bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of the Effective Tensile Strength of Newtonian and Non-Newtonian Fluids Under Dynamic Stressing
Authors: Williams P. Rhodri , Williams Rhodri L. , Brown Stephen W. J.
Published: March 2009

The ‘Bullet-Piston’ (B-P) dynamic stressing technique has been used to study the tensile strength, Fc, of Newtonian and non-Newtonian fluids. A comparative study of the effects of viscosity on Fc for silicone oils (Newtonian) and aqueous polyacrylamide (PAA) solutions (non-Newtonian) was made. Both systems exhibited a power law dependency of the form Fc ∝ µn, where µ is the viscosity and n is the power index. For the Newtonian system, n was found to be 0.09 in close agreement with the findings of Couzens and Trevena (1974) for silicone oils whilst a value of 0.16 was found for the PAA solutions.
Stabilization of Solution to Navier-Stokes Equations by Feedback Control Defined on the Boundary
Authors: Fursikov Andrei V.
Published: March 2009

Let vˆ be a velocity vector field of steady-state fluid flow in a bounded container. We do not suppose that vˆ is stable. For each fluid flow which is close to vˆ at time moment t = 0 we propose a mathematical construction of feedback control from the boundary of the container which stabilize to vˆ this flow, i.e. which forces this flow to tend to vˆ with prescribed exponential rate. We introduce a notion of “real process” which is an abstract analog of fluid flow or (in other version) of numerical solution of Navier-Stokes equations. Real process differs from exact solution of three-dimensional Navier-Stokes equaitons on some small fluctuatons. Alhtough construction of feedback control is based on precise solving of Navier-Stokes equations, feedback control obtained by this method can react on unpredictable fluctuations mentioned above damping them. Such construction can be useful for numerical calculation because there fluctuations appear always.
A Model of Coherent Disturbances in Compressible Mixing Layers
Authors: Yang Hong , Tumin Anatoli
Published: March 2009

A theoretical model of harmonic perturbations in a compressible turbulent mixing layer is proposed. The model is based on the triple decomposition method. It is assumed that the instantaneous velocities, temperature, and pressure consist of three distinctive components: mean (time-averaged), coherent (phase-averaged), and random (turbulent) motion. The interaction between incoherent turbulent fluctuations and large-scale coherent disturbances is incorporated by the Newtonian eddy viscosity model. The governing equations for the coherent disturbances have the same form as in laminar flow with substitution of the Reynolds number and the Prandtl number by their turbulent counterparts. A slight divergence of the flow is also taken into account. Theoretical results and comparison with experimental data reveal the significance of interaction between the coherent and random constituents of the flow.
Towards a Greater Understanding of Turbulent Skin-Friction Reduction
Authors: Hutchins Nick , Choi Kwing-So
Published: March 2009

Measurements have been made in a turbulent boundary layer modified by flow aligned vertical (sub-boundary layer) elements. Comparisons between the coherent structure (near-wall and outer-layer region) for both modified and canonical cases have been conducted in order to better understand the mechanism of skin friction reduction. Thus far we can report a modified near-wall convection velocity obeying inner scaling and a reduced spread of correlated events away from the wall. The outer-layer appears to be characterised by large-scale arch-like structures which produce a velocity field consistent with the heads of lifted near-wall horseshoe vortices. The modified case shows reduced convection velocity, increased frequency of occurrence and increased entrainment for this type of outer-layer event.
Experimental Investigation of Turbulent Flow With Separation Over a NACA 4412 Airfoil at Angle of Attack 20 Degree
Authors: Badran Omar O. , Bruun Hans H.
Published: March 2009

This paper presents the measured mean flow and Reynolds stresses results, obtained on the center-line plane of the airfoil, covering the boundary layers over the upper surface, the potential flow region and the wake downstream of the trailing edge, at αa = 20°. The flying X-hot-wire probe was used to measure mean velocity and turbulence structure over the airfoil. An improved understanding of the physical characteristics of separation on the airfoil sections and in the region of the trailing edge is of direct value for the improvement of high lift wings for aircraft. From the study of the separation flow at angle of attack αa = 20°, the following can be concluded: A stable separation bubble has developed near the trailing edge of the airfoil, covering around 0.6c of the airfoil surface. Also it is found that values of the Reynolds normal and shear stresses move away from the surface with downstream distance, showing turbulence diffusion to be more evident in this flow. In the wake region, relatively large values of Reynolds stresses occurred, which were related to the vertical oscillations in the upper wake.
Surface Tension Measurement at High Pressure
Authors: Dechoz Je´roˆme , Roze´ Claude
Published: March 2009

A non-intrusive method, based on the properties of capillary waves, is used to measure surface tension at high pressure. Results are given for diesel fuel, gasoline and n-heptane. Large variations with pressure are showed. A model is proposed to understand the influence of pressure upon the liquid-gas interface. Results of both approaches are in good agreement.
Real-Time In-Situ Measurement of Slurry Concentration Distribution in Tanks
Authors: Bamberger Judith Ann
Published: March 2009

Ultrasonic signals are well suited for characterization of multiphase fluid properties and flows. The signals are not degraded by noisy process conditions, can penetrate vessel and piping walls, and can be used to interrogate fluids and dense opaque suspensions. This paper presents a simple ultrasonic measurement application that shows the ability of ultrasonic sensors to measure slurry concentration during slurry mixing in tanks. Results from two experiments show the use of real-time measurements of ultrasonic signal attenuation to track the process of slurry mixing in situ and to track the ability to maintain a well mixed steady state condition. Comparison of means of the ultrasonic measurements with means obtained from discrete extractive measurements show that the distributions overlap and cannot be statistically distinguished.
Non-Steady Three-Dimensional Flow Field Analysis in Supersonic Flow Induction
Authors: Alhussan Khaled , Garris Charles
Published: March 2009

In this paper, supersonic pressure-exchange ejectors were studied through numerical analysis, CFD modelling. The critical role played by the geometry on ejector performance was clearly established. CFD simulations (3D) are capable of predicting all trends in the performance curves. Results show the effect that non-steady flow can achieve over the steady flow ejector.
Experimental Study of a Normal Shock/Homogeneous Turbulence Interaction
Authors: Auvity Bruno , Barre Ste´phane , Bonnet Jean-Paul
Published: March 2009

The problem of shock wave–turbulence interaction is addressed experimentally in a simplified flow configuration: the shock is normal to the flow direction and the incoming turbulence is homogeneous and quasi-isotropic. This paper mainly deals with the problem of the experimental realization of such an interaction in a supersonic wind tunnel. On the basis of an experimental set-up that showed great aptitude in creating a shock-turbulence interaction pure from major parasitic effects, see Barre et al. (1996), a new turbulence generator and a new shock generator were designed and built. It was found that the new turbulence generator creates a homogenous and quasi-isotropic turbulent supersonic flow at a distance of about 25 mesh sizes. The benefit of this new system was to increase the turbulence level before the interaction with the shock from 0.3% to 1.7%. The new shock generator system permitted to stabilize a normal shock of larger size compared to the previous configuration, at a distance of 32 mesh sizes. Initial conditions at the shock position were determined with details: important turbulent quantities of the supersonic flow before the interaction, such as turbulent kinetic energy, dissipation rate, Taylor micro-scale and integral length scale, were estimated. With this new experimental set-up, detailed turbulence measurements before and after the shock using fluctuations diagram techniques will be performed.
Pitched and Yawed Circular Jets in Cross-Flow
Authors: Milanovic Ivana M. , Zaman K. B. M. Q.
Published: March 2009

Results from an experimental investigation of flow field generated by pitched and yawed jets discharging from a flat plate into a cross-flow are presented. The circular jet was pitched at α = 20° and 45° and yawed between β = 0° and 90° in increments of 15°. The measurements were performed with two X-wires providing all three components of velocity and turbulence intensity. These data were obtained at downstream locations of x = 3, 5, 10 and 20, where the distance x, normalized by the jet diameter, is measured from the center of the orifice. Data for all configurations were acquired at a momentum-flux ratio J = 8. Additionally, for selected angles and locations, surveys were conducted for J = 1.5, 4, and 20. As expected, the jet penetration is found to be higher at larger α. With increasing β the jet spreads more. The rate of reduction of peak streamwise vorticity, ωxmax, with the downstream distance is significantly lessened at higher β but is found to be practically independent of α. Thus, at the farthest measurement station x = 20, ωxmax is about five times larger for β = 75° compared to the levels at β = 0°. Streamwise velocity within the jet-vortex structure is found to depend on the parameter J. At J = 1.5 and 4, ‘wake-like’ velocity profiles are observed. In comparison, a ‘jet-like’ overshoot is present at higher J.
Numerical Simulation of Three-Dimensional Separated Flow and Heat Transfer in a Sudden-Expansion Channel
Authors: Ota Terukazu , Mori Masafumi , Yoshikawa Hiroyuki
Published: March 2009

Numerical results of three-dimensional laminar separated and reattached flow and heat transfer in a suddenly-expanded rectangular channel are presented in this paper. Numerical calculations of Navier-Stokes equations and energy one are carried out using the finite difference method for three aspect ratios of 1.0, 2.0 and 4.0 at Reynolds numbers from 100 to 500. It is found that streamwise vortex pairs are generated, and their induced velocities shrink the major axis side of core flow, bringing about the flow toward the channel center line. Further, the minor axis moves outward as carrying the core fluid. Heat transfer mechanism in these mixing processes of flow is clarified.
Application of CFD Methods for the Simulation of the Flow Through a Filter in Dependency of the Operating Time
Authors: Cagna M. , Boehle M.
Published: March 2009

Filters are playing an important role in process engineering, chemical engineering as well as in many machineries like gas turbines, air conditioners or cars. At present it is possible to calculate the flow through a filter and predict the average pressure loss of the flow for the initial state of the filter medium. In the present paper a pragmatic procedure is introduced, which makes it possible to consider the deposition of dust onto the filter and the influence on the flow implied with it. For the application of the method the commercial CFD-Code FLUENT is used. The reasonability of the concept is shown by regarding the characteristic time scales of the flow and the dust deposition. The method is used to simulate the flow through a filter within a quadratic tube in dependence of the operating time.
Relationship Between Temperature Distribution and 2D Image of Condensation Jets Using Discrete Wavelets Multiresolution
Authors: Kimura Motoaki , Takei Masahiro , Saima Atushi , Vierow Karen , Saito Yoshifuru , Horii Kiyoshi
Published: March 2009

This paper describes the application of discrete wavelet transforms to the analysis of condensation jets in order to clarify the associated fluid and heat transfer phenomena. An experimentally obtained, two-dimensional image of the condensation particle density around the jet was decomposed into 7 levels of resolution with their respective wavelengths. Based on the known physical characteristics of turbulent flow around the jet, levels 0 and 1 were shown to represent the steady components of the condensation particle density and the higher levels represent the fluctuating components. From the analysis images, the width of the condensation zone was obtained and this compared well with the width inferred from temperature measurements. Thus, the method was verified and also provided data not available experimentally.
Wavelet Analysis of Memory Effects on Turbulence Structures in a Far Wake
Authors: Li Hui , Zhou Yu , Takei Masahiro , Saito Yoshifuru , Horii Kiyoshi
Published: March 2009

Initial condition effects in a self-preserving plane wake were investigated for two wake generators, i.e. a triangular cylinder and a screen of 50% solidity. Two orthogonal arrays of sixteen X-wires, eight in the (x, y)-plane, i.e. the plane of mean shear, and eight in the (x, z)-plane, which is parallel to both the cylinder axis and the streamwise direction, are used to simultaneously obtain velocity data in the experimental investigation. Measurements were made at x/h (x is the streamwise distance downstream of the cylinder and h is the height of the wake generator) = 330 for the triangular cylinder and 220 for the screen. A two-dimensional orthogonal wavelet transform is used to analyze the measured hot-wire data. This technique enables the turbulence structures of various scales to be separated and characterized. Discernible differences are observed between the two wake generators in the turbulence structures of large- down to intermediate-scales. The differences are quantified in terms of the Reynolds shear stress, kinetic energy and root mean square vorticity values.
3D Wavelet Multiresolution of Multiphase Flow CT Images
Authors: Takei Masahiro , Li Hui , Ochi Mitsuaki , Saito Yoshifuru , Horii Kiyoshi
Published: March 2009

The extraction of dominant particle density fluctuation in various time-space frequency levels on a pipeline cross section was performed using capacitance-computed tomography and three-dimensional discrete wavelets transform. As a result, particle density fluctuation downstream of a bent pipe is decomposed into the time-space levels in a non-choking state and a pseudo-choking state. The proposed method enables realization of the time and position at which particle density fluctuations with respect to dominant time-space levels pass through the pipeline.
Numerical Calculation of the Flow Field in Bubble Columns Using a Simplified Form of the Population Balance Equation
Authors: Wiemann D. , Lehr F. , Mewes D.
Published: March 2009

The three dimensional velocity field is numerically calculated for bubble columns using an Euler-Euler approach with an additional transport equation for the interfacial area. The spacial bubble number density is obtained by solving the population balance equation numerically. In order to reduce the numerical effort or to avoid restrictive assumptions for bubble break-up and coalescene processes a partial solution of the population balance is derived. It is valid asymptotically as the bubble swarm moves away from the distributor. The approximate solution leads to a transport equation for the mean bubble volume, which is solved in dependence of the bubble break-up and coalescence processes. Both phenomena are considered. For the numerical calculations the interfacial area transport equation is coupled with the balance equations for mass and momentum transport. The calculations are performed for instationary, three-dimensional flows in cylindrical bubble columns with diameters up to 0.29 m and 4.425 m of height.
Numerical Treatment of the Stress Jump Interface Condition for Laminar Flow in a Channel Partially Filled With a Porous Material
Authors: de Lemos Marcelo J. S. , da Silva Renato Alves
Published: March 2009

A number of natural and engineering systems can be characterized by some sort of porous structure through which a working fluid permeates. Boundary layers over tropical forests and spreading of chemical contaminants through underground water reservoirs are examples of important environmental flows that can benefit form appropriate mathematical treatment. 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 stresses at both sides of the interface are not of the same value. The objective of this paper is to present a numerical implementation for solving such hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in laminar regime. One unique set of transport equations is applied to both regions. Numerical results are compared with available analytical solutions in the literature for two cases, namely, with and without the non-linear Forchheimer term. Results are presented for the mean velocity across both the porous structure and the clear region. The influence of medium properties, such as porosity and permeability, is discussed.
Volume Tracking on Triangular Meshes
Authors: Shahbazi Khosro , Paraschivoiu Marius , Mostaghimi Javad
Published: March 2009

This paper investigates a volume tracking algorithm on triangular meshes, associated with modeling free surface flow and multi phase flow on complex geometry. The volume tracking algorithm is divided into two main tasks. First, a piecewise linear reconstructing the interface is used to approximate the interface at each interfacial cell with a segment line. The convergence study of this approach reveals first order accuracy in reproducing a circular material distribution. Second, a Lagrangian time integration accompanied by a full remap is carried out in order to advect volume material in time. A circular material distribution is tested under simple translation and rotation. Visualization of results shows that the circular shape is conserved while first order accuracy is observed.
A Droplet Simulation on Motion Topology With Mass Transfer Using Moving Unstructured Mesh
Authors: Jung Rho-Taek , Sato Toru
Published: March 2009

A direct simulation code for a moving and dissolving droplet by using three-dimensional hybrid unstructured mesh was developed. The multi-phase flow field is discretised by a cell-centred finite volume ALE (arbitrary Lagrangian Eulerian) formulation. Based on the fractional step method, a semi-implicit scheme in time is used. Other numerical aspects of the present method are the method of Rhie and Chow (1983) for incompressibility, a third-order compact upwinding for convection term, and a second-order central difference for diffusion term. The mesh consists of tetrahedron prisms near interface for viscous boundary layer and tetrahedrons in the other part. The interface between the droplet and water moves along spines in the radial direction that satisfies its kinematic condition. The effect of interface tension is taken into account directly in solving the Poisson equation for pressure. This method is applied to the mass transfer from a rising droplet. The non-dimensional parameters to describe this phenomenon are the Schmidt number, the Reynolds number based on rise velocity and the Eo¨tvo¨s number relating the surface tension to the gravitational acceleration, and the Ohnesorge number relating the surface tension to viscous force. From the simulation results, we found that there are three regimes of the path topology of rising droplet, i.e. rectilinear, helical-zigzag and zigzag motion. These are categorized by the Reynolds and the Ohnesorge numbers. The mechanism of the trajectory morphology is elucidated by the relation to vertex shedding from the droplet.
Simulation of Multiphase Flows in Complex Geometry Using a Hybrid Method Combining the Multi-Fluid and the Volume-of-Fluid (VOF) Approaches
Authors: Han Jaehoon , Alajbegovic Ales
Published: March 2009

A computational method combining the multi-fluid and the Volume-of-Fluid (VOF) approaches is presented to simulate industrial multiphase flows in complex geometry. This method is particularly applicable for flows where well-defined interfaces between different phases/fluids co-exist with small-scale multiphase structures. The interfaces in relatively large scales (that can be accurately resolved on a computational mesh with a practical size) are tracked by the VOF method, whereas the small scale multiphase flow structures (that are too computationally expensive to be explicitly tracked by the VOF method) are accounted for by using the multi-fluid approach. In order to provide more computational flexibility, any two of the phases tracked by the multi-fluid approach can either have different velocities (two-fluid model) or share the same velocities (equilibrium model). The hybrid method presented here enables efficient simulation of complex flows with multiple phases/fluids on arbitrary-shaped unstructured meshes. It is fully implemented in the commercial CFD software, AVL FIRE/SWIFT. The governing equations are discretized based on a finite volume method (FVM) and the pressure field is obtained using the SIMPLE algorithm. The effect of surface tension is also included for the phases tracked by the VOF method using a Continuum Surface Force (CSF) model. Application to a well-established example of multiphase flow—a Taylor bubble rising inside a stagnant liquid—is presented to demonstrate the capability of the method.
Analysis of Turbulent Scales in Variable Density Jets Using Laser Anemometry Techniques
Authors: Boujemaa S. , Amielh M. , Gharbi A. , Anselmet F.
Published: March 2009

This experimental study is concerned with the effect of density variations on the development of a turbulent jet. Our interest concerns the large turbulent scales in order to understand how density variations affect these structures involved in the mixing process. The integral scale evolutions are estimated from laser velocimetry measurements (PIV or LDV). Comparisons between the results obtained in an air jet and a helium jet are given in the development zone (X/Dj < 20), so that the effect of strong density variations (ratio 1 to 7) on these scales is deduced.
Flow Behavior in the Dump Diffuser Combustor With a Split Flow Effects of Inclined Wall in a Sudden Expansion Region
Authors: Inoue Kousuke , Fukada Tomohiro , Shizawa Takaaki , Honami Shinji
Published: March 2009

Recent aero-engine combustors have been of a large flame dome. The combustor diffuser wit h deep flame dome results in the large total pressure loss. It is important to obtain both better aerodynamics performance of the total pressure and exhaust gas characteristics of NOx in the combustor. Installation of an inclined wall within the dump diffuser combustor with a split flow at the flame dome head is suggested in order to improve the aerodynamic performance. The cold flow experiment in a model channel of the combustor diffuser conducted by the Laser Doppler Velocimetry system shows that the inclined wall is effective in improvement of the diffuser performance regardless of the ratio of the split flow rate. The key technology factor of inclined wall installation is the selection of the throat area ratio between the inclined wall and the flame dome.
Centrifugal Compressor Aerodynamic Design of Marine Engine Turbocharger by Three Dimensional Numerical Simulation
Authors: Kim Hong-Won , Oh Kook-Taek , Ghal Sang-Hak , Ha Ji-Soo
Published: March 2009

For the centrifugal compressor aerodynamic design of a turbocharger, first of all, the works for system matching to the engine specification must be preceded. Then, mean line design together with performance prediction should be carried out for preliminary design. In the mean line prediction, a slip factor is adopted as a function of flow coefficient and geometry instead of Wiesner’s equation, and it is found that the predicted result of slip magnitude is more accurate than that of conventional slip factor. Also, three-dimensional blade profile shape is generated on the basis of the preliminary design. The Navier-Stokes Equation solver with a turbulent model is used to find whether three-dimensionally designed geometry is reasonable by analyzing loading distribution of the blade. By investigating diffuser flow field of the simulated result, the diffuser inlet and exit angles were modified for the flow to move smoothly along the diffuser geometry. Modified performance prediction results shows better than those of original specification. Consequently, off design performance prediction results and numerical simulation result show good agreement with the experimental data. The modified design results show more increased compression ratio and efficiency than those of previous design results. The increased choke margin has made a stable operating range larger.
A Numerical Study on the Structure of Tip Clearance Flow in a Highly Forward-Swept Axial-Flow Fan
Authors: Lee Gong Hee , Baek Je Hyun
Published: March 2009

A three-dimensional Navier-Stokes analysis was performed to investigate the tip clearance flows in a highly forward-swept axial flow fan operating at design condition. The numerical solution was based on a fractional step method, and two-layer k-ε model was used to obtain the eddy viscosity. The tip leakage vortex decayed very quickly inside the blade passage and, thus, no distinct leakage vortex appeared behind trailing edge. The main reason was the severe decrease of the streamwise velocity of the vortex. Also the interaction of the vortex with the casing boundary layer and the through-flow were other possibilities of the fast decay of the vortex. Comparison between the numerical results and LDV measurements data indicated that the complex viscous flow patterns inside the tip region as well as the wake flow could be properly predicted, but more refinement in numerical aspects are needed.
Numerical Prediction of the Cavitation in Pumps
Authors: Dupont Philippe , Casartelli Ernesto
Published: March 2009

This paper presents a comparison between a coupled and a non-coupled approach for the prediction of the cavitation development in pumps. The coupling is defined here as the influence of the development of the cavitation on the main flow. Commercial CFD (computational fluid dynamic) software having a cavitation module and in-house developed code are used for this comparison. The intention of the authors is to evaluate these methods and their capabilities in predicting cavitating performance of pumps from an industrial point of view. In a first part, the two methods used are introduced and developed. In a second part, the results of these two approaches are compared for two impellers of the same specific speed having small geometrical differences leading to significant differences in the cavitation development. The ability and the benefits of the use of these different cavitation prediction approaches in the design process of a pump are finally discussed.
Computation of Flow and Heat Transfer in Turbine Blade Cooling Passages by Reynolds Stress Turbulence Model (Keynote Paper)
Authors: Chen Hamn-Ching , Han Je-Chin
Published: March 2009

Numerical predictions of three-dimensional flow and heat transfer are presented for non-rotating and rotating turbine blade cooling passages with or without the rib turbulators. A multi-block Reynolds-averaged Navier-Stokes method was employed in conjunction with a near-wall second-moment closure to provide detailed velocity, pressure, and temperature distributions as well as Reynolds stresses and turbulent heat fluxes in various cooling channel configurations. These numerical results were systematically evaluated to determine the effect of blade rotation, coolant-to-wall density ratio, rib shape, channel aspect ratio and channel orientation on the generation of flow turbulence and the enhancement of surface heat transfer in turbine blade cooling passages. The second-moment solutions show that the secondary flow induced by the angled ribs, centrifugal buoyancy, and Coriolis forces produced strong nonisotropic turbulent stresses and heat fluxes that significantly affected flow field and surface heat transfer coefficients.
Numerical Study on Tip Clearance Effect on Performance of a Centrifugal Compressor
Authors: Eum Hark-Jin , Kang Shin-Hyoung
Published: March 2009

Effects of tip clearance on through flows and performance of a centrifugal compressor impeller with six different tip clearances were numerically studied using CFX-TASCflow. The flow structures inside the impeller of a centrifugal compressor were visualized observing streamlines starting the leading edge of blade tips. The calculated results at the impeller exit were circumferential averaged for quantitative discussion. Flow, pressure and entropy contours at the impeller exit were largely influenced by the tip leakage flow. Tip clearance effect on the performance was decomposed into inviscid and viscous components using one-dimensional relations expressed in terms of the specific work reduction and the additional entropy generation. Both inviscid and viscous effects affected performance to similar extent, while efficiency drop was mainly influenced by viscous loss of the tip leakage flow. Performance reduction and efficiency drop due to tip clearance was proportional to the ratio of tip clearance to blade height. A simple model suggested in the present study predicts performance and efficiency drop quite successfully.
Computation of Axial Flow Compressor to Intake Flow Distortion
Authors: Ng Eddie Yin-Kwee , Liu Ningyu , Lim Hong Ngiap , Tan Tock Lip
Published: March 2009

The effects of the parameters of inlet distortions on the trend of downstream flow feature in axial compressor are simulated using an integral method. Other than the ratio of drag-to-lift coefficients of the blade and the angle of incidence, the value of distorted inlet velocity is found to be another essential parameter to control the distortion propagation. With this in mind, a distortion propagation line and corresponding distortion propagation factor are proposed to express the effect of the two main inlet parameters: the angle of incidence and the distorted inlet velocity, on the propagation of distortion. From the viewpoint of compressor efficiency, the distortion propagation is further described by a compressor critical performance. The results provide a physical insight of compressor axial behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the active role of compressor in determining the velocity distribution when compressor responds to an intake flow distortion.
Design of Generator Spline Retaining Ring With Low Windage Loss
Authors: Tong Wei
Published: March 2009

Retaining rings in a generator are used to constrain the centrifugal force of the field winding end turns. A conventional retaining ring may cause a high pressure drop at the stator-rotor gap entrance and thus result in a large windage loss. The present work relates to the design of a retaining ring with a spline profile near its inboard end to thereby improve the axial cooling flow fluidity and enhance generator cooling efficiency. By altering the outer profile of the retaining ring, it has been found that approximately 30–60% of the pressure drop across the stator-rotor gap entrance can be reduced. As a result, the overall generator efficiency may increase about 0.005–0.01%.
Interaction of Shock and Expansion Wave With Solid Particles in Supersonic Flows
Authors: Dolatabadi Ali , Mostaghimi Javad , Pershin Valerian
Published: March 2009

Interaction of solid particles with shock and expansions in supersonic flows is analyzed. In this analysis, a dense cloud of solid particulates is modeled by using a fully Eulerian approach. The dispersed flow and the gas flow were considered in the Eulerian frame whereby most of the physical aspects of the gas-particle flow can be incorporated. In addition to the momentum and energy exchanges in the form of source terms appearing in the governing equations, the two phases were strongly coupled by considering the volume fraction of the particulate phase in the equations. The simulation performed for a High Velocity Oxy-Fuel (HVOF) process under typical operating conditions in which the powder loading is high and the two-phase flow is not dilute near the injection port. The simulations showed large variations in the flow regime in the region that most of the particles exist. Unlike the results corresponding to the Lagrangian approach, the flow becomes subsonic near the centerline and the drag force decreases significantly since the relative Mach number is small. The validation experiments showed that the variation of flow regime by changing the relative Mach number could significantly change the particle drag force, and consequently process efficiency.
Analyses of Spatial CHF/Rewet Behaviour of Fuel Rod Bundle in Pump-Trip Simulation Experiment With Three-Dimensional Multi-Fluid Porous Media Approach
Authors: Stosic Zoran V. , Stevanovic Vladimir D. , Iguchi Tadashi
Published: March 2009

The investigation of three-dimensional transient propagations of dry-out fronts within a nuclear fuel rod bundle is performed, based on experimental and numerical simulations. The spreading of critical heat flux (CHF) fronts across a bundle, caused by gradual decrease of coolant mass flow rate without power increase is predicted, and the locus of dry patches is shown. Obtained results show that a simultaneous occurrence of CHF and rewet multi-fronts in simulated reactor coolant flow transient are less pronounced than in power transients. Due to a possible building of a vapour zone, the CHF front spatial propagation has to be carefully analysed in transient conditions.
Experimental and Numerical Study of Spray Ignition for In-Flight Re-Light
Authors: Lavergne K. , Quintilla V. , Lecourt R. , Lavergne G.
Published: March 2009

The context of this study is the prediction of re-ignition for turbojet engines after in-flight extinction at high altitude. Experiments have been performed on a simple geometry of a combustion chamber to test ignition at ambient conditions for three positions of the spark plug. Then, the two-phase flow corresponding to the experimental configuration has been simulated with the eulerian-lagrangian code used at ONERA. In parallel, a time dependent 0-dimensional model has been developed to predict the ignition of a cluster composed of fuel droplets when it is submitted to the spark inside the combustion chamber. This model has been applied on the two-phase flow computation in three elementary volumes located close to different spark plug positions. Ignition has been tested numerically for these clusters of drops, whose characteristics are dependent of their location in the combustion chamber, as well as, of the two-phase flow configuration in the geometry. Comparisons between experimental and numerical results are presented in this paper.
Solar Vehicles: The Challenge of Maximum Speed From Minimal Power
Authors: Watkins Simon , Humphris Clive
Published: March 2009

The World Solar Challenge is a race from Darwin to Adelaide which attracts purpose-built vehicles from around the world. Using only power from the sun, the vehicles reach speeds of over 100 km/hr and the current record holder averaged a speed of over 90 km/hr. In this paper the background to the race and some of the technology used is described. Since aerodynamic drag is the major resistance to motion, this is examined in detail, including the testing and design principles applied to the Australian “Aurora” vehicle which won the race in 1999 and came second in 2001. A highly efficient electric motor, developed specifically for the Aurora is also described.
Elliptic Relaxation of a Tensor Representation of the Pressure-Strain and Dissipation Rate
Authors: Carlson John R. , Gatski Thomas B.
Published: March 2009

A formulation to include the effects of wall-proximity in a second moment closure model is presented that utilizes a tensor representation for the redistribution term in the Reynolds stress equations. The wall-proximity effects are modeled through an elliptic relaxation process of the tensor expansion coefficients that properly accounts for both correlation length and time scales as the wall is approached. DNS data and Reynolds stress solutions using a full differential approach at channel Reynolds number of 590 are compared to the new model.
Computational Reconstruction of Fluctuating Flow Field in the Ocean
Authors: Sato Kei , Sato Toru
Published: March 2009

Two methods for computational reconstruction of fluctuating flows in the ocean based on field measurement data are suggested. Here full-3D treatment with the spatial scale of O(100m)–O(1000m) is taken into account. In the first method, the fluctuating flow based on measurement data is generated at inflow boundary and introduced into computational domain. In the second method, small wavenumber components of fluctuation in the ocean are forced in computational domain, and large wavenumber components are generated automatically. The results of each method are discussed with comparing with measured data, and effectiveness of each method is shown.
Alignment Trends of a Decomposed SGS Stress Tensor Determined From Holographic PIV Measurements
Authors: Tao Bo , Katz Joseph , Meneveau Charles
Published: March 2009

Based on the holographic PIV measurements in the core region of a square duct at ReH ≈ 1.2×105, the tensorial alignment of the deviatoric subgrid-scale (SGS) stress (τij) is shown to have a bi-modal behavior (Tao et al., 2001, 2002). To gain further insight into the statistical geometry of τij, we employ the Germano decomposition, τij = Lij + Cij + Rij (Leonard, 1974; Germano, 1986), and compute the decomposed stress elements directly from the velocity data. Their alignment trends are then investigated using joint probability density functions (pdf), similar to those in Tao et al. (2002). The alignment between the Leonard stress, Lij, and the filtered strain-rate (S˜ij) is found to exhibit a similar bi-modal trend, but the alignment angle between the corresponding eigenvectors is around 40° instead of 32°. The alignment between the SGS Reynolds stress, Rij and S˜ij, on the other hand, is found to be consistent with an eddy viscosity configuration. In contrast, the alignment between the cross stress, Cij, and S˜ij is more complicated and does not exhibit any significant trend. Furthermore, previously reported alignment trends of the vorticity vector, ω˜i, relative to τij, are primarily due to the contribution from Lij. The orientation of ω˜i relative to Cij shows less robust alignment trends, and there is no clear trend in the alignment of ω˜i relative to Rij.
Modelling of Compressibility Effects in Mixing Layer
Authors: Aupoix Bertrand
Published: March 2009

The ability of turbulence models to predict self-similar mixing layers is investigated. The influence of velocity is well captured but no model reproduces the sensitivity of the mixing layer to density differences. A correction proposed for boundary layer flows hardly affects mixing layer predictions. A correction is proposed but is not satisfactory. At last, compressible turbulence effects are investigated. Without corrections, models cannot predict the spreading rate reduction. Standard corrections predict too weak a reduction. The sonic eddy concept is validated whatever the turbulence model. A form suitable for Navier-Stokes codes is proposed.
Numerical Investigation on Vortex Shedding Flow Behind a Wedge
Authors: Djebedjian Berge
Published: March 2009

The present work is concerned with a numerical investigation of the unsteady two-dimensional incompressible turbulent flow around a 45° wedge inclined at an angle of attack of 45°. The incompressible time-dependent Navier-Stokes equations written in a finite volume formulation with an upwind discretization scheme were used in this study. The numerical solutions of the elliptic partial differential equations have been obtained using the standard k-ε turbulence model. The numerical results are compared with available experimental data. The comparison includes the Strouhal number and the distribution of velocities and vorticity in the wake flow. The comparison shows that the Strouhal number, time-averaged streamlines and vorticity pattern agree well with experiments. However, the agreement with the experimental data is less satisfactory for the time-averaged normal velocity profile and root mean square values of fluctuating velocity components.
Turbulent Flows in a Two-Dimensional 180° -Curved Diffuser With a Guide Vane
Authors: Mohamed Mohamed S.
Published: March 2009

Numerical and experimental investigations of the flow in a two-dimensional 180°-curved diffuser, with a guide vane interposed in the diffuser, is presented to clarify their characteristic and to improve the curved diffuser performance. Particular attention is focused on the effect of the variation in the interposed position of the guide vane on the flow field and pressure recovery. Measurements for mean longitudinal and transverse velocity profiles as well as the wall static pressure are performed at different downstream stations. Comparisons are made between the present measurements for the diffuser with a guide vane and without a guide vane [10]. The numerical investigation is based on the solution of the governing equations using a finite volume technique employing SIMPLE algorithm on co-located body-fitted grids. The two-equation model of turbulence, standard k-ε model, and the modified k-ε model [15] are employed in this investigation. The study indicated that the emerging velocity distribution is more uniform than that associated with flow in the diffuser without a guide vane. The presence of a guide vane is shown to suppress the formation of the region of flow separation, as a consequence, the performance of the diffuser is improved. The overall pressure recovery is 54% of the inlet dynamic pressure. The comparison between the numerical and experimental results indicates that the modified k-ε model satisfactorily predicts the overall characteristics of the flow in the diffuser. Numerical predictions show that the best position for a guide vane is positioning the vane towards the convex wall of the diffuser. Diffusers with a guide van at B/W1 = 0.25 to 0.333 give the highest-pressure recovery coefficient.
Effects of Applying a Stochastic Rebound Model in Erosion Prediction of Elbow and Plugged Tee
Authors: Chen Xianghui , McLaury Brenton S. , Shirazi Siamack A.
Published: March 2009

Solid particle erosion is a complex phenomenon that depends on many factors such as particle and fluid characteristics, type of material being eroded, and flow geometry. Fittings used in the oil and gas industry such as elbows are susceptible to erosion when solid particles are present in the flow. The momentum of particles carries them across streamlines and the particles impinge the outer wall of the elbow resulting in erosion damage. In an erosive environment, plugged tees are commonly used instead of elbows to reduce the erosion especially where space considerations are important and long-radius elbows can not be used. However, it is unclear how much of a reduction in erosion occurs by replacing an elbow with a plugged tee. In order to compare the erosion in an elbow and a plugged tee exposed to the same flow conditions, a CFD-based erosion prediction model is applied. The model has three primary steps: flow modeling, particle tracking, and applying erosion equations. The results from the model agree with experimental findings for the elbow geometry. However, the simulation results for erosion rate generated for the plugged tee requires a stochastic approach. Results obtained with the erosion prediction model before and after this modification are shown.
Laminar Flow Between Two Parallel Porous Walls With Variable Permeability and Wall Slip
Authors: Krishnambal S.
Published: March 2009

A class of exact solutions of two dimensional Navier-Stokes equations representing the flow between two porous parallel walls, when there exist variable suction and injection at the boundaries (with or with out slip) under the prescribed entry and outlet conditions at the ends of the channel of given length is obtained. These are exact solutions of the two dimensional Navier-Stokes equations for a suitable class of variable suction and injection prescribed at the walls. Certain interesting flow characteristics are observed, when analysed through the graphs of velocity profiles and stream lines. The change in the pattern of the stream lines corresponding to the various prescribed suction/injection velocities are observed. The convergence analysis (with slip) of the series solution is discussed with a suitable numerical example.
Velocity and Flow Rate Measurements in Capillaries With Arrays of Optical Fibres
Authors: Petrak Dieter , Niersmann Ulf
Published: March 2009

Results from the application of the spatial filtering velocimetry on capillary flow are presented. The type of the spatial filter is a differentail fibreoptical filter made by 16 step index fibres. Using tracer particles, the flow velocities along the capillary diameter and the volume flow were measured. The capillary is a transparent glass tube with inner diameter ranging from 0.15 mm to 0.5 mm. Using a gravitational measuring system the uncertainty of the flow measurement by the optical system was determined. For the laminar flow of newtonian fluids, the volume flow determination is based on the equation of Hagen-Poiseuille. The range of volume flow was 0.5 ml/h up to 50 ml/h.
Numerical Modelling of Droplet Deformation in a High-Pressure Homogeniser
Authors: Whyte David S. , Carnie Steven , Davidson Malcolm
Published: March 2009

A numerical study of droplet deformation in a high-pressure homogeniser is presented. This work is an attempt to identify flow criteria responsible for droplet break-up in a homogeniser used to produce dispersions for the manufacture of photographic paper. The main goal of this study is to recommend changes to homogeniser flow & geometry, operating conditions or fluid properties that will enhance droplet break-up. Laminar elongation, turbulent stresses within the orifice and downstream turbulence and cavitation have been suggested as possible mechanisms within the homogeniser for droplet rupture. Results for simulations, using a combination of homogeniser and droplet scale computation indicate that droplets are unaffected by local extensional flow or turbulent fluctuations and that other mechanisms must be responsible for droplet break-up.
Effects of Major Flow Path Shapes on the Flow Characteristics of APR1400 Fluidic Device
Authors: Cho Bong-Hyun , Bae Yoon-Yeong , Park Jong-Kyun
Published: March 2009

The effects of major flow path geometries on the flow characteristics of the Fluidic Device (FD) have been investigated experimentally and numerically. A full-scale FD has been designed and tested to verify a required characteristics, and the geometric effects are examined by changing internal shape of FD. As a characteristic of FD, time dependent flow rate, pressure and level change are discussed. Three dimensional numerical simulation by using commercial CFD code FLUENT-5 was also performed in order to predict the flow conditions, which can be used as input to the test and as the reference for the evaluation of test results. The flow patterns for high swirl cases were compared with a variation of inlet port shape, and an optimal shape are suggested in order to get a stable operations without entraining the gas in the tank through the supply port.