribution function is approximated the experimental wind data by the non-linear fitting method rather than the linear fitting method. Then the numerical site calibration with MASCOT which is the non-linear numerical wind prediction model and WaSP are run out on a complex terrain in Japan.
Rotor-Stator Interaction Induced Pressure Fluctuations: CFD and Hydroacoustic Simulations in the Stationary Components of a Multistage Centrifugal Pump
Authors: Berten Stefan , Dupont Philippe , Farhat Mohamed , Avellan Francois
Published: March 2009

In a centrifugal pump the interaction between the rotating impeller pressure field and the stationary diffuser pressure field yields pressure fluctuations as the result of a modulation process. These fluctuations may induce hydroacoustic pressure fluctuations in the exit chamber of the pump and could cause unacceptable vibrations. This paper presents a methodology for the prediction of hydroacoustic pressure fluctuations resulting from rotor-stator interaction in a multistage centrifugal pump. The method consists in the one-way coupling of incompressible CFD and hydroacoustic simulations. In a first step the rotorstator pressure fluctuations are calculated using a commercial 3D-RANS CFD-code (CFX 10) for different flow rates. The acoustic simulations are performed in two consecutive steps. Initially a free oscillation analysis using white noise pressure fluctuations is performed, which provides hydroacoustic eigen frequencies and mode shapes of the outlet casing. In a second step the spatially distributed pressure fluctuations from the CFD simulation are used to perform a forced oscillation analysis. This approach allows the prediction of possible standing waves in the hydraulic collection elements in the last stage of multistage pumps.
Nacelle Anemometry for the Electric Power Prediction System
Authors: Kuroda J. , Iida M. , Arakawa C.
Published: March 2009

The purpose of this study is to establish the nacelle anemometry for the wind forecast. This paper describes the problems of the meteorological anemometry and the nacelle anemometry based on measurement data in Japan. In the results, it is shown that wind velocity measured at the mast is less related with power output of wind turbines than measured at the nacelle. However it seems power curve referred to the nacelle anemometer to shift to lower wind velocity. Then the numerical simulation is carried out for the flow field around the nacelle and the blade as the first step.
The Measurement of Concentrated Flow Resistances in Periodically Operating Fluid Power Systems
Authors: Manhartsgruber Bernhard
Published: March 2009

Fluid power technologies have been applied for common rail fuel injection systems with great success over the last years. Another emerging application area can be found also in the automotive industry: The electro-hydraulic variable valve train system. Both applications share the problem of a hydraulic pressure rail under periodic excitation by the flow rates consumed either by common rail injectors or by the hydraulic valve drives. This excitation results in pressure oscillations in the desired constant pressure rails. For the modelling of these wave propagation phenomena, the availability of mathematical models for the dynamic influence of concentrated flow resistances like T-branches and sharp elbow bends is crucial. While there is abundant literature for the stationary flow case, the available experimental results for pulsatile flow or arbitrary periodic flow conditions are very limited. This paper describes a first experiment for the measurement of concentrated flow resistances in a rail system of straight bores with a circular cross section and a diameter of 10 mm. The test fluid is mineral oil and excitation frequencies are in the range of 10 to 1000 Hz.
Analysis of Numerical Simulation on Near Surface Beneath Clean and Contaminated Small-Scale Wind-Driven Water Waves
Authors: Hu Xiaoxia , Dolatabadi Ali , Siddiqul Kamran
Published: March 2009

We report on a numerical study conducted to investigate the near-surface flow beneath clean and contaminated small-scale wind-driven water surfaces. The numerical model is validated in terms of the velocity and surface wave characteristics. A good agreement is observed between the experimental and numerical values. The results from the numerical model show that the mean velocity in the near-surface region is 25–50% higher beneath the contaminated surface as compared to the clear surface. The present trend is also in agreement with the previous experimental observations.
Numerical Investigation of a Heated Sodium Jet in a Co-Flow
Authors: Otic´ I. , Class A. G.
Published: March 2009

Results of a numerical simulation of turbulent heated sodium jet in a co-flow using a combined LES-DNS approach are presented. The calculations correspond to the experiment of Knebel, Krebs, Muller and Axcell [1]. In agreement with the experimental results co-flow suppresses flow reversal along the outlet pipe wall. Comparisons of mean velocity, mean temperature, and temperature variance between experimental and numerical results show fairly good agreement. The results support the applicability of the combined LES-DNS approach for this type of flows. Simulations using this approach may complement experimental studies, allowing for better insight into the physical mechanisms of liquid metal turbulent heat transfer.
Large Eddy Simulation of Turbulent Heat Transfer Around a Circular Cylinder in Crossflow
Authors: Kim Sung-Eun , Nakamura Hajime
Published: March 2009

Large eddy simulation has been carried out of turbulent flow and heat transfer around a circular cylinder in crossflow at three subcritical Reynolds numbers (Re = 3,900, 10,000, 18,900) where the flow and heat transfer characteristics change rapidly with the Reynolds number. The computations were carried out using a second-order-accurate finite-volume Navier-Stokes solver that permits use of arbitrary unstructured meshes. A fully implicit, non-iterative fractional-step method was employed to advance the solution in time. The subgrid-scale (SGS) turbulent stresses and heat fluxes were modeled using the dynamic Smagorinsky model. The LES predictions were found to be in good agreement with the experimental data of Hajime and Igarashi (2004). The salient features of turbulent heat transfer in subcritical regime such as the laminar thermal boundary layer and the rapid increase with Reynolds number both in the mean and the r.m.s. Nusselt number in the separated region are closely reproduced by the predictions. The numerical results confirmed that the heat transfer characteristics are closely correlated with the structural change in the underlying flow with the Reynolds number.
Numerical Simulation of Free Surface Flows Using STACS-VOF Method
Authors: Srinivasan Vedanth , Wang De Ming
Published: March 2009

This paper presents a numerical method that couples the incompressible Navier-Stokes equations with the Volume of Fluid method in a Cartesian co-ordinate system for tracking immiscible interfaces in multiple dimensions. The governing equations are discretized based on a finite volume method on a non-staggered fixed grid. The free surface flow problem is solved as a single phase flow system in which the free surface is captured using a Switching Technique for Advection and Capturing of Surfaces (STACS) scheme. The effects of surface tension at the interfaces are treated using a Continuum Surface Force (CSF) model. The pressure velocity coupling is achieved using a SIMPLE strategy. The coupled system, implemented in the commercial CFD software, AVL FIRE/SWIFT, is applied to a two dimensional dam breaking problem. The simulation results reveal a multitude of phenomena such as, free surface vortex generation, air entrapment and splashing of the liquid surge front. The computational results are in good agreement with experimental data, wherever available. The effects of time and grid resolution on the solution behavior are elaborated in detail. Different convection schemes are tested and the current method is compared to another existing interface capturing methodology.
Three-Dimensional Structures in Experimental Density Currents
Authors: Firoozabadi B. , Afshin H. , Safaaee E.
Published: March 2009

Density currents are continuous currents which move down-slope due to the fact that their density is greater than that of ambient water. The density difference is caused by temperature differences, chemical elements, dissolved materials, or suspended sediment. Many researchers have studied the density current structures, their complexities and uncertainties. However, there is not a detailed 3-D turbulent density current data set perfectly. In this work, the structure of 3-dimensional salt solution density currents is investigated. A laboratory channel was used to study the flow resulting from the release of salt solution into freshwater over an inclined bed. The experiments were conducted with different bottom slopes, inlet concentrations and flow rates. In these tests, the instantaneous velocities are measured by an ADV apparatus (Acoustic Doppler Velocimeter). Results show that by increasing the bed-slope and inlet concentrations, the height of the current decreases. As the density current moves downward the channel or by increasing the discharge, the height of the density current increases. Finally, the effects of different variables such as the bed slope, concentration and flow rate of entering fluid on the velocity profile in different distances from the entrance is studied. The entrainment coefficient, lateral spreading and drag coefficient of the bed and shear layer between salt solution and ambient water is discussed.
Structure of Turbulence Around the Trailing Edge of a Rotor Blade
Authors: Soranna Francesco , Chow Yi-Chih , Uzol Oguz , Katz Joseph
Published: March 2009

This paper focuses on the structure of turbulence around the trailing edge of a rotor blade operating behind a row of Inlet Guide Vanes (IGVs) located upstream of the rotor. High resolution, two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. We focus on a small region around the rotor blade trailing edge, extending from 0.04c upstream of the trailing edge to about 0.1c downstream of it, c being the blade chord length. We examine the phase dependent distribution of turbulent kinetic energy (TKE) and its in-plane components of production rate. Impingement of an IGV wake on the suction surface of a rotor blade, near the trailing edge region, reduces the thickness of the boundary layer within the region impinged by the wake. The resulting increase in phase averaged shear strain rate increases the production rate and causes a striking increase in peak turbulent kinetic energy in the near wake. Streamwise velocity gradients, i.e. compression, also contribute to turbulence production, especially when the boundary layer at trailing edge is relatively thick, i.e. when it is not impinged by the IGV wake.
Control of Highly Loaded Airfoil Boundary Layer Separation
Authors: Lori Augusto , Ardebili Mahmoud , Andreopoulos Yiannis
Published: March 2009

Control of boundary layer separation has been investigated employing micro-actuated delta winglets. The flow with the array is simulated computationally on two-dimensional airfoil boundary layer. The simulations capture vortices formed by the impulsive motion of the delta wings. The vortices are part of recirculating zone in the wake of the actuator, which as they advect downstream, bring high momentum fluid into the near wall region of a separated flow. Preliminary results indicate micro-actuated delta wing array affect boundary layer separation favorably.
Fluid-Structure Interaction Simulation for Blood Vessel Using 3D Voxel Data Derived From Medical Image
Authors: Kumahata Kiyoshi , Watanabe Masahiro , Matsuzawa Teruo
Published: March 2009

We have used the voxel-based method to examine the Fluid-Structure Interaction (FSI) of blood flow and blood vessel wall. This method uses the voxel data that are Cartesian structured grid from medical image. We have confirmed the accuracy and reliability of this method for blood vessel. In this paper, we introduce backgrounds, kinetic models of blood vessel, a numerical method, and a result of experiment.
Investigation of Fundamental Transport Mechanism of Product Water From Cathode Catalyst Layer in PEMFCs
Authors: Owejan J. P. , Owejan J. E. , Tighe T. W. , Gu W. , Mathias M.
Published: March 2009

Understanding how water produced in the cathode catalyst layer is removed during PEMFC operation can be critical for materials optimization and representative models. The present work combines in-situ and ex-situ experiments to determine the dominant water discharge mechanism when considering capillarity and vapor transport. Water flux of vapor driven by the thermal gradient in the cathode diffusion layer is shown to be sufficient to remove product water at high current densities with saturated gas in the gas delivery channels. The role of an intermediate microporous layer and its impact in vapor versus liquid transport is also considered. Through novel experimental techniques and capturing all key physical interactions it is concluded that vapor diffusion is the fundamental mechanism by which water is removed from the cathode catalyst layer.
Coupling of Multiple High Speed Jets and Cavities
Authors: Panickar Praveen , Raman Ganesh
Published: March 2009

Configurations that exhibit fluid flow over twin open cavities occur fairly commonly in practical applications in the aircraft industry such as in weapons bays of modern aircraft and in landing gear wells of both commercial and military aircraft. This paper presents the results of ongoing research in the area of twin-cavity interaction using metrics from linear and nonlinear spectral analysis techniques and linear stability analysis. The primary goal of this paper is to document the similarities between interactions occurring in twin-cavities and twin-jets. Although the phenomenon of twin-jet interaction has been researched with a fair amount of thoroughness in the past, a study of twin-cavity interaction studies have not, thus far, been undertaken, to the best of the authors’ knowledge. During the course of this study, it was found that there were marked similarities between the phenomena observed in twin-jets and twin-cavities. In particular it was found that characteristics of twin-cavity interactions such as (i), unpredictable mode switching, (ii). nonlinear interactions acting as precursors to mode switching, (iii). Difference interactions in the cross-bicoherence spectra outnumbering the sum interactions, and (iv). nonlinear metrics showing an increase in the interactions between twin-cavities when linear metrics show a decay in the interactions, were common to both twin-jets and twin-cavities.
Experimental Study of Turbulent Cross-Flow Over Two Circular Cylinders Adjacent to Wall and Free Surface Boundaries
Authors: Paul S. S. , Tachie M. F. , Ormiston S. J.
Published: March 2009

A particle image velocimetry technique was used to study fluid flow around two identical circular cylinders arranged side-by-side with a fixed center-to-center distance. The vertical location of the cylinder pair was varied. The cylinders spanned the tunnel test-section and were oriented normal to the streamwise direction. The Reynolds number based on the cylinder diameter and the approach velocity was 2030. The mean velocity, turbulence intensities, Reynolds shear stress, and momentum flux distributions are used to study the influence on the flow of the free surface at the top of the tunnel and the wall at the bottom of the tunnel.
Modeling of Flow Acceleration Around Wind Farms
Authors: Moriarty Patrick , Kogaki Tetsuya
Published: March 2009

Recent measurements from operating wind farms demonstrate that the layout of the farm and interactions between turbine wakes strongly affects the overall efficiency of the wind farm. In some wind farms arranged in rectangular layouts, winds coming from the direction of the rectangular corner create a potential acceleration around the wind farm. This acceleration inherently leads to stronger local wind speeds at wind turbines downstream of the corner turbine, thereby increasing the power output of the downstream turbines. In this study, computational models are developed to predict this complex behavior seen in wind farms. The model used to examine these effects is a fully three-dimensional unsteady incompressible Navier-Stokes code, with the turbulence model turned off. Preliminary results show an optimum spacing configuration is possible. However, the results have yet to be verified at higher Reynolds number, which will be the effort of future work. Ultimately, these tools may lead to more optimal wind farm layouts.
An Experimental Investigation of the Flowfield and Dust Resuspension Due to Idealized Human Walking: Disk Model
Authors: Kubota Yoshihiro , Hall Joseph W. , Higuchi Hiroshi
Published: March 2009

To better understand how human movement causes particles to be resuspended from the ground, we performed flow visualization and PIV measurements on idealized human walking, a disk moved normal to the ground. The flow visualization indicates that particles are resuspended on both the down step and the up step of the walking process by a purely aerodynamic mechanism. The results suggest that a wall jet formed beneath the disk is responsible for particle resuspension, whereas large scale vortices created in the wake of the disk are responsible for the rapid redistribution of the resuspended particles.
PIV Investigation of an Open Channel Flow Over a Forward Facing Step
Authors: Shah M. K. , Tachie M. F.
Published: March 2009

The characteristics of an open channel turbulent flow over a forward facing step (FFS) are investigated in the present study. Two step heights, h = 6 and 9 mm, at Reynolds number, Reh, (based on the approach freestream velocity, U0, and step height, h) of 1900 and 2800 respectively were studied. Particle image velocimetry technique (PIV) was used to obtain detailed velocity measurements upstream of the FFS, in the reattachment region (x/h = 0, 1, 2) and in the redevelopment region (x/h = 4, 10, 15 and 50). The boundary layer integral parameters, mean velocity profiles and Reynolds stresses obtained in the reattachment and redevelopment region are used to document some of the salient features of the flow.
Modeling of Multi-Phase Flow in Electro-Chemical Machining: One-Way Coupling Versus Two-Way Coupling
Authors: Tsuboi Ryo , 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 issues. To solve such problems, CFD is considered to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict ECM process has not been established because of the complex flow natures. In the present study, we investigate the modeling of the two-phase flow (i.e. fluid and hydrogen bubbles) in ECM process. First, we present two models to calculate flow fields in ECM process. One is based on one-way coupling method, neglecting the effect from gas-phase to liquid-phase. The other takes account of the interaction between gas and liquid phases, namely two-way coupling method. In the later method, assuming that electrolyte and hydrogen bubbles have same velocity, we simplified the governing equations with Low Mach number approximation. We simulated ECM process for a flat plate channel configuration. And, we verified the present models by comparing the numerical result with the experimental data.
Numerical Study on Securing Evacuation Environment Under Fire at an Inclined Tunnel Part
Authors: Shingai Masashi , Iida Akiyoshi , Mizuno Akisato
Published: March 2009

We have experienced severe fire accidents in tunnels, such as in the Mont Blanc Tunnel or Tauern Tunnel. These accidents triggered a series of studies for securing safe environments in case of tunnel fire. Plenty of research has been done so far, experimentally or numerically, on the phenomena of tunnel fire, and the behavior of smoke and heat has been discussed for the flat part of the tunnel. At the inclined part, however, the analysis is not sufficient, and it is necessary to be studied. The authors estimated the behavior of heat and smoke by fire at an inclined tunnel part by means of a 3-D numerical analysis. The analysis was done utilizing a freeware, named “FrontFlow/red” developed by a group at Tokyo University. The simulation results give a detailed flow field as well as heat and smoke distribution, which can be used to establish tunnel facilities as ventilation systems and their control, so that safe environments can be attained. It is also available to decide the interval of cross passages for evacuation.
Influence of Design Parameters on the Unsteady Flow in a Centrifugal Fan
Authors: Younsi M. , Bakir F. , Kouidri S. , Rey R.
Published: March 2009

The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental study has been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these fans. The effects on the unsteady flow behavior related to irregular blade spacing, blade number and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using Computational Fluid Dynamics tools (CFD) based on Unsteady Reynolds Averaged Navier Stokes approach (URANS). The sliding mesh technique has been applied at the interfaces between the rotating and stationary zones in order to model the blades’ motion relative to the volute casing. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations (pressure and velocity fluctuations acquired upon the surfaces of the rotating blades) have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H). Using this model, the acoustic pressure has been computed at the fan exit duct. The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 [1] standard. In addition to this, pressure microphones have been flush-mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL) measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.
Steady-State Simulation of an Automotive Air Conditioning System Running on CO2
Authors: Morais Filho Pedro P. , Parise Jose´ Alberto R. , Marques da Silva Rui P.
Published: March 2009

This work presents a semi-empirical simulation of an automotive climate control system equipped with a transcritical vapor compression cycle running on carbon dioxide. The cycle components (a compressor, a throttling valve, an evaporator, a gas cooler, a suction accumulator and a suction line heat exchanger) were modeled to study the operation of the system, in the steady-state regime, under high ambient temperatures. The model took into account the severe conditions of tropical climates since the temperature at the inlet of the gas cooler is one of the predominant factors in the transcritical cycle performance. To assess the performance of the cycle, the thermodynamic model, reduced to a set of non-linear algebraic equations, was solved by a modified Newton-Raphson method. Reasonable agreement was found when results predicted by the model were compared with experimental data available in the literature.
A New Method for Numerical Prediction of Liquid Column Separation Accompanying Hydraulic Transients in Pipelines
Authors: Adamkowski Adam , Lewandowski Mariusz
Published: March 2009

The paper presents a new method for calculating pressure fluctuations in pipelines during a water hammer with liquid column separation. The method is based on the discrete-vapor-cavity model which assumes that vaporous cavities are formed in every computational section of the pipeline whenever the pressure drops to the vapor pressure at a given temperature. The method brings a significant improvement in prediction reliability as compared with the methods known so far. It eliminates disadvantages of basic methods used in practice — this is proved by comparisons between calculations made for several study cases. It is expected that the proposed method will become the main method in commercial codes used for simulating water hammer with the liquid column separation.
Mathematical Modeling of the Polymer Rotational Molding
Authors: Fomin Sergei A. , Kornev Konstantin G. , Wolter Chris , Young Jon , Brandenburg Tyler
Published: March 2009

We study the rimming flow of a viscoelastic film on the inner surface of a horizontal rotating cylinder. Simple lubrication theory is applied assuming that the Reynolds number is small and the liquid film is thin. For the steady-state flow of the Upper-Convected Maxwell (UCM) fluid the mathematical model reduces to a first order nonlinear ODE for the film thickness. We show that the liquid viscoelasticity changes the flow structure. In particular, the singularity observed for viscous liquids within the same lubrication approximation can be eliminated due liquid elasticity. We performed a detailed numeric analysis of the model and revealed some criticality regimes which are specific only for viscoelastic liquids.
Measurement of Liquid Flow Field Using Micro Bubbles Instead of Solid Particles
Authors: Minagawa Hisato , Yamada Satoshi , Terada Takashi
Published: March 2009

The authors have studied for the effect of supplying oxygen into water with micro bubbles produced by the shearing method, and found that the micro bubbles are very effective for the oxygen supplying compared with general size bubbles. We also generate micro bubbles which make water cloudy through the pressurizing dissolution method. The average diameter of micro bubbles generated with this method is about 40 micro meters in our laboratory. They are much smaller than those produced by the shearing method, and are the similar size to the tracer or the reflector used to measure the flow field by the PIV or the UVP (Ultrasonic Velocity Profile monitor). Moreover, they are very economical and ecological compared with solid tracer particles. Therefore, we examine to apply micro bubbles generated with the pressurizing dissolution method to the measurement of liquid flow field using the PIV or the UVP. A flow in a square cavity at Re = 1000 was measured using the PIV and the UVP. We could recognize a clear vortex. A flow around a circular cylinder was also measured using the PIV. We can recognize the possibility of micro bubbles for these applications.
Water Jet Effect on Solid Discharge in Siphon Tube
Authors: Shimizu F. , Shigefuji H. , Tanaka K. , Tokuda K.
Published: March 2009

The siphon phenomenon is widely used for the transportation system of water and it is very economical and ecological because the natural energy of water is only used for the power source of the transportation system. We consider that effective utilization of the siphon phenomenon is very useful for a discharge system of solid pills with water. In the present paper, the effects of water jet conditions and the flow tube configurations are experimentally investigated to enhance the discharge performance of the solid pills inside the water tank. From experimental results, it was clearly that an appearance of the siphon phenomenon enhanced the discharge performance of the solid pills from the water tank. And the influence of flow tube configurations appeared remarkably when the supply time of the water jet became long.