bluuebunny/crossref_metadata_2025 huggingface dataset:
DGV’s Accuracy Dependence Upon Laser Beam Intensity Profile
Authors: Morrison Gerald L. , Suryanarayanan Saikishan
Published: July 2010

A Doppler Global Velocimeter (DGV) system was designed for use in high speed rotating equipment at the Turbomachinery Laboratory. Due to the rapidly varying periodic nature of flows inside turbines, compressors, and pumps, it is desirable to use a pulsed laser as the light source. An ND-YAG laser was selected for use based upon the 9 ns pulse duration and the ability for the laser to operate with a 15 MHz light bandwidth which is tunable to the absorption line filter used in the DGV system. However, when applied to the system it was discovered the DGV system did not work properly. The output of a line CCD array used to monitor the laser frequency was closely scrutinized. The light intensity across the laser beam was not Gaussian in nature but contained a very large amount of “noise”. Since the DGV system measures light intensity variations to infer Doppler shifts and hence velocity distributions, the rapidly spatially varying light intensity across the laser beam was suspected as the cause of the system’s inaccuracy. An analysis to quantify how the laser beam light intensity profile noise affects a DGV system accuracy is performed and possible remedies are suggested.
Bubble Effects on the Acoustic Doppler Velocimeter (ADV) Measurements
Authors: Birjandi Amir Hossein , Bibeau Eric
Published: July 2010

Acoustic Doppler Velocimeter (ADV) is a useful technique for measuring flow velocities with frequency variations of up to approximately 200 Hz in laboratory settings and in field applications. Although measuring velocity with ADV has advantages over other velocity measurement methods, this technique is sensitive to operating conditions: in addition to noise, the signal can contain spikes with large amplitudes, a disadvantage of ADV. In this study, the effect of bubbles on ADV signals is experimentally assessed in a laboratory setting. Bubbles can intersect the sampling volume and the acoustic beams creating spikes. The impact and amplitude of these spikes is a function of the bubble size and position when it crosses the ADV sampling volume and the acoustic beams. Bubbles that intersect the sampling volume generate spikes in all three velocity directions simultaneously; bubbles that intersect acoustic beams, which span between the sampling volume and the ADV receivers, impact the velocity data in one or two directions, and has a negligible effect in the third direction. Bubbles that intersect the X-direction acoustic beam create spikes in velocity data in both X- and Z-directions, but have no significant impact on the Y-direction; the Y- and X-directions have spikes and the Z-direction is not significantly impacted, when bubbles intersect the Y-direction acoustic beam. In addition, spikes increase the magnitude of the power spectra at high frequencies. Without bubbles, the autocorrelation in the time domain decreases in value as the time-lag increases, approaching zero after 5 seconds. The presences of bubbles cause a large peak in the autocorrelation at a zero time-lag, and no autocorrelation thereafter. Furthermore, the autocorrelation without bubbles permit turbulence length scales to be calculated because of the positive autocorrelation value; unless spikes are removed by using an appropriate filter when bubbles are present, turbulence length scales cannot be calculated because the autocorrelation is zero.
Dielectrophoretic Mixing With Novel Electrode Geometry
Authors: Kumar G. Naga Siva , Mitra Sushanta K. , Bhattacharjee Subir
Published: July 2010

Electrokinetic mixing of analytes at micro-scale is important in several biochemical applications like cell activation, DNA hybridization, protein folding, immunoassays and enzyme reactions. This paper deals with the modeling and numerical simulation of micromixing of two different types of colloidal suspensions based on principle of dielectrophoresis (DEP). A mathematical model is developed based on Laplace, Navier-Stokes, and convection-diffusion-migration equations to calculate electric field, velocity, and concentration distributions, respectively. Mixing of two colloidal suspensions is simulated in a three-dimensional computational domain using finite element analysis considering dielectrophoretic, gravitational and convective (advective)–diffusive forces. Phase shifted AC signal is applied to the alternating electrodes for achieving the mixing of two different colloidal suspensions. The results indicate that the electric field and DEP forces are maximum at the edges of the electrodes and become minimum elsewhere. As compared to curved edges, straight edges of electrodes have lower electric field and DEP forces. The results also indicate that DEP force decays exponentially along the height of the channel. The effect of DEP forces on the concentration profile is studied. It is observed that, the concentration of colloidal particles at the electrodes edges is very less compared to elsewhere. Mixing of two colloidal suspensions due to diffusion is observed at the interface of the two suspensions. The improvement in mixing after applying the repulsive DEP forces on the colloidal suspension is observed. Most of the mixing takes place across the slant edges of the triangular electrodes. The effect of electrode pairs and the mixing length on degree of mixing efficiency are also observed.
CFD Simulation of the Submerged Cofferdams Effect on the Operation of the Future Tocoma Hydroelectric Power Plant
Authors: Stanko Milan , Shmueli Andrea , Asuaje Miguel , Kenyery Frank , Montilla Gonzalo , Toscano Mari´a de los A´ngeles , Sa´nchez Richard
Published: July 2010

The Tocoma hydroelectric power plant, currently under construction, is located on the lower basin of the Caroni River in Bolivar State in Venezuela. This power plant will have 10 Kaplan turbines in its powerhouse that will generate approximately 2160 MW of hydroelectric power. During its construction, two cofferdams designated “A” and “B” will be built and afterwards will remain submerged. The main purpose of this experimental-numerical study is to analyze the possible future hydrodynamic effects of these structures on the operation of the Kaplan turbines. The presence of the submerged cofferdams could originate tridimensional hydrodynamic behaviors that could produce energy looses and operational and functional problems to the turbines. Two mathematical steady state single phase models using Computational Fluid Dynamics (CFD) Techniques and applying the commercial software ANSYS-CFX were developed. The first model represented the hydroelectric power plant reservoir that was quantitatively and qualitatively calibrated with a Froude Similarity 1:80 Scale Physical Model. Hydrodynamic flow patterns near to the intakes were found in the first model. Those patterns showed a non-uniform velocity profile in the unit’s intakes nearest to cofferdam “B”. The second mathematical model represented the study of the intake, the semi-spiral case and the Kaplan turbine. This model considers the non-uniform velocity profile that was found in the first model as an inlet boundary condition. Two methodologies were used to develop this model: one using two simulations with two overlapping physical domains, and the other one using the whole geometry. It was found that using overlapping domains in order to reduce the computational cost of the total simulation is a good way to obtain physical results with fair accuracy. The general results reported that the velocity profile at the intake of the powerhouse does not produce any stationary non uniform behavior on the velocity and pressure profiles in the unit compared to the uniform velocity profile case. This result could be an indicator that the non uniform condition at the intake of the Kaplan Turbines at Tocoma will not affect the normal operation conditions of the unit.
CFD Study of the Pressure Distribution on the Back of a 3-D Bluff Body (CUBE) of Air Flow in Different Reynolds Numbers
Authors: Izadi Mohammad Javad , Asghari Pegah , Delakeh Malihe Kamkar
Published: July 2010

The study of flow around bluff bodies is important, and has many applications in industry. Up to now, a few numerical studies have been done in this field. In this research a turbulent unsteady flow round a cube is simulated numerically. The LES method is used to simulate the turbulent flow around the cube since this method is more accurate to model time-depended flows than other numerical methods. When the air as an ideal fluid flows over the cube, flow separate from the back of the body and unsteady vortices appears, causing a large wake behind the cube. The Near-Wake (wake close to the body) plays an important role in determining the steady and unsteady forces on the body. In this study, to see the effect of the free stream velocity on the surface pressure behind the body, the Reynolds number is varied from one to four million and the pressure on the back of the cube is calculated numerically. From the results of this study, it can be seen that as the velocity or the Reynolds number increased, the pressure on the surface behind the cube decreased, but the rate of this decrease, increased as the free stream flow velocity increased. For high free stream velocities the base pressure did not change as much and therefore the base drag coefficient stayed constant (around 1.0).
Solid-Liquid Flow-Induced Erosion Prediction in Three-Dimensional Pump Casing
Authors: Pagalthivarthi Krishnan V. , Visintainer Robert J.
Published: July 2010

Solid-liquid flow-induced erosion wear prediction in a typical three-dimensional pump casing is dealt with. The two-phase flow field inside the three-dimensional pump casing is simulated using finite element modeling of mono-size particulate flow. Using this flow field and the concentration along the casing surface, wear rate is calculated using empirically determined wear coefficients. Wear rate along the three-dimensional casing surface and the location of high erosion rate are examined. Results show that the wear rate distribution is high near the cut water region (the region separating the total flow from the discharge flow). Wear is non-uniformly distributed and is high at some local spots. Even along other radial sections, wear rate varies significantly from the sides to the centerline of the casing.
Evaluation of Magnitude and Location of Solid Particle Erosive Wear in an Elbow Geometry Using CFD Analysis
Authors: Mazumder Quamrul H.
Published: July 2010

A number of factors that influence the magnitude of erosion include geometry, material of the impacting surface, impact angle, particle size and shape, particle velocity, flow condition and fluid properties. Among the various factors, particle size and velocity has been considered to be most important parameter that causes erosion. Particle size and velocity are influenced by surrounding flow velocities and carrying fluid properties. Higher erosion rates has been observed in gas solid flow in geometry where the flow direction changes rapidly such as elbow, tee, valves, etc due to local turbulence and unsteady flow behaviors. This paper presents the results of a Computational fluid dynamics (CFD) simulation of dilute gas-solid flow through a 90 degree elbow due to dynamics behavior of entrained solid particles in the flow. The effect of particle size and the corresponding location of erosion were investigated for 50, 100, 150, 200, 250 and 300 μm sand particles for three different flow velocities (15, 30 and 45 m/sec). The magnitude and location of erosion presented in the paper can be used to determine the areas susceptible to maximum erosive wear in the geometry along with corresponding rate of metal loss in these areas.
Experimental Study of Turbulent Flow in Two-Dimensional Porous Media
Authors: Bejatovic Sintia , Agelinchaab Martin , Tachie Mark F.
Published: July 2010

The paper reports on an experimental investigation of turbulent flow through model two-dimensional porous media. The porous media was bounded on one side by a solid plane wall and on the other side by a zone of clear fluid. The model porous media comprised of square arrays of circular acrylic rods that were inserted into precision holes drilled onto pairs of removable plates. The removable plates were then inserted into groves made in the side walls of the test channel. The rods fill about 59% of the channel height. Different combinations of rod diameter and center-to-center spacing were used to produce solid volume fractions that ranged from 0.11 to 0.44. The Reynolds number based on the bulk velocity of the approach flow and channel height was 16800. A high resolution particle image velocimetry (PIV) system was used to conduct detailed velocity measurements within the porous media and the adjacent clear fluid. The results demonstrate that permeability of the porous medium is more useful in correlating the flow characteristics than the porosity or solid volume fraction. Irrespective of rod diameter or spacing, a decrease in permeability of the porous medium produced a lower value of the dimensionless slip velocity. A decrease in permeability also produced higher resistance to the fluid flow through the porous medium. As a result, a larger fraction of the approach flow is channeled through the clear zone adjacent to a porous medium with lower permeability than those with relatively higher permeability. It was also observed that spatially averaged profiles of the mean velocities and turbulent quantities depend strongly on permeability.
Effects of the Divergence Angle on the Onset of Asymmetric Flow Through a Planar Diffuser
Authors: Nabavi Majid , Mongeau Luc
Published: July 2010

In this study, two-dimensional laminar incompressible and turbulent compressible flow through the planar diffuser (gradual expansion) for different divergence half angles of the diffuser (θ), and different Reynolds numbers (Re) was numerically studied. The effects of θ on the critical Reynolds number at which the onset of asymmetric flow is observed, were investigated. In the laminar flow regime, it was observed that for every values of θ, there is a critical Re beyond which the flow is asymmetric. However, in the turbulent flow regime, for θ ≥ 20°, even at low Reynolds number the flow is asymmetric. Only for θ ≤ 10°, symmetric flow was observed below a critical Re.
Application of Journal of Fluids Engineering CFD Verification Procedure to Flow Past Bluff Body Using Two Different Turbulence Models
Authors: Nanduri Jagannath R. , Celik Ismail B.
Published: July 2010

The ASME Journal of Fluids Engineering (JFE) recently adopted the grid convergence index (GCI) method as one of the methods among others to estimate the discretization error in CFD applications. The GCI method (based on Richardson extrapolation (RE)) is applied to CFD simulations of confined flow past a bluff-body and is used to evaluate the performance of two different turbulence models in predicting the flow. Four different grid densities (coarse, fine, finer and finest) are used in a 2D axisymmetric geometry along with the RNG k-ε model and the Reynolds stress transport (RST) turbulence models to predict the flow. A spline extrapolation (SE) method for the approximate error is also used to estimate the extrapolated value of the flow variables. The two models show monotonic and oscillatory convergence in various regions of the flow field. Results from the two turbulence models show different convergence behaviors. The results from the RE method as well as the SE method are assessed by comparing to the solution obtained on the finest grid as well as experimental data. The relative advantage of each of the methods is discussed. This study is a contribution towards testing the procedure proposed by JFE.
Flow Structure in the Near-Wall Region of a Submerged Impinging Jet
Authors: Hammad Khaled J. , Milanovic Ivana M.
Published: July 2010

An experimental investigation was performed to study the flow structure of a submerged water jet impinging normally on a smooth and flat surface using Particle Image Velocimetry (PIV). The jet issued from a 112 diameter, D, long pipe which ensured fully-developed turbulent flow conditions at the outlet. A semi-confined setting provided properly characterized flow boundary conditions. The Reynolds number based on jet mean exit velocity was Re = 16,000. The pipe-to-plate separation was varied between 1 and 8 pipe diameters. The current study focused on characterizing the flow structure close to the pipe outlet in the impingement and wall-jet regions. Statistically averaged mean and RMS velocities are reported for a 6D wide and 1D high, near-plate, rectangular region. A total of 155 × 24 or 3720 vectors were obtained, each representing the spatial average over a 0.0394D × 0.0394D area.
A Time-Accurate Projection Method for Low-Mach Number Variable Density Flows in Curvilinear Grids
Authors: Fard F. N. , Lessani B.
Published: July 2010

A time-accurate numerical algorithm is proposed for low Mach number variable density flows in curvilinear coordinate systems. In order to increase the stability of the method, a predictor-corrector time integration scheme, coupled with the projection method, is employed. The projection method results in a constant-coefficient Poisson equation for the pressure in both the predictor and corrector steps. The continuity equation is fully satisfied at each step. To prevent the pressure odd-even decoupling typically encountered in collocated grids, a flux interpolation technique is developed. The spatial discretization method offers computational simplicity and straightforward extension to 3D curvilinear coordinate systems, which are essential in the simulation of turbulent flows in complex geometries. The accuracy and stability of the algorithm are tested with a series of numerical experiments, and the results are validated against the available data in the literature.
The Flow Phenomena and the Non-Uniform Filling of the Unvulcanized Rubber in Process of Filling
Authors: Sakai Shintarou , Shigemitsu Toru , Fukutomi Junichiro , Matsuoka Tsukasa
Published: July 2010

Rubber products like oil seal are produced by vulcanization molding and the vulcanization molding of rubber product is performed by past experience, trial and error. It is important issues to decrease the product cost, reduce defective products and solve the environmental problems by saving natural resources. If the vulcanization moldings of rubber products are reappeared by computer simulation, it is very useful and it could contribute to solve the above problems. In order to reduce surplus rubber and defective products, numerical analysis of flow phenomena of unvulcanized rubber was performed using commercial software FIDAP. In several types of rubber mold model, the numerical analysis was conducted taken the characteristic of visco-elasticity fluid obtained by an experiment without considering the effect of heat. And experiments were conducted for the comparison of numerical results and actual phenomena. In the experiment, vulcanization process was stopped by arbitrary interval. Then the filling state and the shape of the rubber at each interval are observed in numerical and experiment results. The results showed that the filling state of numerical results represented good agreement with the experimental results. And it was clarified from the numerical analysis that shear stress increased when the unvulcanized rubber flowed in a narrow channel and there was the relation between pressure and velocity. In the present paper, the flow phenomena under the condition of the compression molding are shown and the optimum flow conditions are discussed from the numerical results. Furthermore mechanism of occurrence of defective products is considered with the experimental and the numerical results.
Three-Dimensional Steady Flow in Non-Linear Elastic Collapsible Tubes
Authors: Koh Wonhyuk , Kang Sungwoo , Cho Myunghwan , Yoo Jung Yul
Published: July 2010

Three-dimensional fluid-structure interaction problem arising from steady flow in non-linear elastic tube is studied numerically by using a finite element software, ADINA. Strain-energy density function is used for non-linear elastic analysis of solid material. Navier-Stokes equation coupled with elastic wall condition is solved for the fluid flow. To simulate interactions between the fluid and the solid domains, arbitrary Lagrangian-Eulerian (ALE) formulation is utilized. For validation, thin-walled linear elastic collapsible tubes is computed and compared with previous numerical results. The tube collapses into the buckling mode N = 2 and the results are in excellent agreement with a previous study. Then, the results for linear elastic tube are compared with those for non-linear elastic tube to show the effects of non-linear elasticity of the wall. The wall material is considered to be non-linear hyperelastic and isotropic. The non-linear elastic wall shows the tendency to preserve its shape more than the linear material. The deformation patterns, pressure distributions of the tube with non-linear elastic material are significantly different from those with linear elastic material.
Numerical Simulation of a Drop Sliding Down an Inclined Plane by Front-Tracking Method
Authors: Yamamoto Yasufumi , Uemura Tomomasa
Published: July 2010

In this paper, we present a front-tracking method containing an accurate representation of solid surface condition, and simulate a drop sliding down an inclined plate employing some slip models. Numerical results are compared with experimental observations by Le Grand et al. (Journal of Fluid Mechanics, 2005), and then which slip model is well-suited is examined. Drop shapes, in particular advancing and receding contact angles, and drop velocity reproduced by our simulations without explicit slip model are qualitatively good agreement with experimental observations for capillary number Ca<0.01.
Multi-Objective Design Optimization of a Mixed-Flow Pump
Authors: Takayama Yumiko , Watanabe Hiroyoshi
Published: July 2010

In most cases of high specific speed mixed-flow pump applications, it is necessary to satisfy more than one performance characteristic such as deign point efficiency, shut-off power/head and non-stall characteristic (no positive slope in flow-head curve). However, it is known that these performance characteristics are in relation of trade-offs. As a result, it is difficult to optimize these performance characteristics by conventional way such as trial and error approach by modifying geometrical parameters. This paper presents the results of the multi-objective optimization strategy of mixed-flow pump design by means of three dimensional inverse design approach, Computational Fluid Dynamics (CFD), Design of Experiments (DoE), response surface model (RSM) and Multi Objective Genetic Algorism (MOGA). The parameters to control blade loading distributions and meridional geometries for impeller and diffuser blades in inverse design were chosen as design variables of the optimization process. Pump efficiency, maximum slope in flow-head curve and shut-off power/head were selected as objective functions. Objective functions of pumps, designed by design variables specified in DoE, were evaluated by using CFD. Then, trade-off relations between objective functions were analyzed by using Pareto fronts obtained by MOGA. Some pumps which have specific performance characteristic (non-stall, low shut-off power, high efficiency etc.) designed along the Pareto front were numerically evaluated.
Characterization of the Automobile Defrosting System Through a Full-Scale Model
Authors: Kang Hyu-Goo , Jun Yong-Du , Lee Kum-Bae
Published: July 2010

Adequate visibility through the automobile windshield is of paramount practical significance, most perpetually at very low temperatures when ice tends to form on the windshield screen. The numerical solution was done by a finite volume CFD code and experimental investigations were performed to validate the numerical results. It was found that the airflow produced by the defrost nozzle does not cover the whole windshield area. The maximum temperature was observed over a value of 28°C at the vicinity of the defroster nozzle on the dashboard in the lower part of the windshield. The average windshield temperature range was −15 ∼ 12 °C, over a period of 30 min; which caused the frost to melt on the windshield. The melting period satisfies the NHTSA standard. The numerical predictions and the experimental results are in good agreement.
Unsteady Modelling of the Tip Clearance Flow in an Inlet Vaned, Low-Speed Axial Fan: Deterministic Interactions of Stator Wakes and Tip Vortex Structures
Authors: Ferna´ndez Oro Jesu´s Manuel , Argu¨elles Di´az Katia Mari´a , Santolaria Morros Carlos , Galdo Vega Mo´nica
Published: July 2010

In last years, numerical modelling has reached a significant level of maturity in the analysis of axial turbomachinery flows. Full-unsteady, three-dimensional computations have been demonstrated as a powerful tool to characterize viscous phenomena on blade row interactions and blade passage structures. In particular, major effects have been focused on the study of deterministic fluctuations in order to quantify the impact of periodic unsteadiness on the time-averaged flow. An additional complexity concerns to the influence of the tip vortex structures on the deterministic patterns. Hence, some researchers have advanced experimental evidences on the contribution of tip leakage flow to the time-resolved distributions. Tip vortex, shedding energy at a wide range of scales, has been shown to be significant in the description of the spanwise momentum transfer and the appearance of mixing losses. Recently, the authors have investigated the impact of the tip vortex on the passage flow structures of a jet fan with symmetric blades. This work revealed valuable information about tip vortex transport in low-speed axial turbomachinery and demonstrated the ability of commercial codes to simulate three-dimensional, vortical structures with high accuracy. The present paper takes advantage of the same numerical methodology to highlight the influence of the deterministic correlations that describe the stator-rotor interaction on the tip vortex in a single-stage axial fan. Up to now, few works addressing deterministic contributions over the tip leakage flow are available in the literature, so more investigation is needed to understand the complexity of these physical mechanisms. Our contribution to the topic is based on a 3D, unsteady numerical simulation of the flow within a reduced periodic domain of the full-annulus axial stage, composed by only 3-vane and 2-blade passages. This simplification allows an enhancement of the grid density when massive parallel computations are employed. Also, comparison with experimental data measured using hot-wire anemometry is provided to validate the numerical model. The results show how the non-uniformities of the stator wake-core structure in the relative frame of reference are conditioning the tip leakage flow, addressing the influence of the operating conditions or the interrow spacing. The final objective is to provide levels of instabilities in the tip vortex derived from deterministic non-uniformities associated to vane-to-vane flow patterns, applicable in further modelling of deterministic stresses.
Influence of the Pressure Load in the Efficiency of a Longitudinal Ventilation System in Road Tunnels
Authors: Galdo-Vega Mo´nica , Santolaria-Morros Carlos , Ferna´ndez Oro Jesu´s Manuel , Argu¨elles-Di´az Katia Maria
Published: July 2010

The longitudinal ventilation system (LVS) efficiency in road tunnels is conditioned by geometric and operational parameters. Typical geometric parameters are the length of the tunnel, its slope and the transversal section. All these factors are generally fixed and thus not modifiable in the regular operation of the facility. On the other hand, operational parameters, like the working fans layout, the environmental conditions or the traffic density are case-sensitive and susceptible to influence the baseline performance of the ventilation system. In the present study, different pressure gradients, established between inlet and outlet location of the jet fan influence, are analyzed. This static resistance is shown to have a significant impact on the momentum transfer established between the jet expansion and the bulk flow inside the tunnel. For moderate pressure gradients, the jet discharged from fan is relativity well-mixed, allowing to reach uniform flow conditions in the streamwise direction. When the adverse pressure gradients become severe, the high-velocity flow is blocked, unable to mix out in the inter fan spacing and losing spanwise uniformity. At critical conditions, large recirculation areas can be developed within primary flow structures, generating turbulence and important energy losses, and even inducing reverse flow at the tunnel exit. The extreme operating conditions of a longitudinal ventilation system in a road tunnel have been studied using a 3D numerical simulation. Preliminary analysis for grid sensitivity and election of an accurate turbulence closure were performed to guarantee a valuable modeling. Following, systematic computations over a cluster of PC’s were executed using the well-tested Fluent code. RANS modeling with RSM scheme allowed a satisfactory description of three-dimensional vortical structure in the recirculation zones, especially for adverse pressure gradients. At this point, numerical results have provided a comprehensive overview of the mechanism associated to the momentum transfer of the jet expansion, comparing the performance for zero-pressure gradients with those observed for adverse conditions. Also, this paper gives valuable information about practical limits of the LVS, advancing operational conditions that compromise the ventilation efficiency.
Analysis for Rarefied Gas Flow in a Rotating Cylinder
Authors: Futagami H. , Ninokata H.
Published: July 2010

Behaviors inside rotating cylinders where the range of operating pressure is very wide, i.e. from subatmospheric to almost vacuum are subject of this study. The flow near the rotating axis is very rarefied. If a flow becomes rarefied, the flow cannot be treated as that of a continuum media. Therefore the flow cannot be analyzed by the method based on solving Navier-Stokes equation. One of the promising methods is considered to be DSMC (Direct Simulation Monte Carlo) method based on Boltzmann equation ([1]). In this paper, fundamental validation analyses related to isotope separation in a rotating cylinder calculations of endplate type centrifuge were performed for the parametric study, with DSMC. The results were compared with the experimental results by Groth et al ([2]). The validity of the calculations and its limit were also discussed.
Analytical Solution of Chamber Effective Length in the Axial Engine
Authors: Dehghani S. R. , Mozafari A. A. , Saidi M. H. , Ghafourian A.
Published: July 2010

In this research, effective length of one-dimensional combustion in a dilute monopropellant spray, constant area and fixed volume chamber is analytically predicted. A new evaporation rate in the form of dk+1 relation is introduced. In the case of controlling vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to one and in some cases vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in the design of combustion chambers with optimum length and with using vaporization rate of R = R0〈r〉0k/〈r〉k. Spray equation and distribution function in one-dimensional coordinate in direction of chamber axis is used as the governing equation. Multiplying velocity and displacement variables by simplified spray equation and some manipulation lead to a final form of integral equation. Definition of β1β3 as criteria will simplify the complex integral equation to a solvable relation. Results provide dimensionless velocity of droplets (from initial state to completely vaporization) and chamber effective length for various values of k. The results obtained by employing dk+1 relation show that increasing k increases in droplet vaporization rate as well as oxidizer velocity and decreases in dimensionless effective length of chamber. Also they show that for β1β3 ≥ 25 deviation of dimensionless velocity from published data by Dehghani et al. (2009) is less than 3%.
A Non-Symmetrical Swirling Jet as an Example of a Completely Described Assessment Experiment
Authors: Wilson Brandon M. , Smith Barton L. , Spall Robert , McIlroy Hugh M.
Published: July 2010

The standard of a completely described experiment for CFD validation is demonstrated by using experimental and numerical models of swirling jets as an example. The experiment is designed to contain relevant physics (e.g. swirl) but without regard for generality or direct scaling to realistic geometries. Also, the design allows for direct measurement of the inflow (mean and statistics). The swirling jets experience vortex breakdown, have non-symmetric inlet profiles, and have Reynolds numbers of 3650, 2560, and 550 with Rossby numbers of 0.63, 0.59, and 0.73 respectively. The two larger Re cases resulted in turbulent flow inside the jet conduit upstream. All of the jets became turbulent rapidly after leaving the exit. It is demonstrated that the numerical simulations will provide more accurate results when the inlet conditions of these non-symmetric swirling jets are fully described.
Numerical Simulations of Solid Oxide Fuel Cells Operating on Coal Syngas: A Parametric Study
Authors: Elizalde-Blancas Francisco , Pakalapati S. Raju , Cayan F. Nihan , Celik Ismail B.
Published: July 2010

Fuel cells are considered to be one of the main sources of future power supply around the world because of their many desirable features; technology virtually free of pollution, the ability to use alternative fuels other than fossil fuels, and higher efficiencies than combustion engines. Solid Oxide Fuel Cells (SOFCs) can operate on a wide range of fuels, particularly with coal syngas. However, several issues have to be solved before SOFC’s operating on coal syngas can be introduced into the market as a reliable and cost viable technology. Numerical simulations can be used in conjunction with experiments to assist in resolution of such barriers. In the present work, a three-dimensional model is used to study the performance of a SOFC running on coal syngas operating at various conditions. The code is capable of simulating several species in the fuel stream, such as methane, steam, carbon monoxide, hydrogen, carbon dioxide. Due to the presence of hydrogen and carbon monoxide, simultaneous electrochemical oxidation of both fuels is considered. Internal reforming and water gas shift reaction are other processes that are taken into account. Simulations of typical anode-supported button cells are performed to assess the effects of cell operating temperature, fuel composition and CO electrochemistry on the performance of the button SOFCs.
Local Measurements in Cavitating Flow by Ultra-Fast X-Ray Imaging
Authors: Coutier-Delgosha O. , Vabre A. , Hocevar M. , Delion R. , Dazin A. , Lazaro D. , Gmar M. , Fezzaa K. , Lee W-K.
Published: July 2010

The present paper presents an experimental method to measure velocity fields in a cavitating flow. Dynamics of the liquid phase and of the bubbles are both investigated. The measurements are based on ultra fast X-ray imaging performed at the APS (Advanced Photon Source) of the Argonne National Laboratory. This is collaboration between research teams devoted to fluid mechanics (LML laboratory, Laboratory for water and turbine machines) and experts in X-ray imaging (French atomic commission, Argonne National Laboratory). The experimental device consists of a millimetric Venturi test section associated with a transportable hydraulic loop. Various configurations of velocity, pressure, and temperature have been investigated. This first paper focuses on the experimental equipment and process, and also the description of the image processing which is performed to analyze the results and obtain the velocity fields of both phases within the cavitating areas. Promising preliminary results are also presented.
Flow Induced Stresses in a Francis Turbine Runner Using Computer-Based Design Tools
Authors: Franco-Nava Jose´ Manuel , Dorantes-Go´mez Oscar , Rosado-Tamariz Erik , Ferna´ndez-Da´vila Jose´ Manuel , Rangel-Espinosa Reynaldo
Published: July 2010

The stress analysis of the runner due to different loading is one of the most important tools that contribute its structural integrity evaluation. Finite element method has shown to be a strong numerical technique to provide good engineering accuracy. In this paper, the flow induced stresses in a Francis turbine runner is presented by using the finite element analysis. The runner geometry considered within the computational domain was modelled by using a three-dimensional laser triangulation scanner coupled with a portable coordinate measurement system. The runner geometry was generated by a number of 3D sub models, one for each of the main components of the runner, crown, band and a blade. In order to obtain a blade geometry a portable coordinate measurement system based on optical digitalization technology (scanner technology) was used. Because of symmetry, only a section of the runner domain was used for the finite element analysis. The runner was modeled with twenty-node solid elements. Loads due to pressure on the blade were derived from CFD computations for the runner at different power conditions (100%, 85% and 75%) for a medium head hydro power plant. CFD computations were carried out using the Finite Volume Method implement within FINE™/Turbo by NUMECA. The turbulence mathematical model used for the CFD computation was the Sparlart-Allmaras. The mesh of the turbine runner included different computational domains. For the runner blades the computational domain (mesh block) was defined in order to capture the complete blade row. All mesh blocks were structured hexahedral. Centrifugal force based on the rotational speed was considered. Also, a combined type loading analysis was computed including both pressure and centrifugal force. Appropriate boundary conditions were set in order to obtain the results due to the different type of analysis. The number of finite elements included in the FEM model was able to capture the pressure gradients on the blade surfaces obtained from the CFD results, which were investigated by application of a three dimensional Navier-Stoke commercial turbomachinery oriented CFD code. Analysis of the flow through the spiral case and stay vanes was carried out so as to include appropriate flow effects induced by these components and boundary conditions at the inlet of the wicket. A CFD analysis for the wicket and runner was carried out to generate the so called CFD reference solution. The analysis presented in this paper represents an initial characterization in order to increase understanding about combined loads acting on blades and to establish a reference state of stresses further comparison after refurbishments or optimization of the runner blades for a medium head hydroelectric power station.
CFD Performance Evaluation and Runner Blades Design Optimization in a Francis Turbine
Authors: Franco-Nava Jose Manuel , Rosado-Tamariz Erik , Dorantes-Gomez Oscar , Ferna´ndez-Da´vila Jose´ Manuel , Rangel-Espinosa Reynaldo
Published: July 2010

The application of computational fluid dynamics (CFD) in the redesign or rehabilitation of hydraulic turbines appears to be necessary in order to improve their efficiency and cost-effectiveness beyond the traditional redesign practices. The runner geometry considered within the computational domain was modelled by using a three-dimensional laser triangulation scanner coupled with a portable coordinate measurement system. The runner geometry was generated by a number of 3D sub models, one for each of the main components of the runner, crown, band and a blade. In order to obtain a blade geometry a portable coordinate measurement system based on optical digitalization technology (scanner technology) was used. A numerical optimization methodology is developed and applied to a Francis turbine. The hydrodynamic performance analysis was investigated by application of a three dimensional Navier-Stoke commercial turbomachinery oriented CFD code. Analysis of the flow through the spiral case and stay vanes was carried out so as to include appropriate flow effects induced by these components and boundary conditions at the inlet of the wicket. A CFD analysis for the wicket and runner was carried out to generate the so called reference solution. Then, the runner blades design was optimized by a process implemented in a commercial CFD code which combines genetic algorithms and a trained artificial neural network (ANN). A database of geometries and their respective CFD computations were computed in order to determine the optimum geometry for a given objective function. The flow within hydraulic turbines has a thin boundary layer and noticeable pressure gradients. Hence, the CFD computations were carried out using the Sparlat-Allmaras turbulence model. After optimization cycle convergence, an increment not only in efficiency but also in power was obtained. The optimized runner represented by a parametric model achieves considerably higher efficiency than the reference runner. Efficiency versus power curve was used to compare data from measurements at the power station for the reference runner versus the parametric optimized runner model. Results have shown that application of CFD based optimization can modify and improve runners design so as to increase the efficiency and power of installed hydraulic power stations.
Dispersion Characterization Rig
Authors: Gomez-Markovich Y. , Gomez L. , Mohan R. , Shoham O. , Kouba G. , Avila C.
Published: July 2010

The flow behavior and stability of oil-water dispersions was investigated by means of a novel commercialized Dispersion Characterization Rig (DCR). The breakup and coalescence of the droplet were examined through the separation process in a batch trap separator, located downstream of a series of mixers/chokes. Height vs. time profiles of the coalescing and sedimenting interfaces were obtained. Different experimental parameters were studied on the separation process: properties of oil-phase (light and heavy oil) and aqueous-phase (tap, distilled and brine); temperature; pressure, initial dispersion height, and water-cut. Normalization of experimental profile results were proposed with respect to both height and time. The Avila [3] batch separation model predictions were compared with the experimental data. The model is capable of predicting the sedimenting and coalescing profiles, average droplet size, and its deviation about the mean. Model predictions show good agreement with the experimental data.
CFD Modeling of Two-Phase Gas-Liquid Slug Flow Using VOF Method in Microchannels
Authors: Mehdizadeh A. , Sherif S. A. , Lear W. E.
Published: July 2010

Despite of the fact that numerical simulation of two-phase flows in microchannels has been attempted by many investigators, most efforts seem to have failed in correctly capturing the flow physics, especially the slug flow regime characteristics. The presence of a thin liquid film in the order of 10 μm around the bubble (sometimes called gas pocket or gas slug) may be a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field. Thus, there is a strong motivation to employ numerical simulation methods in order to avoid some of the experimental difficulties. In this paper, the characteristics of two-phase slug flows in microchannels are calculated with the help of the Volume-of-Fluid (VOF) method. Formation of the slugs for different superficial velocities, Capillary numbers, and gas volume fractions are investigated. The minimum mesh resolution required to capture the liquid film surrounding the gas bubble is reported employing a dynamic mesh adaption methodology with interface tracking. Results are shown to be in good agreement with experimental data and empirical correlations.
Aerodynamic Degradation of Iced Airfoils: Experiments and CFD Simulations
Authors: Chara Z. , Horak V. , Rozehnal D.
Published: July 2010

The phenomenon of in-flight icing may affect all types of aircraft. Presence of ice on wings can lead to a number of aerodynamic degradation problems. Thus, it is important to understand the different ice shapes that can form on the wings and how they affect aerodynamics. When compared to wings without ice, wings with ice indicate decreased maximum lift, increased drag, changes in pressure distribution, stall occurring at much lower angles of attack, increased stall speed, and reduced controllability. The in-house ice accretion prediction code R-ICE using 2-D panel method was developed. The CFD simulation with the software ANSYS CFX 11.0 was used to simulate flow around iced airfoils NACA 0012. These airfoils were experimentally investigated in a wind tunnel. The paper presents a comparison of lift and drag coefficients experimentally observed and numerically simulated.
Modeling of Liquid Entrainment in Gas in Horizontal Pipes
Authors: Mantilla I. , Gomez L. , Mohan R. , Shoham O. , Kouba G. , Roberts R.
Published: July 2010

The purpose of the present study is to improve the current prediction capabilities of the entrainment fraction in horizontal gas-liquid flow. Since it is recognized that waves at the gas-liquid interface are the main source of entrainment, an experimental and theoretical work has been carried out to characterize the waves at the gas-liquid interface and to develop a model for entrainment calculations based on such characteristics. The model consists of three sub-models, namely, onset of entrainment, maximum entrainment and entrainment values in between. The onset of entrainment model determines the conditions at which the gas starts shearing the wave crests through a force balance between drag and surface tension forces. The maximum entrainment model provides the maximum fraction of liquid that can be entrained at high gas velocities by integration of the turbulent velocity profile to a determined dimensionless film thickness within the buffer sub layer. The entrainment fraction in between onset and maximum boundaries is calculated from an equilibrium between atomization and deposition rates. The atomization rate is calculated by first determining the wave mass flux in the liquid film and second by calculating the fraction of a single wave that is sheared by the gas through a force balance. The deposition rate is calculated as a linear function of the droplet concentration in the gas. Closure relationships have been developed from data for wave celerity, frequency, amplitude and width which are used in the entrainment model. A review of the most used correlations for calculating the entrainment fraction is presented and their performance evaluated. The present model shows better prediction than available models when compared to the acquired experimental data and the available experimental data in the literature.
Discrete Element Simulations of Granular Flow in a Pebble Bed Reactor
Authors: Zhao Xiang , Montgomery Trent , Zhang Sijun
Published: July 2010

This paper presents discrete element simulations of granular flow in a rectangular hopper model of the pebble bed reactor (PBR). Two flow conditions with/without granular materials recycled back are considered in this work. For both flows, the simulations have been conducted under comparable conditions so that the similarity and difference between them can be examined. The distributions of the physical properties including flow patterns, velocity and flow structure are also investigated. Moreover, the mean velocity, diffusion and particle mixing, the effects of wall friction have been analyzed based on the simulation results. The implications for the reactor design and fundamental research on granular flow physics are discussed as well.