bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase-Stamp Particle-Trajectory Velocimetry Using Correlation Image Sensor
Authors: Kurihara Toru , Iwata Maoto , Ando Shigeru
Published: March 2009

In this paper, we propose a new measurement scheme, called phase-stamp particle trajectory velocimetry (PSPTV) using correlation image sensor (CIS). The correlation image sensor, developed by us, is the device which outputs the temporal correlation between incident light intensity and three reference signals which is common among whole pixel. By using the correlation image sensor with the single frequency reference signals, the time at which tracer particle is getting through is embedded in the form of the phase of the reference signals in each pixel. It provides single frame high resolution measurement of the 2D velocity field, and also good time resolution for transient phenomenon. We show some experimental results and confirmed its performance.
Large Eddy Simulation of a Gas-Turbine Combustor Using 2-Scalar Flamelet Approach
Authors: Nakashima Takuji , Oshima Nobuyuki
Published: March 2009

To investigate the ability of a numerical prediction method in a practical combustor system, we have conducted a numerical simulation of partially premixed turbulent combustion within a gas-turbine combustor geometry. A combination of Large-Eddy simulation and the 2-scalar flamelet approach are used to simulate unsteady turbulent combustion in modeling turbulent and combustion reaction phenomena and their interactions. With the successful simulation of both the premixed and non-premixed combustion states including the effects of turbulence, the predicted distributions of time-averaged temperature and the O2 mole fraction are found to essentially correspond to the experimental data. In an analysis of the predicted results, the weights of resolved and unresolved phenomena in the numerical prediction are estimated in order to discuss the effects of the turbulent combustion model applied to a practical combustion flow. The analysis determines the effect of turbulence on a Grid Scale that accelerates the premixed combustion reaction, while the modeled effect of turbulence caused by combustion acceleration as shown on a Sub-grid Scale is about twice of the effect as that seen on the Grid Scale.
Particle Dispersion in Fine Scales of Homogeneous Isotropic Turbulence
Authors: Sato M. , Tanahashi M. , Miyauchi T.
Published: March 2009

Direct numerical simulations of homogeneous isotropic turbulence laden with particles have been conducted to clarify the relationship between particle dispersion and coherent fine scale eddies in turbulence. Dispersion of 106 particles are analyzed for several particle Stokes numbers. The spatial distributions of particles depend on their Stokes number, and the Stokes number that causes preferential concentration of particles is closely related to the time scale of coherent fine scale eddies in turbulence. On the plane perpendicular to the rotating axes of fine scale eddies, number density of particle with particular Stokes number is low at the center of the fine scale eddy, and high in the regions with high energy dissipation rate around the eddy. The maximum number density can be observed at about 1.5 to 2.0 times the eddy radius on the major axis of the fine scale eddy.
Overset Grid Method for Large Eddy Simulation of Turbulent Flows Around Bluff Bodies
Authors: Itoh Y. , Tamura T.
Published: March 2009

The large eddy simulation of turbulent flow around a rectangular cylinder with side ratios of 1.0, 2.0, 2.67, and 3.0 at Re = 22000, is carried out using an overset grid system. In order to improve mass conservation along the boundary of computational domains, numerical procedures are proposed. The aerodynamic forces of rectangular cylinders can be predicted numerically. Details of pressure distributions along the side surface of the cylinder and turbulence structures in the wake is discussed, because there is a difference in accuracy of computational results in terms of the side ratio.
Fluid-Dynamic Force Characteristics of an Auto Rotating Flat Plate
Authors: Yasuda Takahiro
Published: March 2009

When a thin flat pate is released in still air, the plate automatically sets into a rotational motion. This phenomenon is called autorotation. The autorotating flat plate is loaded by unsteady fluid-dynamic forces. It is guessed that the forces are contributed by one due to vortex shedding from the edges of the plate and one due to the plate rotation, but the detail force characteristics have not been clear yet. In this study, we calculated the two types of flow by the discrete vortex method, one is flow around a rotating flat plate hinged about its center at constant rotating frequency in the uniform flow and the other is flow around a freely falling flat plate. The computed result in both types of flow agree well with the experiment. In the case of freely falling plate, autorotation phenomena could be predicted. By computed fluid dynamic forces, the contributions of vortex shedding from the plate to fluid dynamic forces and feedback effect of the fluid dynamic forces were found.
Analytic Solutions and Estimates for “C” in the Hydraulic Institute Equation for Reciprocating Pump Acceleration Pressure
Authors: Brunet Dexter
Published: March 2009

Acceleration pressure is an important factor in estimating the necessary boost pressure to prevent cavitation in reciprocating pumps. The Hydraulic Institute provides an equation for estimating acceleration pressure for crankshaft-driven reciprocating (CDR) pumps with piston centerline coincident with crankshaft centerline. This equation contains a numerical variable “C,” which is dependent on the number of cylinders in the pump and whether the pump is single acting or double acting. By means of the Maple™ [1] symbolic algebra computer program, this paper presents the following: • Analytic solutions for “C” for double-acting pumps with any odd number of cylinders and another analytic solution for pumps with any even number of cylinders. • General solutions for “C” that make the acceleration pressure equation analytic for pumps with 1 to 9 cylinders. • Estimated solutions for “C” for pumps with any numbers of cylinders greater than or equal to 3. The analytic solutions demonstrate that “C” is dependent on the connecting rod length, the crank throw radius, the effective diameter of the push rod, and the diameter of the piston.
Numerical Modeling for Flow and Transport in a Micro-Channel Fuel Cell Reformer
Authors: Yang Ru , Lin S. Y.
Published: March 2009

The flow and performance for a micro-channel reformer of a fuel cell is studied numerically. Methanol with water flows into a micro-channel with catalyst layer and is reformed to provide hydrogen for the fuel cell. The channel length is varied from 800 to 6000 μm and the channel height varied from 50 to 400 μm. The inlet flow velocity varies from 0.00001 to 0.002 m/s, and the inlet temperature varies from 250 to 350 °C. The density (area fraction on the wall) of catalyst varies from 25 to 100%. A reference case is chosen to have 100 μm channel height, 0.0001 m/s inlet velocity, and 100% catalyst density. The results indicate that the higher the inlet velocity, the lower the methanol conversion mass fraction. The variation of the conversion ratio is almost linear with the flow rate. As expected, the higher the catalyst desity, the higher the conversion effieciency. However, the present results indicate that the reduction of the catalyst density by a half only sacrifices 5% performance. In addition, the conversion efficiency decreases with the increase of the channel height, but increases with the increase of the inlet temperature. The present results can provide design reference for fuel cells with a micro-channel reformer.
Convective Cooling of an Extrudate
Authors: Huynh B. P.
Published: March 2009

Convective heat transfer about an isothermal, cylindrical extrudate of constant diameter, issuing continuously from an extrusion die, is investigated numerically, using a commercial CFD software package. The hot extrudate is assumed to move vertically downward, thus giving rise to a combined regime of forced and free convection in the surrounding fluid. Prandtl number of 0.707, corresponding to air near standard conditions, is used. It is seen that when extrudate speed is very low, heat transfer decreases as speed is increased. However this trend is reversed at higher extrudate speed. Flow pattern in the ambient fluid, and effects of Rayleigh number on the extrudate’s heat transfer, will also be presented.
Particle Size Classification Through Aerodynamic Jet Vectoring
Authors: Smith Barton L. , Humes Zachary E. , Minichiello Angela
Published: March 2009

An experimental and numerical demonstration of a new, non-contact particle sorting technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows to sharply turn a 2D, particle-laden jet. As the jet is turned, particles present in the flow experience a resultant force, dependent upon their size and due to the combined effects of pressure, inertia, and drag. Since the balance of these forces determines the particle’s trajectory, turning the flow leads to a separation of particles downstream. This simple, low-pressure-drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices. AVPS is experimentally demonstrated using a rectangular air jet. Particle size are measured using the Shadowgraphy method. Numerical simulations are performed using the commercial CFD solver FLUENT to calculate the 2D turbulent vectored jet flow field using a RANS approach. Examination of the mean and the standard deviation of measured and computed particle trajectories is used to determine the range of particle sizes that can be effectively sorted using AVPS. Our results indicate that while vectoring can be achieved with smaller control flow rates when blowing and suction are used together, fluctuations in the velocity field are much smaller when suction only is used. Furthermore, we have demonstrated that the jet flow can be vectored 90 with pure suction and 180 using a new geometry that allows for modification of the blowing angle on the fly. Using pure suction, particles from 10–40 micron and 2.5 times the density of water have been sorted to an accuracy of 1.5 micrometers. Sorting of heavy particles such as these is accomplished at very low speeds, reducing the tendency of damage to the particles. Lighter particles are sorted at higher speeds. Also using pure suction, particles from 5–40 μm and 0.6 times the density of water were sorted to an accuracy of 6.6 μm.
Suspension Spray in a Twin-Fluid Atomizer
Authors: Arabzadeh Sanaz , Dolatabadi Ali
Published: March 2009

Atomization of suspension solutions has a wide range of applications in many industrial processes. The application ranges from spray drug products, such as nasal spray and inhalation solution to spray drying, plasma spraying and coatings. In any atomization process the main spray characteristics are defined as drop size and velocity distributions, the spray path and the distribution of the liquid throughout the spray. These distributions are affected by several parameters including liquid and gas physical properties, nozzle geometry and operating conditions [1]. Thus understanding the behavior of gas and liquid flow through the nozzle is crucial to predict the thickness and momentum of the liquid flow at the outlet of the atomizer. In this work the Multi-Fluid Marker and Cell (MFMAC) technique is used to numerically model the structure of internal two-phase flow inside an aerated-liquid jet. The behavior of liquid film in the discharge passage was investigated using different Gas to Liquid mass Ratio (GLR) and these numerical results were compared with the available experimental data. This work was done as a baseline to validate the simulations and the effect of suspension solid particles on the structure of the two-phase flow at the exit cross section of the nozzle was also studied. The effect of concentration of solid particles on the performance of the atomizer is considered through change in the liquid bulk density and viscosity. By increasing in the amount of aerating gas, the liquid film formed in the discharge orifice, becomes thinner and the gas/liquid velocity ratio and momentum flux at the nozzle exit increases. It was found that the variation of solid particle concentration can have an influence on the internal flow characteristics such as the liquid thickness and the flow pattern inside the nozzle discharge passage.
Non-Uniform Velocity Distributions in Bipolar Plate PEM Electrolysis Cell
Authors: Nie Jianhu , Chen Yitung , Cohen Steve , Carter Blake , Boehm Robert F.
Published: March 2009

The rate of hydrogen production within the PEM electrolysis cell is influenced by the temperature, the velocity distributions, and the pressure distribution. In order to design and use a PEM electrolyzer cell effectively, analytical and/or numerical models for the device are necessary so that the system may be optimized. Numerical simulations of three-dimensional water flow were performed for the purpose of examining pressure and velocity distributions in the bipolar plate of a simplified PEM electrolysis cell. The flow range in the present study is assumed to be hydrodynamically stable and steady. The numerical results show that the pressure drops diagonally from the inlet tube to the exit tube. The velocity distribution is very non-uniform in the channels. A minimum of the peak values of mainstream velocity component in the channels develops in the middle of the plate. The maximum of these peak values appears in the channel near the exit tube. The lines along which the mainstream velocity component is a peak in the channel almost overlay with each other, except that a minor difference can be noticed in the channel near the exit tube.
LES and DNS of Turbulent Flows in Weakly Compressible Condition
Authors: Kajishima Takeo , Ohta Takashi
Published: March 2009

Flow field of low Mach number (e.g. M <0.3) is usually simulated by the incompressible flow scheme due to the severe limitation of time-increment in the compressible flow scheme. In this work, we propose a modification to the usual incompressible scheme, based on the elliptic equation for pressure, to improve the accuracy for turbulent flows considering weak compressibility. Two examples will be shown to validate our method. (1) LES (Large-Eddy Simulation) was conducted for turbulent flow around NACA0012 airfoil. Particular attention was focused on the influence of compressibility, despite the low Mach number range. In addition, new subgrid scale model of one-equation type using dynamic procedure was compared with traditional Smagorinsky model. Our method successfully reproduced the separation bubble near the leading edge, resulted in the improvement in the intensity of pressure fluctuation. (2) DNS (Direct Numerical Simulation) of turbulent flow in a plane channel is carried out, taking wall temperature difference into account. As a result of the density fluctuation in near-wall eddies, asymmetric profiles are observed in turbulence statistics. By the 4-quadrant analysis of turbulent shear stress, it is found that the ejection events in the vicinity of the walls are particularly affected by the density variation.
An Anisotropic Subgrid Model for Large Eddy Simulation of Wall Bounded Turbulent Flows
Authors: Badarayani Sachin S. , Squires Kyle D.
Published: March 2009

Large Eddy Simulation (LES) of high-Reynolds-number wall-bounded turbulent flows is prohibitively expensive if the energy-containing eddies in the near-wall region are resolved. This motivates the use of wall-layer models in which an approximate solution of the near wall dynamics is bridged to an LES of the outer flow. The main interest of the present work are wall-modeling strategies based on Detached Eddy Simulation (DES). In these approaches, the near-wall solution is closed using a Reynolds-averaged Navier Stokes model with a subgrid closure applied to the outer flow. As is well known, the original DES formulation applied directly as a wall model results in a shift in the velocity profile, corresponding to an under-estimation of the skin friction. A new formulation is proposed in this contribution in which the wall-parallel components of the modeled stress are reduced in order to lower the influence of the model and increase the resolved stress. The effectiveness of the new model is evaluated via comparison against DES predictions using the original and recently-proposed versions of the method. The effect of grid resolution and model parameters are also assessed using computations of turbulent channel flow at a Reynolds number based on friction velocity and channel halfwidth of 5000. The predictions show that the anisotropic form of the model stress yields an improved prediction of the mean velocity profile in better agreement with the logarithmic law and with larger resolved stress in the near-wall region.
Numerical Simulation of Dual-Jet System in Cross Flow
Authors: Kishore Aravind , Ghia Urmila , Ghia K. N.
Published: March 2009

Numerical simulations have been carried out for a dual-jet exhaust system issuing perpendicularly into a cross flow. The jets are of equal diameter, and the distance between the jets is four times the jet diameter, with effective velocity ratio of 5 for each jet. Visual evidence of the complex flow field developed is presented. The presence of a jet inside the region of influence of another jet is seen to produce coherent flow structures different from the structures seen in the single jet in cross flow configuration. It is observed that neither the jet center planes nor the plane mid-way between the jets act as symmetry planes. Hence, modeling multiple jets with the jet centre plane as a symmetry boundary may not be consistent with the physics involved. Results show that the dual-jet system does not penetrate into the cross flow as much as a single jet does. This behavior will significantly affect performance of multiple jet systems used for improved mixing.
Flow Stability in Pool-and-Weir Fishways, Plunging and Streaming Flows
Authors: Onitsuka Kouki , Akiyama Juichiro , Iiguni Yohei , Kiuchi Daisuke , Kawara Noriaki
Published: March 2009

In Japanese rivers, there are many river constructions, i.e., dams, weirs, drops, for the purpose of flood control. Fishways are river constructions which facilitate migration of fish past dams and weirs. There are a lot of fishway types such as pool-and-weir type, stream type, operation type and so on (see Nakamura, 1995). The pool-and-weir fishway is typical type in Japanese rivers. There are three types of flow regimes in pool-and-weir fishways such as a plunging flow, streaming flow and intermixed flow of plunging and streaming flows. Rajaratnam et al. (1988) proposed a prediction formula of these flow regimes. However, this formula has no physical meaning. Further the accuracy of formula is not high. In this study, the criterion formula, which can predict the flow regime in the pool-and-weir fishway, is suggested semi-theoretically. The experiments were conducted with changing the aspect ratio and discharge in the pool-and-weir fishway. The water surface profiles were measured with a point gauge and also two components velocities were measured with a 2-D electromagnetic current meter. A new criterion formula, which is able to predict the flow formation, is proposed.
Linear Stability of Sharp and Diffuse Interfaces Under Shear
Authors: Theofanous Theo , Sushchikh Svetlana , Nourgaliev Robert
Published: March 2009

We show that diffuse interfaces in shear flow are prone to instabilities that are of the same origin and character as the Yih-instability (for sharp interfaces between immiscible fluids). We also show that the development of these “Yih-like” instabilities towards “Yih” is monotonic, and that the agreement with Yih becomes quantitative as the limits of zero thickness and no-diffusion are approached.
Hyperbolicity, Discontinuities and Numerics of the Two-Fluid Model
Authors: Chang Chih-Hao , Sushchikh Svetlana , Nguyen Loc , Liou Meng-Sing , Theofanous Theo
Published: March 2009

The hyperbolicity boundaries of a (droplet) disperse, two-phase flow model at high flow speeds and relative velocities are found, the role of interfacial pressure on regularization is discussed, and the effects on integrability of the system of equations, solver robustness, and convergence properties are determined as a function of position relative to hyperbolic boundaries. We find good agreement between model and physics in that both exhibit a “sensitive” behavior in the transonic region (relative Mach number ∼1, hereafter omitting “relative” for brevity), and in that regularization requires increasing the interfacial pressure coefficient consistently with flow peculiarities in this region. The result is a two-phase flow model that is unconditionally hyperbolic and robust to grid refinement even in the most sensitive numerical tests with no dissipative terms in the equations.
The Relation Between Solidity and the Other Shape Factors for Complete Optimum Meridian Profile of Impeller With Guidevane
Authors: Tsugawa Takuji
Published: March 2009

In the previous paper, the solidity is independent shape factor of the optimum meridian profile by diffusion factor. But, the solidity is often calculated by the other shape factors, for example, the inlet and outlet flow angle, blade length, blade number and the co-ordinates of impeller meridian profile. So, in this paper, the solidity is treated as dependent shape factor and is calculated by the impeller meridian co-ordinates and flow angle. In the previous paper, the impeller meridian inlet is axial direction. In this paper, the inlet mixed flow angle of impeller inlet is one of additional shape factor. As the result, the impeller with guidevane complete meridian profile is calculated for the large diameter of guidevane outlet and the detailed meridian profile of impeller inlet.
Explicit Filtering LES for Turbulent Non-Premixed Combustion
Authors: Chakravorty Saugata , Mathew Joseph
Published: March 2009

Two models for large eddy simulation of turbulent reacting flow in homogeneous turbulence were studied. The sub-grid stress arising out of non-linearities of the Navier-Stokes equations were modeled using an explicit filtering approach. A filtered mass density function (FMDF) approach was used for closure of the sub-grid scalar fluctuations. A posteriori calculations, when compared with the results from the direct numerical simulation, indicate that the explicit filtering is adequate in representing the effect of sub-grid stress on the filtered velocity field in the absence of reaction. Discrepancies arise when reactions occur, but the FMDF approach suffices to account for sub-grid scale fluctuations of the reacting scalars, accurately.
Spectral Linear Stochastic Estimation of the Turbulent Velocity in a Square Three-Dimensional Wall Jet
Authors: Hall Joseph W. , Ewing Daniel
Published: March 2009

The instantaneous turbulent velocity field in a three-dimensional wall jet was estimated from the fluctuating wall pressure using a spectral Linear Stochastic Estimation (LSE) technique. The jet issued from a long square channel with Reynolds number of 90,000. Two downstream positions in the intermediate field were examined, x/h = 10 and x/h = 20, owing to the rapid change in wall jet development over this region. The results indicate that the passage of the large-scale structures causes large, coherent lateral sweeps of fluid across the entire span of the wall jet. The sweeps appear to be caused by the passage of half horseshoe-like structures. As the structures evolve downstream they develop a longer outer leg, and become more offset, traits that both contribute to the large lateral growth of this flow.
Deposition of Fine Solid Particles in Laminar Flat-Plate Boundary Layers
Authors: Hussainov M. , Kartushinsky A. , Michaelides E. E. , Rudi Y. , Shcheglov I. , Tisler S.
Published: March 2009

A method for the assessment of the deposition of fine solid particles in a vertical two-phase laminar flat-plate boundary layer is presented. The method is based on a probabilistic approach to the particles deposition and takes into account both the hydrodynamics of the flow past the plate and the adhesive properties of particles and the plate surface. Electrocorundum powders with particle sizes of 12, 23 and 32 μm were used for the investigations. A stainless steel hollow conical shape was used as a prototype surface for the particles deposition. The experimental investigation used the centrifugal technique for the deposition of particles and examined pairs of particles and surfaces for the characteristics of the deposition process. The results exhibited the typical log-normal distributions of the dependence of the deposition/adhesion process. An overall expression for the particles deposition flux was derived. The expression includes the normal to the surface velocity of the particles, the particle mass concentration observed immediately close to the surface of the plate and the surface of the plate. The hydrodynamic properties of the dispersed phase in the vicinity of the plate surface, namely the normal velocity and the particle mass concentration, were calculated by the mathematical model of the flat-plate laminar boundary layer elaborated in [1]. The validation of the proposed method of assessment of deposition was accomplished by comparing the deposition flux calculated along the plate with experimental data obtained in [2]. A small discrepancy between the numerical and experimental results was observed, which may be attributed to neglecting the microphysics of adhesion, such as the influence of the electric charges and humidity during the experiments.
Automatic Aerodynamic Design Through Evolutionary Techniques
Authors: Di´az Casa´s V. , Lopez Pen˜a F. , Duro R. J.
Published: March 2009

This paper is concerned with the presentation of an environment for automatic aerodynamic design. The approach followed in this environment involves three main elements: a search module based on evolution, a decoding module that allows a parametric definition of each solution, and an evaluation module which is based on an aerodynamic simulator. The search module seeks the best solution by means of macroevolutionary techniques and the evaluation module computes the efficiency of each individual by means of an aerodynamic simulator. This paper discusses the application of this environment to the aerodynamic design of wind turbine blades, ship hulls and sails.
Evolution of a Cavitating Bubble in a Nonuniform Pressure Field
Authors: Knyazev Vladimir A. , Soldatov Vladimir A. , Rohatgi Upendra Singh
Published: March 2009

The cavitation erosion problem is not a new one; however, it is still important and even becomes more pressing. This is associated with requirements to justify and extend service life of power-generating plants while obviously seeking the maximum efficiency. Currently semiempirical correlation relations are typically used in pump designing for prediction of modes of operation that may be hazardous in terms of development of cavitation erosion [1, 2]. It appears, however, that a progress can be made in this field by introducing numerical modeling of flow with direct modeling of the cavitation erosion process. This optimism is based on an established fact that the major effect of erosion damage is observed in the mode of operation between the “NPSH-incipient” mode (mode of activation of vapor-phase formation centers) and the “NPSH-3%” mode (mode where a noticeable vapor volume content is produced in the near-wall layer), i.e. in the mode of operation where the vapor volume content is small and its effect on flow characteristics can be neglected.
Numerical Simulations of Two-Dimensional Incompressible Flows Over Cavities and Their Control
Authors: Yoshida T. , Watanabe T.
Published: March 2009

We investigate numerically self-sustained oscillating flows over open cavities. The incompressible Navier-Stokes equations are solved using finite difference method for two-dimensional cavities with an upstream laminar boundary layer. A series of simulations are performed for a variety of cavity length to depth ratio. The results show mode switchings among nonoscillations, mode II and mode III oscillations. Variation of Strouhal number is in good agreement with available experimental data. The results of flow fields in the cavity reveal the relationship between the cavity shear layer oscillation modes and recirculating vortices in the cavity. We also demonstrate that oscillations are suppressed by our control method using moving bottom wall.
Numerical Modeling of Air-Grass Flow and BPF Noise in Lawn Mowers
Authors: Timushev Sergey , Gamarnik Alexandr , Tsipenko Anton
Published: March 2009

The noise of domestic machines including lawnmowers be comes an urgent issue. As the technology matures, designers need better tools to predict performance and efficiency of these machines across a wide range of operating conditions and find optimal ways to reduce noise. Computational fluid dynamics is an increasingly powerful tool which enables designer to better understand all features of unsteady flow in these machines and to find optimal designs providing higher energetic characteristics, better cutting quality and lower pressure pulsation, vibration and noise. Cutting quality linked with evacuation of grass is a key lawnmower characteristic. Due to this fact application of two-phase (air-grass) lawnmower flow model is inevitable in a prediction procedure. The modeling procedure comprises determination of lawnmower average aerodynamic characteristics and CFD-CAA analysis by acoustic-vortex method to predict sound power data. This method is based on splitting the equations of compressible fluid dynamics into two modes — vortex and acoustic Computational approach applied for the vortex mode flow is a “moving body”-technique: The problem is solved in the absolute frame of coordinates and computational grid changes during the blade passing. Computations can be made in 4 stages: 1) Computation of the incompressible medium with getting average values of energetic parameters; 2) Computation of the incompressible medium for definition the source function of inhomogeneous acoustic-vortex wave equation; 3) Solution of the acoustic-vortex wave equation; 4) Computation of 2-phase flow. In the 3rd stage the pressure pulsation field can be represented like a sum of acoustic and vortex oscillation. Wave equation is solved relatively to pressure oscillation using an explicit numerical procedure. Zero pulsatory pressure is an initial condition for solution of the wave equation. The local complex specific acoustic impedance is used to define boundary conditions for the acoustical part of the pressure field. Thus the numerical procedure gives pressure pulsations field and sound power data on blade passing frequencies (BPF). For the 4th stage computations effective grass particle parameters are determined with accounting the stubble effect on flow parameters and particularities of grass particle interaction with rigid surfaces. Results of a lawnmower air-grass flow (grass particle trajectories and concentration) and corresponding BPF sound power data prediction are presented as an example of modeling procedure application.
Effect of End Plates on the Performance of an Impulse Turbine for Wave Energy Conversion
Authors: Setoguchi Toshiaki , Takao Manabu , Kaneko Kenji , Nagata Shuichi , Toyota Kazutaka
Published: March 2009

The objective of this paper is to present the effect of end plate on the performances of the impulse turbine for wave energy conversion by experimental investigation. The experiments have been performed by model testing under steady flow conditions in the study. And then, the performances of the impulse turbine with end plates have been compared with those of the original impulse turbine, i.e., the impulse turbine without end plate. As a result, it is found that the characteristics of the impulse turbine with end plates are superior to those of the original impulse turbine. Furthermore, the effects of end plate size and penetration on the turbine characteristics have been clarified in the study.
Multi Objective Optimization of a Turbomachinery Blade Using NSGA-II
Authors: Samad Abdus , Kim Kwang-Yong , Lee Ki-Sang
Published: March 2009

This work presents numerical optimization for design of a blade stacking line of a low speed axial flow fan with a fast and elitist Non-Dominated Sorting of Genetic Algorithm (NSGA-II) of multi-objective optimization using three-dimensional Navier-Stokes analysis. Reynolds-averaged Navier-Stokes (RANS) equations with k-ε turbulence model are discretized with finite volume approximations and solved on unstructured grids. Regression analysis is performed to get second order polynomial response which is used to generate Pareto optimal front with help of NSGA-II and local search strategy with weighted sum approach to refine the result obtained by NSGA-II to get better Pareto optimal front. Four geometric variables related to spanwise distributions of sweep and lean of blade stacking line are chosen as design variables to find higher performed fan blade. The performance is measured in terms of the objectives; total efficiency, total pressure and torque. Hence the motive of the optimization is to enhance total efficiency and total pressure and to reduce torque.
Gas Bubble Formation in Stagnant and Flowing Mercury
Authors: Wendel Mark , Ibrahim Ashraf , Felde David , Riemer Bernard
Published: March 2009

The Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source (SNS) facility uses a liquid mercury target that flows through a stainless steel containment vessel. As the SNS pulsed beam power level is increased, it is expected that the target vessel lifetime could become limited by cavitation damage erosion (CDE). Bubbles produced in mercury at an upwards-oriented vertical gas injector needle were observed with proton radiography (pRad) at the Los Alamos Neutron Science Center (LANSCE). The comparison of volume-of-fluid (VOF) simulation results to the radiographic images reveals some aspects of success and some deficiencies in predicting these high surface tension, highly buoyant, and non-wetting fluid behavior. Although several gas flows were measured with pRad, this paper focuses on the case with a low gas flow rate of 1.66 mg/min (10 sccm) through the 0.2-mm-outer-diameter injector needle. The acoustic waves emitted due to the detachment of the bubble and during subsequent bubble oscillations were also recorded with a microphone, providing a precise measurement of the bubble sizes. When the mercury is also motivated coaxially, the drag on the bubble forces earlier detachment leading to smaller bubble sizes.
Experimental Investigation of Velocity Profiles in the Wake of an Oscillating Airfoil
Authors: Soltani M. R. , Mahmoudi M.
Published: March 2009

A series of experiments were carried out to study the unsteady wakes behind an oscillating airfoil. The airfoil is a section of a wind turbine blade oscillating in pitch about the quarter chord axis at various reduced frequencies, oscillation amplitude and mean angles of attack. Real time velocity profiles were obtained using total and static pressure at 35 vertically aligned points behind the airfoil via two similar rakes. The rakes were located at a distance of 1.5 chord length behind the model. The results show great influence of oscillation amplitude and reduced frequency on the wake velocity profiles.
Effects of Packing and Aspect Ratio on Mixing and Heterogeneous Catalysis in Microchannels
Authors: Bailey Robert T. , Ryan Stephen , Jones Frank , Wilson Stephanie , Hiestand James
Published: March 2009

Many industrial chemical processes involve the mixing of two or more liquids. By reducing chemical reactors to microscale dimensions, engineers seek to take advantage of decreased diffusion lengths, leading to increased effectiveness (e.g., higher purity of product) over larger process components. In this study, computational models developed using the commercial multiphysics code CFD-ACE+ are used to predict flow within microreactor channels. Two aqueous streams enter a channel—one containing a contaminant and the other devoid of the contaminant. Changes in two geometric attributes are investigated with respect to their effect on mixing of the streams: 1) packing feature layout within the channel and 2) channel aspect ratio. Reynolds numbers (Re) for the simulations range between 0.1 and 100. Results indicate that both packing feature position within the channel and channel aspect ratio can have a substantial impact on mixing. Between Re = 0.1 and Re = 1, mixing efficiency generally decreases with increasing Re; however, as the Re is increased from 1 to 100, fluid flow patterns in the channel are altered, and wake regions and streamline changes created by the packing features lead to improved mixing. Examples showing enhanced chemical conversion during heterogeneous catalysis as a result of better mixing are also presented.
A Microfluidic Model of Cardiovascular Bubble Lodging
Authors: Bull Joseph L. , Caldero´n Andre´s J. , Heo Yun Seok , Huh Dongeun , Futai Nobuyuki , Takayama Shuichi , Fowlkes J. Brian
Published: March 2009

Embolotherapy involves the occlusion of blood flow to tumors to treat a variety of cancers, including renal carcinoma and hepatocellular carcinoma. The accompanying liver cirrhosis makes the treatment of hepatocellular carcinoma by traditional methods difficult. Previous attempts at embolotherapy have used solid emboli. A major difficulty in embolotherapy is restricting delivery of the emboli to the tumor. We are developing a novel minimally invasive gas embolotherapy technique that uses gas bubbles rather than solid emboli. The bubbles originate as encapsulated liquid droplets that are small enough to pass through capillaries. The droplets can be selectively vaporized in vivo by focused high intensity ultrasound to form gas bubbles which are then sufficiently large to lodge in the tumor vasculature. We investigated the dynamics of bubble lodging in microfluidic model bifurcations made of poly(dimethylsiloxane) and in theoretical analyses. The results show that the critical driving pressure below which a bubble will lodge in a bifurcation is significantly less than the driving pressure required to dislodge it. Based these results, we estimate that gas bubbles from embolotherapy can lodge in vessels 20 μm or smaller in diameter, and conclude that bubbles may potentially be used to reduce blood flow to tumor microcirculation.
Current Status on High Performance Computing for Vehicle Aerodynamics Using Large Eddy Simulation
Authors: Tsubokura Makoto , Nakashima Takuji , Oshima Nobuyuki , Kitoh Kozo , Zhang Huilai , Onishi Keiji , Kobayashi Toshio
Published: March 2009

The world’s largest class unsteady turbulence simulations of flow around vehicles were conducted using Large Eddy Simulation (LES) on the Earth Simulator in Japan. The main objective of our study is to investigate the validity of LES, as an alternative to a conventional wind tunnel measurement or the Reynolds Averaged Navier-Stokes method, for the assessment of vehicle aerodynamics.
Image Analysis of Human Nailfold Capillary With High Speed Digital Video Capillaroscopy
Authors: Kuroda H. , Iribe M. , Matsubara M. , Watanabe M. , Sanada T.
Published: March 2009

Diagnoses of skin diseases are considerably difficult tasks due to the multiply-folded factors. Nailfold capillaroscopy has been developed to diagnosis microvascular disturbances mainly in connective tissue diseases, including systemic sclerosis, dermatomyositis, systemic lupus erythematosus, and Raynaud’s phenomenon. Capillaroscopy is non-invasive, easy to use, low cost and suitable for observation of these typical phenomena. We improved conventional capillaroscopy by constructing “high speed digital video capillaroscopy”, by integrating high speed digital video camera, deep-focus zoom lens, appropriate light source and light collecting adaptor. High speed digital video camera enabled us to observe the individual red blood cell in human nailfold capillary in vivo. The light collecting adaptor is effective for preventing skin from excessive light exposure, which causes serious damage. The first objective of this study is to extract the shape of nailfold capillary quantitatively by using binarization and the level-set method. By using the level-set method, the function, which distinguishes outside from inside of the capillary and also evaluates radius distribution along the capillary center line, is calculated. Based on this mathematical description of capillary shape, more rigorous definition of the capillary red blood cell velocity than the conventional method is obtained. The second objective of this study is to propose the innovative measurement method of red blood cell velocity in nailfold capillary. As plasma gaps show high brightness we trace them and estimate the velocities of blood cells on the center line of capillary. The last objective of this study is to observe the behavior of red blood cell. We evaluate the movement of individual red blood cell, not only in the axial direction but also the lateral direction. We analyze the series of images of red blood cells in capillary and discuss their behavior.
Numerical Aanalysis of a Leuko-Reducing Bowl for Intermittent Plateletpheresis System
Authors: Morinishi Youhei , Sakota Koichiro , Inaba Shoichi
Published: March 2009

Platelet therapy remains one of the most effective treatments. The use of WBC-depleted platelet is now mandatory to prevent a variety of adverse effects caused by transfused WBC (white blood cell) contaminating platelet. One of the current centrifuge bowls, which has most advantage for donors, has to use a WBC-depletion filter to meet the standards of WBC contamination. Development of new centrifuge bowls is intended here with the aid of CFD to guide the design of better performances. The simulation is in two stages; the first is to elucidate the mechanism of WBC-contamination of the current bowl (trajectory of WBC, based on velocity field established), and the second is to simulate the performance of new bowls on reducing remaining WBC in platelet concentrate. Evaluation of new bowls with human blood is reported.
Numerical Simulation of Nonlinear Water Wave Propagation Over Rippled Bed
Authors: Kolokythas Gerasimos A. , Dimas Athanassios A.
Published: March 2009

In the present study, numerical simulations of the free-surface flow, developing by the propagation of nonlinear water waves over a rippled bottom, are performed assuming that the corresponding flow is two-dimensional, incompressible and viscous. The simulations are based on the numerical solution of the Navier-Stokes equations subject to the fully-nonlinear free-surface boundary conditions and the suitable bottom, inflow and outflow boundary conditions. The equations are properly transformed so that the computational domain becomes time-independent. For the spatial discretization, a hybrid scheme with finite-differences and Chebyshev polynomials is applied, while a fractional time-step scheme is used for the temporal discretization. A wave absorption zone is placed at the outflow region in order to efficiently minimize reflection of waves by the outflow boundary. The numerical model is validated by comparison to the analytical solution for the laminar, oscillatory, current flow which develops a uniform boundary layer over a horizontal bottom. For the propagation of finite-amplitude waves over a rigid rippled bed, the case with wavelength to water depth ratio λ/d0 = 6 and wave height to wavelength ratio H0/λ = 0.05 is considered. The ripples have parabolic shape, while their dimensions — length and height — are chosen accordingly to fit laboratory and field data. Results indicate that the wall shear stress over the ripples and the form drag forces on the ripples increase with increasing ripple height, while the corresponding friction force is insensitive to this increase. Therefore, the percentage of friction in the total drag force decreases with increasing ripple height.
Improvement of Two-Component Model of the Finite Difference Lattice Boltzmann Method for a Gas-Liquid Flow Simulation
Authors: Tajiri Shinsuke , Tsutahara Michihisa , Wu Long
Published: March 2009

An Improved model of the finite difference lattice Boltzmann method which allows us to consider gas-liquid two component flows with a large density ratio like air-water flows was proposed. Simulations of the two component fluids which have a free interface and a large density ratio were demonstrated. The model which has compressibility of fluid and allows us to consider the pressure waves propagating in water like water hammers was presented. The basic idea is to decrease a density fluctuation by giving a large pressure gradient. The compressibility of liquid was controlled by choosing the bulk modulus. In order to simulate immiscible two fluids, the modulated diffusion scheme proposed by Latva-Kokko et al. was employed. The scheme is able to produce a smooth interface by allowing a certain amount of interface diffusion. The continuum surface force proposed by Brackbill et al. was employed as surface tension. A collapse of liquid column was calculated in order to confirm the relation between the inertia of liquid with a large density and the gravity, and the appropriate result was obtained.
Application of a Dynamic Global-Coefficient Subgrid-Scale Model for Large-Eddy Simulation in Complex Geometries
Authors: You Donghyun , Moin Parviz
Published: March 2009

The application of a dynamic global-coefficient subgrid-scale eddy-viscosity model for large-eddy simulation in complex geometries is presented. The model employs a dynamic procedure for closure of the subgrid-scale eddy-viscosity model developed by Vreman [Phys. Fluids 16, 3670 (2004)]. The model coefficient which is globally constant in space but varies in time is dynamically determined assuming the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation of which utilization was proposed by Park et al. [Phys. Fluids 18, 125109 (2006)]. Like the Vreman’s model with a fixed coefficient and the dynamic-coefficient model of Park et al., the present model predicts zero eddy-viscosity in regions where the vanishing eddy viscosity is theoretically expected. The present dynamic model is especially suitable for large-eddy simulation in complex geometries since it does not require any ad hoc spatial and temporal averaging or clipping of the model coefficient for numerical stabilization and requires only a single-level test filter.