bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of the Onset of Gas Entrainment Through a Finite-Side Branch
Authors: Ahmed M. , Hassan I. , Esmail N.
Published: March 2009

A theoretical investigation has been conducted for the prediction of the critical height at the onset of gas entrainment during single discharge from a stratified two-phase region through a side branch with a finite diameter. Two different models have been developed including a new criterion for the onset of gas entrainment, a simplified point-sink model and a finite-branch model. The results of the predicted critical heights at the onset of gas entrainment showed that the finite-branch model approaches the physical limits at low Froude numbers. However, as the values of the Froude number increased, the predicted values of both models eventually converged to the same value. Based on the results of the models, the critical height corresponding to the onset of gas entrainment was found to be a function of Froude number and fluid densities. The results of both models are compared with available experimental data. The comparisons illustrate a very good agreement between the measured and predicted values.
Performance Evaluation of New Designs of Wind Towers
Authors: Bahadori Mehdi N. , Pakzad Amir R.
Published: March 2009

Wind towers are architectural designs employed for natural ventilation and passive cooling of buildings. In this study, it is shown that the performance of these towers can be improved appreciably by incorporating evaporative cooling in them. Two designs, called wetted columns and wetted surfaces, were employed, and their performances were evaluated and compared with those of the conventional towers. It is found that both designs can deliver air to the building they serve at higher flow rates and at temperatures very near the ambient air wet-bulb temperatures. In general, the wind tower with wetted columns performs better in areas with relatively high wind speeds, whereas the designs with wetted surfaces performs better in areas with no winds, or with very low wind speeds.
The Influence of a Diffuser Width on the Unsteady Performance of a Centrifugal Compressor Stage
Authors: Engeda Abraham
Published: March 2009

An experimental investigation was conducted to determine the effect of the vaneless diffuser width on the unsteady flow performance of a centrifugal compressor stage. Two compressor configurations with different vaneless diffuser width were investigated at four different impeller speeds and compared in the frequency and time domain. Only one diffuser rotating stall but different types of impeller rotating stalls were detected. The experiments show that the diffuser has a strong influence on the flow in the impeller including in areas way upstream. Analysis of the results indicated: • With increasing diffuser width the onset of impeller rotating stall was shifted to lower flow rates. • With increasing diffuser width the frequencies of the rotating stalls decreased. • There is a common tendency in most of the experiments to lower numbers of rotating cells with increasing relative speed. The impeller rotating stalls can be subdivided in a slow pattern with a relative speed to the impeller of 0.21 to 0.29 and a fast pattern with a relative speed of 0.50 to 0.56. This occurrence of two rotating pressure patterns confirms analytical results presented in previous investigations.
Concept Development of an Oscillating Tidal Power Generator
Authors: Campbell Magnus
Published: March 2009

The Engineering Business Ltd. (EBL) have developed a patented system for generating electricity from oscillating hydroplanes driven by flowing water. The concept started development with the award of a Smart Award from the UK governments Department of Trade and Industry (DTI) in 1998, which led to the development of the Active Water Column Generator (AWCG). The AWCG was a simple, sea / air interface device which demonstrated, through the actuation of hydroplanes in moving water, that power could be generated. However, this concept suffered from inherent size and vulnerability limitations. It was decided to alter the basic form such that it is now seabed mounted, and therefore protected from the worst storm and wave effects. This concept, known as Stingray, is being developed under the New and Renewable Energy Research and Development program run by the DTI. Following the successful conclusion of the first phase of work, a fast-track 15 week feasibility study undertaken in the last quarter of 2001, phase two of the program is well under way. This involves a full design study, for 2002/3, to design, install, operate, decommission and evaluate a 150kW demonstrator — the first of its kind internationally. This paper describes the progression from concept to demonstrator design, focussing on the modelling work undertaken in the initial investigation and plans for its subsequent validation. It outlines mathematical and physical modelling techniques used and then gives a brief summary of the findings to date.
Experimental Research and Turbulent Flow Simulation of the Updraft Free-Exit-Flow Hydropower Turbine System
Authors: Li Haifeng , Wu Yulin , Kao David T.
Published: March 2009

During development of the updraft free-exit-flow hydropower turbine system, serious attention was paid to impact of the traditional turbine system to environment. The paper presents results of experimental research and three-dimensional turbulent flow simulation of the runner. The experiment demonstrated that, on one hand, the system can enhance exit flow aeration and downstream water quality; on the other hand, it gives good results in terms of its power production efficiency, about 85%. Based on the time-averaged Navier-Stokes equations and standard k-ε model, the SIMPLEC algorithm was applied for the numerical analysis. To guarantee credibility of the calculation, FLUENT5.5 code was used, which can provide distribution of pressure and velocity respectively. With comparison between the experimental data and calculating results, it can be concluded that flow simulation can be an effective tool for predicting performance and optimizing design of new turbine runner.
Slot Jet Impinging a Curved Wall
Authors: Gilard V. , Brizzi L.-E.
Published: March 2009

In order to study the aerodynamics of a slot jet impinging a concave wall, flow visualisations, velocity measurements by PIV and pressure measurements are carried out. A statistical data processing allows us to obtain the mean velocity fields and the Reynolds stresses. Among the studied parameters, the effect of the relative curvature of the wall is studied in particular because of a jet beating phenomenon observed for a low relative curvature. Three flow modes are then described.
Numerical and Experimental Investigations of a Turbulent Jet From a Round Ribbed Tube
Authors: Hoang Huy Trong , Rahai Hamid R.
Published: March 2009

Results of numerical and experimental investigations of turbulent jet from a round ribbed tube are presented. The round ribbed tube is a coil-inserted tube. The ratio of the coil wire diameter to the tube inside diameter, d/D, is 0.1 and the ratio of the coil pitch spacing to the tube inside diameter, p/D, is 1.2. The coil is placed inside the tube such that it terminates at the tube outlet. The standard k-e turbulence model along with the control volume method is used in the numerical calculations. The numerical results provided more insights into the flow characteristics in the radial planes. Results show that the coil inserts generates a weak swirl at the tube outlet that dissipates at an approximate distance of X/D = 1 where at this location the generated free vortices off the coil become the main mechanism behind the entrainment and mixing process. Comparisons of the numerical and experimental results show over estimation of the results by the numerical method.
Simulation of Turbulent Flow in a Channel Partially Occupied by a Porous Layer Considering the Stress Jump at the Interface
Authors: de Lemos Marcelo J. S. , da Silva Renato Alves
Published: March 2009

Environmental flows of extreme importance, such as turbulent atmospheric boundary layer over thick rain forests, may benefit from more realistic mathematical models. Accordingly, flow over layers of dense vegetation can be characterized by some sort of porous structure through which a fluid permeates. For hybrid media, involving both a porous structure and a clear flow region, difficulties arise due to the proper mathematical treatment given at the interface. The literature proposes a jump condition in which shear stresses on both sides of the interface are not of the same value. This paper presents numerical solutions for such hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in turbulent regime. One unique set of transport equations is applied to both regions. Effects of Reynolds number, porosity, permeability and jump coefficient on mean and turbulence fields are investigated. Results indicate that depending on the value of the stress jump parameters, a substantially different structure for the turbulent field is obtained.
Hybrid RANS-LES Modelling With the Renormalization Group
Authors: De Langhe Chris , Merci Bart , Dick Erik
Published: March 2009

A two-equation turbulence model that can adjust itself from RANS to LES regimes is constructed using the renormalization group. When the grid-spacing gets to coarse for LES, the model tends to a RANS model. In well-resolved regions the model results in a LES subgrid-model. The renormalization group procedure leads to transport-equations that are dependent on the filterwidth and contain no adjustable constants.
Wear and the Total Cost of Ownership of Slurry Pumps
Authors: Sellgren Anders , Addie Graeme , Pagalthivarthi Krishnan
Published: March 2009

When slurry pumps are considered for procurement for a solids transport requirement, decisions have often been made on initial price rather than the total cost of ownership (TCO). Depending on the type of solids to be transported, the design (and selection) of the pumps and the way they are operated; the wear, part replacement, and downtime can be a significant portion of the overall operating cost. Wear lives are here estimated with recently developed numerical simulation procedures for pump impeller and suction liner wear together with an established wear modeling schema for shells. White iron material is considered and the resulting modeled wear does not include any uncertainty related to the inherent stochastic nature of wear. It is shown in an example how shell, impeller and suction wear life and relative costs are related to different pump size and rotary speed designs. The results form a basis to find the best compromise between pump wear, power and capital cost in an overall TCO-perspective including the users practice and maintenance strategy.
Erosion Characterization of Coated Superalloys in Turbomachinery Applications
Authors: Tabakoff Widen , Hamed Awatef
Published: March 2009

The ingestion of suspended particles by high performance turbomachinery reduces engine efficiency and life. New developments in blade coating materials have contributed to compressor and turbine design improvements. A knowledge of the important phenomna associated with material erosion by particulate flow is required in the design. This paper gives an overview of the experimental studies of the erosion characteristics of coated superalloy blades conducted at the University of Cincinnati’s test facilities for blade and coating materials erosion will be described. Results will be presented and discussed for the erosion characteristics of various blade materials and coatings. The investigated coatings are produced via plasma spray, detonation guns, chemical vapor deposition (CVD), and physical vapor deposition (PVD).
Relationships Between Lagrangian and Eulerian Scales: A Review
Authors: Huilier Daniel G. F.
Published: March 2009

The purpose of the present communication is to summarize the state-of-the art knowledge of the existing relationships between Eulerian and Lagrangian statistics in the literature. It will focus on integral scales, especially the classical Eulerian scales (such as those classically obtained from a fixed hot-wire or LDA control volume), the interesting moving Eulerian time scale (that obtained by a sensor which would move with the mean velocity) and the Lagrangian integral scale, most important for Lagrangian turbulent diffusion and dispersion simulations.
Out-of-Plane Motion Effects in Microscopic Particle Image Velocimetry
Authors: Olsen Michael G.
Published: March 2009

In microscopic particle image velocimetry (microPIV) experiments, the entire volume of a flowfield is illuminated, resulting in all of the particles in the field of view contributing to the image. Unlike in light-sheet PIV, where the depth of the measurement volume is simply the thickness of the laser sheet, in microPIV, the measurement volume depth is a function of the image forming optics of the microscope. In a flowfield with out-of-plane motion, the measurement volume (called the depth of correlation) is also a function of the magnitude of the out of plane motion within the measurement volume. Equations are presented describing the depth of correlation and its dependence on out-of-plane motion. The consequence of this dependence and suggestions for limiting its significance are also presented. Another result of the out-of-plane motion is that the height of the PIV signal peak in the correlation plane will decrease. Because the height of the noise peaks will not be affected by the out-of-plane motion, this could lead to erroneous velocity measurements. An equation is introduced that describes the effect of the out-of-plane motion on the signal peak height, and its implications are discussed.
Oscillatory Free-Surface Displacement in an Orifice at Surface Amplitudes Below Those Required for Droplet Formation
Authors: Daniels Brian J. , Liburdy James A.
Published: March 2009

The oscillatory free-surface displacement in an orifice periodically driven at the inlet is studied theoretically and experimentally. A potential flow analysis is applied using two different sidewall boundary conditions: no flow through the wall, and no slip at the wall. Both analyses result in surface shapes defined by Bessel functions, but with significantly different frequencies associated with the discrete modal shapes. Experimental results for two orifice diameters, 1180 µm and 794 µm, verify the general shape of the surface displacement but show a significant downward shift of the measured modal frequencies from the predicted values. This shift is shown to be a function of mode number and is thought to be a consequence of orifice edge effects.
Measurement and Modeling of the Fluctuating Wall Pressure Field Beneath Transitional Boundary Layers
Authors: Snarski Stephen R.
Published: March 2009

Measurements of the fluctuating wall pressure field across the transition region of a flat plate zero pressure gradient boundary layer have been performed with a 64-element linear array of sub-miniature hearing-aid microphones. The measurements provide a unique description of the formation, convection, and growth of turbulent spots in the transition zone and insight into a potential source of low-wavenumber energy. A model for the nonhomogeneous wavenumber-frequency spectrum has been formulated based on the observed spatio-temporal properties of the field. Measured array-averaged wavenumber-frequency spectral levels for the transitional boundary layer collapse with fully turbulent spectra in the vicinity of the convective ridge when scaled by intermittency, similar to previous findings for single point spectra. The transition zone convective ridge is broader, however, consistent with the notion of rapidly evolving (versus equilibrium) structures. Insight into the low-wavenumber portions of the spectra requires an improved array phase calibration. Wavelet based transform methods are being pursued to understand the evolution of spectral components during spot formation and to resolve the space-varying wavenumber content of the field.
Influence of a Splitter Plate in the Near Wake of a Divergent Trailing Edge
Authors: Neau L. , Pruvost J. , Rodriguez O. , Loc Ta Phuoc
Published: March 2009

This paper discusses experimental results aimed at defining a base drag reduction device based on splitter plates. The unsteady 3D nature of the flow is studied by Schlieren photographies, particle image velocimetry and measurement of the total unsteady lift and drag loads.
Unsteady RANS Computations of the Flow Past an Airfoil in the Wake of a Rod
Authors: Boudet Je´roˆme , Casalino Damiano , Jacob Marc C. , Ferrand Pascal
Published: March 2009

Two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved in order to simulate the interaction between a Ka´rma´n vortex street shed from a rod and a NACA-0012 airfoil in the wake of the rod. Two closure turbulence models are tested, a linear and a nonlinear k-ω model, for a chord based Reynolds number Rec ∼ 4.8105. These models provide consistent results in terms of both mean and fluctuating flow quantities. Insight into the instantaneous vorticity field shows that the vortex shedding pattern near the wall is quite well predicted, despite an over-estimated frequency. Downstream, computations always exhibit head-on interactions of the vortices with the airfoil leading edge whereas the experiments show a more variable configuration.
Large Eddy Simulation of the Compressible Flow Over an Open Cavity
Authors: Oh Keon-Je , Colonius Tim
Published: March 2009

Large eddy simulation is used to investigate the compressible flow over a open cavity. The sub-grid scale stresses are modeled using the dynamic model. The compressible Navier-Stokes equations are solved with the sixth order accurate compact finite difference scheme in the space and the 4th order Runge-Kutta scheme in the time. The buffer zone techniques are used for non-reflecting boundary conditions. The results show a typical flow pattern of the shear layer mode of oscillation over the cavity. The votical disturbances, the roll-up of vorticity, and impingement and scattering of vorticity at the downstream cavity edge can be seen in the shear layer, while the flow inside the cavity is relatively quiescent. The predicted acoustic resonant frequencies are in good agreement with those of the empirical formula. The mean flow streamlines are nearly horizontal along the mouth of the cavity. The pressure has its minimum value in the vortex core inside the cavity. The variation of the model coefficient predicted by the dynamic model is quite large between 0 and 0.3. The model coefficient increases in the stream-wise evolution of the shear layer and sharply decreases near the wall due to the wall effect.
Energy Balance in Vortex-Induced-Vibration of an Inverted Pendulum
Authors: Dong P. , Voorhees A. , Atsavapranee P. , Kuchnicki S. , Benaroya H. , Wei T.
Published: March 2009

High resolution Digital Particle Image Velocimetry has been used to measure terms in the integral fluid energy transport equation. These data have been incorporated into a scientifically rigorous Hamilton’s Principle approach for modeling fluid-structure interactions. The interaction being modeled is the vortex-induced motion of a circular cylinder mounted like an inverted pendulum in a water tunnel. This paper describes the experimental methodology used to acquire key modeling data, i.e. kinetic energy transport and work across the boundaries of an integral control volume. There is also a presentation of a simple analysis showing that competition between vortex shedding and cylinder oscillation frequencies give rise to observed beating phenomena.
Mixing Enhancement of Non-Newtonian Fluids Using Unconventional Configurations
Authors: Ascanio Gabriel , Brito-Baza´n Magdalena , Brito-De La Fuente Edmundo , Carreau Pierre J. , Tanguy Philippe A.
Published: March 2009

Dynamic perturbations and off-centered single impeller configurations have been investigated to reduce mixing time with shear thinning fluids. The use of a color-decolorization technique based on a fast acid-base reaction allowed to measure mixing times and to reveal the presence of both segregated and dead zones. A statistical design approach has been used to evaluate the effect of the impeller position as well as the dynamic conditions and their interactions. Mixing times and flow patterns for shear thinning fluids were presented and compared to conventional operating modes. Homogenization was significantly enhanced when a radial flow impeller was used under both off-centered and dynamic perturbation conditions. In the case of an axial flow impeller, a combination of a large axial displacement with long clockwise times and short counter-clockwise times gave better mixing times.
Applying the Galerkin Least Squares Finite Element Method for Solving Stirred Tank Velocity Fields
Authors: Bittorf Kevin J.
Published: March 2009

The Galerkin Least Squares finite element solver, in conjunction with the Spalart-Allmaras turbulence closure model, is used to solve the RANS based equations for flow fields in stirred tank reactors. This GLS finite element method is well established in the aerospace industry and presently is being validated for flow fields used in industrial processes that are commonly found in the pharmaceutical, chemical, food, and personal products industries. The CFD results, computed in the commercial package ORCA, compared well with experimental data attained for the dominating macro flow structures in an axial and radial impeller stirred tanks. The CFD quantitatively predicts the two and three-dimensional wall jet structures that govern the bulk flow in a stirred tank and are responsible for blending, solid suspension, and macro-flow. This area of experimentation provides an initial basis for CFD validation for bulk flows in stirred tank reactors.
The Application of Submerged Jets to the Mixing of Slurries
Authors: Hammad Khaled J.
Published: March 2009

The ongoing cleanup effort at various DOE radioactive waste storage sites heavily relies on submerged jets during the mobilization and mixing phase of the settled sludges. Mobilization and mixing of the waste is a prerequisite for retrieval and transport to separation and processing facilities. The present study attempts to provide an insight into the flow conditions existing during the deployment of submerged jets to create uniform slurry conditions. Simulations that emulate the rheological characteristics of the waste mixture during mobilization are carried out. A particular attention is paid to how a non-Newtonian rheology affects the growth rate and mixing ability of the submerged jets.
Chaotic Mixing in Time-Periodic 3-D Flows
Authors: Rodrigo A. J. S. , Mota J. P. B. , Saatdjian E.
Published: March 2009

Mixing in a special class of three-dimensional, non-inertial time-periodic flows is studied quantitatively. In the type of flow considered here, the cross-sectional velocity components are independent of the axial flow which is assumed to be fully developed. Using the eccentric helical annular mixer as a prototype, the time-periodic flow field is induced by adding a sinusoidal component to the rotation speed of the inner cylinder. For a given 3-D mixer geometry, the degree of mixing achieved is a function of two parameters that measure the strength of the cross-sectional stirring protocol relative to the mean residence time of the fluid in the mixer: the average number of turns of the outer cylinder, and the average number of modulation periods. We find that for a given mixer geometry and mean residence time, there is an optimum modulation frequency for which the standard deviation of the temperature field at the exit is a minimum.
Multi-Dimensional Numerical Simulation of Burnout on Horizontal Surface in Pool Boiling
Authors: Stosic Zoran V. , Stevanovic Vladimir D.
Published: March 2009

Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed under high heat fluxes, near to and at the occurrence of burnout conditions. Heat flux through the vessel bottom wall is varied and its influence on the pool boiling dynamics is analysed. Dynamics of vapour generation on the heating wall is modelled through the density of nucleation sites and the bubble residence time on the wall. The nucleation sites are determined by a random function. The applied numerical grid is able to represent the nucleation sites on the heating wall for both fresh (polished) and aged (rough) heaters at the atmospheric pool boiling conditions. Results are presented for short time period after the initiation of heat supply and vapour generation on the heating surface, as well as for quasi steady-state conditions after two seconds from pool boiling initiation. The results show a replenishment of the heating surface with water and partial surface wetting for lower heat fluxes, while heating surface dry-out is predicted for high heat fluxes. The influence of the density of nucleation sites and the bubble residence time on the wall on the pool boiling dynamics is investigated. Numerical simulations show that decrease of the density of nucleation sites and increase of bubble residence time on the heating surface (characteristics pertinent to fresh-polished heaters) lead to the reduction of critical heat flux values. Obtained results are in excellent agreement with the recent experimental investigations of the upward facing burnout conditions on the horizontal heated plate. Details of the developed numerical procedure are presented. The introduced method of random spatial and temporal generation of the vapour at the heated wall is a new approach. It enables the macroscopic representation of the population of microscopic vapour bubbles, which are generated at nucleation sites on the heater wall, and which burst through liquid micro-layer in thermal-hydraulic conditions close to the burnout. The applied numerical and modelling method has shown robustness by allowing stable calculations for wide ranges of applied modelling boiling parameters (density of nucleation sites and bubble residence time).
Examination of Welding Nozzle Jet Flow at Cold Flow Conditions
Authors: Orakwe P. A. , Johnson D. A. , Weckman E. J.
Published: March 2009

A fundamental study of welding nozzle flow under cold flow conditions is presented. The aim is to examine the shielding gas flow characteristics for several Gas Metal Arc Welding (GMAW) flow conditions. Experimental investigations and numerical modeling are used to predict the flow behaviour of the gas shielding the weld pool. Results are presented for generic GMAW nozzle configurations at typical welding situations under cold flow. Flow visualization and Particle Image Velocimetry (PIV) reveal the various flow characteristics that are crucial to optimization of weld pool protection by the shielding gas. Numerical modeling of the flow is performed at conditions similar to the PIV experiments using the k-ε turbulence model in a commercial CFD package. Numerical predictions of the mean velocities agree reasonably well with PIV experiments, particularly in the radial wall jet region of the flow field. However, the turbulent kinetic energy is greatly over-predicted due to the eddy-viscosity stress-strain approximation in the k-ε model.
Teaching Advanced Fluids Engineering and CFD
Authors: Stubley Gordon D.
Published: March 2009

As CFD technology matures, there is increasing need for undergraduate CFD education. CFD allows the undergraduate student to calculate flow features that are beyond the scope of concepts covered in introductory courses. In this paper it is shown how the teaching of CFD and fluid mechanics can be integrated in a senior level course to develop professional practitioners of CFD. The course uses techniques like CFD visualization and a case study approach to reinforce student understanding of physical features of complex fluid flows. Full advantage is taken of the physical basis of the finite volume method to connect the structure of discrete equation sets, solution accuracy and iterative convergence trends to the features of simulated flows. The success that students achieve in developing and integrating CFD and fluid mechanics knowledge is measured in a final project in which CFD is used to evaluate a proposed design change.
Optimization of a Liquid Lead-Bismuth Eutectic Spallation Target Using Computational Fluid Dynamics
Authors: Pointer David , Sofu Tanju , Gohar Yousry
Published: March 2009

A liquid Lead-Bismuth Eutectic (LBE) spallation target has been developed for the subcritical multiplier (SCM) station of the Accelerator-Driven Test Facility (ADTF). Target design objectives and constraints were defined and utilized to satisfy the engineering requirements and to minimize the design development time and cost. Physics, heat transfer, hydraulics, structural, radiological and safety analyses were iterated to arrive at the final design concept. The optimization of the thermal hydraulic characteristics of the target concept through the parametric evaluation of multiple design alternatives using Computational Fluid Dynamics (CFD) to predict fluid dynamics and heat transfer behaviors is described in this paper.
Numerical Analysis of Three-Dimensional Flow in an Industry-Size Hydrothermal Autoclave Subjected to Non-Uniform Heating
Authors: Li Hongmin , Wang Guo-Xiang , Evans Edward A.
Published: March 2009

Hydrothermal growth is an important industrial process to produce piezoelectric crystals such as quartz. It takes place in a cylindrical container called an autoclave, which is filled with aqueous solution at a high temperature and a high pressure. The high temperature growth condition is maintained through electrical resistors on the outer surface of an autoclave. In practice there is a non-uniform heating condition in the circumferential direction. Many theoretical and numerical studies, however, assume an axisymmetric heating condition. This paper presents a numerical analysis of the three-dimensional heat transfer and fluid flow in hydrothermal growth due to such non-uniform heating. The analysis is based on an industry-size autoclave with an aspect ratio of 10. The non-uniform heating is introduced on the surface of both the lower dissolving chamber and the upper growing chamber of an autoclave with and without a baffle at the middle height. The flow and isotherm patterns were obtained with the temperature difference between the two chambers kept at 10 °C. The circumferentially non-uniform temperature has dramatic effects on the three-dimensional flow and therefore the temperature distribution in the autoclave. When the dissolving chamber is subjected to circumferentially non-uniform heating, a baffle is essential to create a uniform growth environment in the growing chamber. To obtain high quality single crystals, however, the temperature control on the growing chamber wall is more important than that on the dissolving chamber wall.
Simulation of OECD/NEA International Standard Problem No. 43 on Boron Mixing Transients in a Pressurized Water Reactor
Authors: Scheuerer Martina
Published: March 2009

The International Standard Problem, ISP 43, was defined by the OECD/NEA and the US NRC for the validation of three-dimensional Computational Fluid Dynamics (CFD) software. The underlying experiment was performed in the 2×4 Loop Facility of the University of Maryland, College Park, U.S.A (UMCP). The test facility is a scaled-down model of the Three Mile Island TMI-2 reactor with detailed reconstruction of the reactor pressure vessel (RPV). The ISP 43 experiments focussed on rapid boron dilution transients in the RPV cold leg and downcomer. The simulations of the ISP 43 were performed with the CFX-TASCflow software. Numerical errors were monitored by comparing results obtained with different higher order discretisation schemes. Uncertainties related to physical modelling, like buoyancy effects and reactor core models, were also investigated. The simulation results show good agreement with data and prove that CFD methods can be usefully applied to this class of nuclear reactor problems.
Investigation of Various Structure Identification Methods and the Effects of Tabs on the Near Field of Round Jets
Authors: Waterman S. , Holme T. , McIlwain S. , Pollard A.
Published: March 2009

The effects of various combinations of vortex-generating tabs on the turbulence structures in the near-field of a round jet are investigated using LES simulation and flow visualization techniques. The visualization methods include stream-wise and non-streamwise vorticity, and a variety of methods that use the invariant of the velocity gradient tensor (the discriminant, Q value and the second eigenvalue condition). Integration of the LES data sets suggest that the structural changes as a result of introducing tabs is significant; however, the methods used to deduce these changes are not always consistent with one another. In some cases, one scheme will produce large amounts of background “noise” while others are less prone to this effect. It is concluded that qualitatively, the four tab case produces the greatest amount of small scale structure.
Application of the POD to the Similarity Region of an Axisymmetric Turbulent Jet
Authors: Gamard Stephan , George William K.
Published: March 2009

Multipoint instantaneous measurements of the streamwise velocity component were obtained in the far field region of an axisymmetric turbulent jet from 20 to 69 diameters downstream for jet exit Reynolds numbers ranging from 40,000 to 84,700. The Proper Orthogonal Decomposition (POD) was then applied to a double Fourier transform in time and azimuthal direction of the two-point velocity correlation tensor. The first eigenspectrum, which contains more than 62% of the resolved streamwise energy, has two peaks: one at azimuthal mode-2 at near zero frequency, and another at mode-1 at a local Strouhal number (fx/Uc) of approximately 1. When checked against two-point statistics similarity analysis from Ewing (1995) extended to the POD, the results compare favorably and also give some hints into the resolution necessary to cover the field.
Vortices Within the Flow Separation in a Decelerating Channel Flow: Time-Averaged Characteristics
Authors: Kinoue Y. , Setoguchi T. , Kaneko K. , Murasaki T. , Inoue M.
Published: March 2009

An experimental equipment for studying the vortex behavior in 3D flow separation was constructed to have a comprehensive understanding of a separated channel flow. The separation occurs on three side walls of the straight channel by the suction from a porous side wall. Several types of separation can be generated by changing the sucked flow rate and providing the inlet flow with velocity gradient. For a strong decelerating-flow without the inlet velocity gradient, an alternate flow pattern with an opposite vortex occurs at considerably irregular intervals. With the inlet velocity gradient, a vortex appears and disappears along an inclined separation line for a moderate decelerating-flow, and a large stable vortex exists in the separation region for a strong decelerating-flow. The behavior of these vortices was examined and discussed in relation to the vortices including in the inlet flow.
Stochastic Estimation and Non-Linear Wall-Pressure Sources in a Separating/Reattaching Flow
Authors: Naguib A. , Hudy L. , Humphreys W. M.
Published: March 2009

Simultaneous wall-pressure and PIV measurements are used to study the conditional flow field associated with surface-pressure generation in a separating/reattaching flow established over a fence-with-splitter-plate geometry. The conditional flow field is captured using linear and quadratic stochastic estimation based on the occurrence of positive and negative pressure events in the vicinity of the mean reattachment location. The results shed light on the dominant flow structures associated with significant wall-pressure generation. Furthermore, analysis based on the individual terms in the stochastic estimation expansion shows that both the linear and non-linear flow sources of the coherent (conditional) velocity field are equally important contributors to the generation of the conditional surface pressure.
The Three-Dimensional Evolution of the Large-Scale Structures in the Impinging Round Jet
Authors: Hall J. W. , Gao N. , Ewing D.
Published: March 2009

The evolution of the large-scale structures in the impinging round jet were studied by measuring the fluctuating pressure on the impingement surface for nozzle-to-plate distances of 2.0, 3.0 and 4.0 nozzle diameters. It is found that the large-scale vortex ring structures played a much more dominant role when the nozzle-to-plate spacing was 2.0 diameters than for either 3.0 or 4.0 diameters. The results for a nozzle-to-plate spacing of 3.0 nozzle diameters more closely resembles the spacing of 4.0 diameters. The convection velocity of the different azimuthal modes were deduced from radial cross-spectra measurements. It was found that the convection velocity of all the azimuthal modes were similar and the convection speed for the structures measured with the fluctuating pressure were independent of nozzle-to-plate distance.
Experimental Study of Aeroacoustics in Supersonic Nozzles
Authors: Okamoto Kei , Shimura Kazuyasu
Published: March 2009

In supersonic nozzles, changing pressure ratio varies not only flow conditions but also noises. In order to clarify the relationships between noises and flows (such as shock waves and separation), the present study was conducted using the Fourier Analysis of aerodynamic noises and the Schlieren method. From the investigation, it was found that when the flow was separated from one side of the nozzle, the peak of the spectrum of the frequency response was at around 2000Hz. However, when the flow was in the whole area, the peak of the spectrum was at around 5000Hz.
An LDV Study of the Influence of the Radiator on a Cooling Module Fan
Authors: Martinuzzi Robert J. , Kopp Gregory A. , Havel Brian
Published: March 2009

The influence of the radiator on the flow through an automotive cooling fan module was investigated using Laser Doppler Velocimetry for three different flow conditions. It is found that at the nominal design point, the radiator acts as an effective flow straightener. At low flow rates, fan induced pre-swirl is significant, but the radiator helps reduce reverse flow through the fan. Under ram air conditions the upstream inlet distortions persist through the module resulting in a highly distorted outlet flow.
Three-Dimensional Bubble Reconstruction in a Pipe Flow Using Shadow Technique
Authors: Ortiz-Villafuerte Javier , Hassan Yassin A. , Furukawa Toru
Published: March 2009

Two different three-dimensional reconstruction techniques for the shape of gas bubbles flowing in a liquid are presented. The first technique is based on the Dynamic Generalized Hough Transform Algorithm, and the second on the Metaball Model. These techniques are suitable for analysis of turbulent two-phase bubbly flows. Both techniques require at least two views of the bubble intended for three-dimensional reconstruction, and can be used in either stereoscopic or orthogonal camera setups. Once the reconstruction is accomplished, the bubble images can be accurately removed from the images acquired during Particle Image Velocimtery or Shadow Image Velocimetry measurements. After removing the bubble images from PIV images, a typical analysis of the liquid phase can be performed. This improves the accuracy of the statistical analysis of the parameters of each phase.
Processing of Metal Matrix Composites: Bidimensional Numerical Model of the Infiltration of Fibrous Preform by a Pure Metal
Authors: Lacoste E. , Del Borrello C. , Mantaux O. , Danis M.
Published: March 2009

The infiltration process is one of the techniques employed to work out polymer matrix composites (PMC) or metal matrix composites (MMC) and with continuous reinforcement. It consists in injecting the liquid (resin or metal) through a fibrous reinforcement placed in a mould. In the case of the MMC, the fibres and the mould are initially preheated at temperatures lower than the temperature of metal solidification. These thermal conditions induce phenomena of phase change of metal when the metal is in contact with the fibres. These phenomena disturb the flow of metal through the fibrous network. In order to follow the displacement of metal in the preform and take into account of the phase change, a two-dimensional numerical model based on a finite volume formulation was developed, on a very simple geometry.
CFD Simulations and Experimental Study of Two-Phase Flow in Sand Coremaking Process
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: March 2009

The results of an experimental study and 3D numerical simulations of resin bonded sand/air flow in a square corebox with an H-shape insertion and passage between upper and lower pockets of the pattern are presented. A computer controlled electronic system was designed and built to measure pressures and flow rates inside the corebox during mold filling, gassing and purging cycles of Phenolic Urethane Amine (PUA) process. Contour maps of the pressure distributions inside the corebox were created based on barometric measurements. A good agreement between experimental results and numerical simulations was found.
Instability and Transition of a Plane Bubble Plume
Authors: Caballina Ophe´lie , Climent Eric , Dusˇek Jan
Published: March 2009

When bubbles are continuously released from a located source at the bottom of a fluid layer initially at rest, a plume is produced. The motion of the carrier fluid is initiated and driven by buoyancy of the bubble cloud. In the present study, a detailed analysis of the bubble plume transition is investigated. The continuous phase flow is obtained by direct numerical resolution of Navier-Stokes equations forced by the presence of bubbles. Collective effects induced by the presence of bubbles are modelled by a spatio-temporal distribution of momentum. Time evolution of the dispersed phase is solved by lagrangian tracking of all the bubbles. Focused on the description of plume transition, several configurations (plume widths, fluid viscosity, injection rate) are investigated. During the laminar ascension of the plume, fluid velocity profiles can be non-dimensionalised on a single auto-similar evolution. Dimensional analysis provides a prediction of the limit rising velocity of the plume top. This prediction has been confirmed by our numerical simulations. Furthermore, our first results point out the symmetry breaking induced by plume instability which appears beyond a critical transition height. Various data show that the Grashof number based on injection conditions is the key parameter to predict the transition of the plume. Our results agree very well with recent experimental data. Comparison with experiments on thermal plumes in air shows that the bubble plume is more unstable. This feature should be related to the lack of diffusion in the lagrangian transport of density gradient by the bubble cloud and to the slip velocity between the two phases.
A Parallel Domain Decomposition Technique for Meshless Methods Applications to Large-Scale Heat Transfer Problems
Authors: Divo Eduardo , Kassab Alain J. , Mitteff Eric , Quintana Luis
Published: March 2009

Mesh reduction methods such as the boundary element methods, method of fundamental solutions or the so-called meshless methods all lead to fully populated matrices. This poses serious challenges for large-scale three-dimensional problems due to storage requirements and iterative solution of a large set of non-symmetric equations. Researchers have developed several approaches to address this issue including the class of fast-multipole techniques, use of wavelet transforms, and matrix decomposition. In this paper, we develop a domain-decomposition, or the artificial sub-sectioning technique, along with a region-by-region iteration algorithm particularly tailored for parallel computation to address the coefficient matrix issue. The meshless method we employ is based on expansions using radial basis functions (RBFs). An efficient physically-based procedure provides an effective initial guess of the temperatures along the sub-domain interfaces. The iteration process converges very efficiently, offers substantial savings in memory, and features superior computational efficiency. The meshless iterative domain decomposition technique is ideally suited for parallel computation. We discuss its implementation under MPI standards on a small Windows XP PC cluster. Numerical results reveal the domain decomposition meshless methods produce accurate temperature predictions while requiring a much-reduced effort in problem preparation in comparison to other traditional numerical methods.
A New Design to the Compressed Air Engine
Authors: Jandhyala Aditya Srujan , Varun G. S. , Paliwal Richa
Published: March 2009

Compressed air is a potential energy source which has been widely used in high pressure operations, using compressed air as an alternative for fuel gives a powerful new dimension for eco friendly engines. A compressed air engine works similar to the working of a compression ignition engine. On using a single cylinder engine, the four strokes of a compression ignition engine are simulated. At the end of the compression stroke, air from the compressor is directly injected into the cylinder where air is already present at a compressed state. The air compressed in the cylinder is at a much higher temperature, in the range of about 300–400 degrees Celsius (depending on the compression ratio), than the compressed air from the compressor which is at room temperature, thus causing a difference of temperatures. The mixture trying to attain a common temperature due to expansion, thrusts onto the piston head, hence gives the required power to the engine.
Modelling of Slurry-Handling Piping Element Under Interference Conditions
Authors: Chand Prem , Rajulu K. Govinda , Reddy Y. Krishna
Published: March 2009

The paper presents a new approach to predict the two-phase performance of jet-pumps under interference conditions. We limit our study mainly to diffuser and transport regions of the jet pump. The five essential pre-requisites which form the backbone of our approach are a fairly generalized and accurate approach to (i) solid-fluid interaction, (ii) particle diffusion under generalized flow field, (iii) friction factor-Reynolds number equation, (iv) solid-fluid flow through ducts and (v) mixing of primary and secondary jets using the approach of Wang et al. [1] based on boundary layer concept. The extensive experimental data of several research workers along with fresh data generated on specially designed test-rig support the new approach.
A CFD Study to Analyze the Aerodynamic Torque, Lift, and Drag Forces for a Butterfly Valve in the Mid-Stroke Position
Authors: Leutwyler Zachary , Dalton Charles
Published: March 2009

The ability to accurately predict the aerodynamic torque and lift and drag forces on a two-dimensional model of a 0.18 aspect ratio biconvex circular-arc disc operating in a compressible flow using Fluent 6.0 was investigated. Grid-convergence and time-convergence/stability were analyzed first, followed by a qualitative study of the Spalart-Allmaras, k-ε, and k-ω turbulence models with their enhancement features and model variants. Fluent was used to predict the pressure profile on the disc surface for disc positions 30°, 45°, and 60° (where 0° is the fully closed position), and over a range of pressure ratios. The pressure ratios were selected to determine the capability of Fluent to accurately predict the flow field and resulting torque in flows ranging from nearly incompressible to highly compressible. Fluent predictions for the pressure profiles on the disc were compared to test data so that the lift and drag forces and aerodynamic torque could be determined responsibly. Acceptable comparisons were noted.