bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Sand Distribution on Erosion in Annular Three-Phase Flow
Authors: Mazumder Quamrul H. , Santos Gerardo , Shirazi Siamack A. , McLaury Brenton S.
Published: February 2009

Erosion in multiphase flow with entrained solid particles is a complex phenomenon due to existence of different flow patterns. Erosion experiments were conducted on an elbow specimen in a one-inch multiphase flow loop with gas, liquid and sand. Two different elbow specimens were used in the experiments. One placed downstream of a horizontal test section and one downstream of a vertical test section. Erosion tests were conducted at different gas and liquid velocities that showed a difference in erosion rates between the horizontal and vertical specimens. In order to better understand erosion results, the distribution of solid particles within the horizontal and vertical pipes just upstream of the elbows was measured across the pipe with a pitot probe. The results indicate that the distribution of sand in the pipe cross-section plays an important role in the erosion process due to the differences in velocities of the sand particles moving in the gas core and in the liquid film of the annular flow. It is observed that sand distribution in the horizontal test section is different than the sand distribution in the vertical test section for the same gas and liquid velocities. Therefore, the distribution of sand particles affects erosion test results. Based on these observations, a new mechanistic model has been developed to predict erosion in annular flow considering the effects of sand particle distribution and particle velocities in the annular film and gas core region. The experimental erosion results compare well with the model predictions.
Flow Patterns of Ice/Water Slurry in Horizontal Pipes
Authors: Hirochi Takero , Maeda Yasuhiro , Yamada Shuichi , Shirakashi Masataka , Hattori Ken Masaru , Saito Akihiro
Published: February 2009

The authors have observed flow patterns of ice/water slurry flow through horizontal circular pipes, and measured pressure loss for small diameter pipes, using three classes of ice particles. The slurry flows are classified into three patterns, i.e. dispersed-particle flow, cluster flow and column flow, and they are presented on a plane of two dimensionless parameters, i.e. the ice fraction f and the ratio of mixing energy to cohesion energy, πmix. The pressure loss for small diameter pipes is well estimated by the formula proposed previously by the present authors.
Wind-Induced Accidents/Troubles and the Lessons From Them
Authors: Matsumoto Masaru
Published: February 2009

This paper describes the wind-induced accidents and the lessons from them, taking some examples of trains, nuclear plant, bridges and electrical transmission systems. These are related to fluid/wind-induced force and vibration problems, and those are discussed from the fundamentals of bluff body aerodynamics.
A Mass Conservative Streamline Tracking Method for Three Dimensional CFD Velocity Fields
Authors: Li Zhenquan
Published: February 2009

Mass conservation is a key issue for accurate streamline visualization of flow fields. This paper presents a mass conservative streamline construction method for CFD velocity fields defined at discrete locations in three dimensions for incompressible flows. Linear mass conservative interpolation is used to approximate velocity fields. Demonstration examples are shown.
Flux Scheme: A Method for General Non-Conservative Two-Fluid Systems
Authors: Kumbaro Anela
Published: February 2009

This paper is concerned with numerical modeling issues arising when using a flux scheme for the approximation of two-phase flows. The paper puts emphasis on a general treatment of boundary conditions and reports on the interaction between an upwind discretization of the source terms and the boundary states. An upwind source term treatment consistent with the advection scheme results on an improved accuracy. Numerical results are provided to illustrate the method.
Local Liquid Velocity in Vertical Air-Water Bubbly Downward Flow
Authors: Sun Xiaodong , Paranjape Sidharth , Kim Seungjin , Goda Hiroshi , Ishii Mamoru , Kelly Joseph M.
Published: February 2009

Local characteristics of the liquid phase in downward air-water bubbly and slug flows were investigated in a 50.8-mm inner-diameter round pipe. A laser Doppler anemometry system was used to measure axial liquid velocity and its fluctuations. To reduce the measurement uncertainty, the experiments were performed in flow conditions with low void fraction. The comparisons between the liquid flow rates measured by the magnetic flow meter and those obtained from the local measurements showed good agreements. In addition, based on the LDA measurements and the data acquired by the local conductivity probes, the local relative velocity distribution, the distribution parameter and the drift velocity in the drift-flux model were obtained for the current downward flow.
A Characteristics-Based Approach to the Numerical Solution of the Two-Fluid Model
Authors: Nourgaliev Robert , Dinh Nam , Theofanous Theo
Published: February 2009

This paper is concerned with numerical solutions of the two-fluid models of two-phase flow. The two-fluid modeling approach is based on the effective-field description of inter-penetrating continua and uses constitutive laws to account for the inter-field interactions. The effective-field balance equations are derived by a homogenization procedure and known to be non-hyperbolic. Despite their importance and widespread application, predictions by such models have been hampered by numerical pitfalls manifested in the formidable challenge to obtain convergent numerical solutions under computational grid refinement. At the root of the problem is the absence of hyperbolicity in the field equations and the resulting ill-posedness. The aim of the present work is to develop a high-order-accurate numerical scheme that is not subject to such limitations. The main idea is to separate conservative and non-conservative parts, by implementing the latter as part of the source term. The conservative part, being effectively hyperbolic, is treated by a characteristics-based method. The scheme performance is examined on a compressible-incompressible two-fluid model. Convergence of numerical solutions to the analytical one is demonstrated on a benchmark (water faucet) problem.
Real Time and Quasi-3D Imaging of Gas-Liquid Flow Using Electrical Capacitance Tomography
Authors: Warsito W. , Fan L.-S.
Published: February 2009

In this study, an electrical capacitance tomography (ECT) adopted with neural-network based multi-criterion optimization image reconstruction technique (NN-MOIRT) for real time and quasi-3D imaging of gas-liquid flow system is developed. The technique reconstruct the permittivity distribution (tomography image) from capacitance data obtained using 12-electrode twin-plane capacitance sensor. A combined series and parallel capacitance model is used convert the permittivity distribution into gas holdup distribution. Comparison of the overall gas holdups obtained by the ECT with those obtained from the pressure measurements shows a good agreement, validating the model proposed. The ECT is applied to study the hydrodynamic characteristics of the gas-liquid flow system including the bubbly flow structures, gas holdup profiles, and gas holdup variations along with the effect of the gas velocity.
Streamwise Development of Co-Rotating, Paired Vortices Created by Tangential Injection
Authors: Holloway Mary V. , McClusky Heather L. , Beasley Donald E.
Published: February 2009

The present experimental study investigates the interaction and downstream development of two localized swirling flow structures created using a tangential injection method. A swirl generator is placed at the inlet of a 52.1 mm diameter pipe. The swirl generator consists of two swirl chambers with inner diameters of 23.8 mm. Each swirl chamber has a design swirl number of 7.14. Water is injected into each swirl chamber by two tangential injection ports. The injection ports are tangent to the swirl chamber and perpendicular to the axis of the pipe. The two co-rotating vortices created in the swirl generator interact freely within the pipe downstream of the swirl generator. The objective of the present study is to document the interaction between the two vortices and the downstream development of the flow. Lateral velocity fields are obtained using particle image velocimetry (PIV). Time-averaged lateral velocity fields and tangential velocity profiles are presented for several axial locations downstream of the swirl generator. Reynolds numbers of 11,000 and 17,000 are investigated. Results document the streamwise development and interaction between the two co-rotating vortices created by tangential injection. As the two swirling structures develop in the streamwise direction, three different types of flow patterns are identified. The first consists of two distinct swirling flow structures. Further downstream of the swirl chamber, the two swirling structures merge and form a single swirling flow structure with an elliptic core. In the third flow pattern, the center core of the swirling flow has a circular shape.
Computation of the Flow Around a Simplified Car Using the Rescaled v2–f Model
Authors: Manceau Re´mi
Published: February 2009

The Ahmed body is a simplified car used in automotive industry to investigate the influence of the flow structure on the drag. When the angle of the hatchback approaches 30°, the wake of the body experiences a transition from a quasi-2-D to a fully 3-D structure, which is at the origin of a drag crisis. Many turbulence models have been tested for the case at 25° and none of them was able to reproduce correctly the complex flow structure. The paper aims at investigating the performances of a recently developed near-wall eddy-viscosity model, the rescaled v2–f model, which is derived from the well known v2–f model. It is shown that the model does not perform better than models of the same class. Indeed, the predicted wake is nearly 2-D, massively separated, which is characteristic of the low-drag configuration: the transition of the wake to a fully 3-D, highly dissipative structure is not reproduced.
Fluid Dynamics in Critical Nozzles Revealed by Measurements (Keynote)
Authors: Ishibashi Masahiro
Published: February 2009

The paper describes primary calibration of high-precision nozzles (HPNs), which have ideal geometries, at critical condition, theoretical calculation of the discharge coefficient to be verified by the primary calibration, concept of fluid dynamical standard using HPN, precise measurement of boundary layer transition in HPNs in terms of flowrate, superfine structure in the critical flowrate, discrepancy which can occur between primary calibrations and field applications of critical nozzles, and 3D flow velocity field measurements based on recovery temperature, which visualizes many interesting phenomena in axi-symmetric transonic flow as shock interactions, acceleration by edge, reflection of shocks, Fano flow and so on.
Optical Shock Wave Imaging for Aviation Security
Authors: Settles Gary S. , Benwood Jeremy R. , Gatto Joseph A.
Published: February 2009

This paper is about shock wave propagation inside an aircraft fuselage, caused either by a terrorist device or by an accidental explosion. The concern over blasts inside airframes, stemming from past terrorist attacks on commercial aviation using concealed explosives, continues unabated and extends to luggage, passengers, and air cargo. In earlier publications by the present authors, it was noted that all previous aviation security studies lacked optical shock imaging, the principal tool of explosion and shock wave research. In an effort to correct this, high-speed schlieren shock wave cinematography methods on a large scale are demonstrated here for aircraft hardening studies. This capability is used to examine shock propagation in realistic aircraft interior scenarios, as well as to carry out some basic experiments toward an improved understanding of internal blast wave behavior.
Instantaneous Liquid Flow Rate Measurement Utilizing the Dynamic Characteristics of Laminar Flow in Circular Pipes
Authors: Manhartsgruber Bernhard
Published: February 2009

The instantaneous measurement of transient flow rates is an important problem in many fluid power applications such as the investigation of the flow ripple generated by hydraulic pumps or the measurement of flow rate changes at the ports of fast switching valves. This paper deals with the utilization of the dynamic characteristics of laminar flow in circular pipes for the indirect measurement of flow rates. A discrete time state space realization of the transmission line dynamics is computed via inverse Laplace transform and an identification and model reduction method based on the singular value decomposition. This dynamic system is used for the computation of the flow rate at one end of a pipe section. Special attention is paid to the identification of the speed of sound and the dimensionless dissipation number of the pipe section, since exact knowledge of these parameters is crucial for the reliabilty of the measurement results.
Forced Convection From a Stationary Cylinder Placed in a Uniform Stream
Authors: Baranyi La´szlo´
Published: February 2009

A finite difference solution is presented for 2D laminar unsteady flow around and forced convection from a stationary cylinder placed in an otherwise uniform flow. The fluid is assumed to be incompressible and of constant property. The temperature of the cylinder wall is kept constant, and the viscous energy dissipation term is neglected in the energy equation. The computed Strouhal numbers, time-mean drag and base pressure coefficients, as well as the average Nusselt numbers compare well with existing experimental results. The distribution of the local Nusselt number on the cylinder was investigated over a complete vortex shedding cycle, and shifts in Nu belonging to different phases were identified.
Numerical Simulation of Flow-Induced Vibration of a Rectangular Cylinder
Authors: Enya Atsushi , Okajima Atsushi
Published: February 2009

It is important for industrial purposes to predict flow-induced vibration of a bluff body elastically supported in an uniform flow. In this paper, the free oscillation of a rectangular cylinder with two-degree of freedom in the streamwise (in-line) and cross-flow (transverse) directions in a uniform flow, was computed by the Large Eddy Simulation (LES) method at high Reynolds number of 2.2 × 104. The Smagorinsky model was used as a subgrid scale (SGS) model. The main objectives of this work were to predict and estimate characteristics of flows around a free-oscillating cylinder. The present computations successfully reproduce various types of flow-induced vibrations of a free-oscillating rectangular cylinder as found by experiments; in-line oscillation, eddy-excitation and low-velocity galloping.
Detailed 3D Rotor-Stator Interaction in Automotive Engine Cooling Fan Systems
Authors: Henner M. , Moreau S.
Published: February 2009

In order to address the interaction of the automotive engine cooling fan with its system environment, the unsteady interaction of the fan blades with its support struts or stator vanes is presently studied. The resulting unsteady sources are consequently used to predict the tonal noise of such systems. Preliminary detailed 2D unsteady simulations at a given mean radius have helped testing the necessary numerical spatial and time parameters. A newly developed acoustic post-processing code RSF based on the Acoustical Analogy for both Rotor and Stator blades in the Frequency domain, has then been used to compute the fan system tones. An initial coarse 3D simulation has stressed the crucial role of the spatial resolution and had motivated the consequent refined simulation of the complete reference fan system, for which the main features and preliminary results are highlighted here. A first comparison with experimental noise data on a similar system also suggests a partial contribution of this mechanism to the spectral tones.
Microbubble Transport in Turbulent Channel Flow
Authors: Vance Marion W. , Sugiyama Kazuyasu , Takagi Shu , Squires Kyle D.
Published: February 2009

Microbubble transport in fully developed turbulent channel flow is investigated using an Eulerian-Lagrangian approach. The carrier-phase flow is computed using Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES) of the incompressible Navier-Stokes equations. Lagrangian particle tracking is employed for a dispersed phase comprised of small, rigid spheres of negligible density compared to the carrier-phase flow and obeying an equation of motion in which the forces used to predict the motion of the bubble are drag, pressure gradient, and added mass. In general, DNS and LES yield similar predictions of the carrier phase flow and dispersed-phase properties. The bubble Stokes number is varied over a range for which the dispersed phase essentially follows the carrier flow to larger values for which strong segregation of the microbubbles into coherent vortical structures occurs. In general, simulation results show that microbubble response is not a monotonic function of the Stokes number. The most significant structure in the concentration field occurs for Stokes numbers close to the turbulence timescales in the buffer layer. More than 2/3 of the microbubble population in the buffer layer resides in coherent structures that occupy approximately 1/3 of the computational volume.
Relation of Polymer Drag Reduction to Structure and Molecular Weight (Keynote)
Authors: Vlachogiannis Michael , Liberatore Matthew , McHugh Anthony J. , Hanratty Thomas J.
Published: February 2009

The influence of molecular weight distribution on polymer drag reduction was studied for solutions of partially hydrolyzed polyacrylamide by analyzing the solution over a period of time during which the polymer was degrading. No relation was observed between the effectiveness of this polymer solution and molecular weight.
Studies of Vibration-Induced Multi-Phase Fluid Phenomena and Pulsating Heat Pipe Performance Under Microgravity
Authors: Kawaji Masahiro
Published: February 2009

High quality semi-conductor and protein crystals can be grown in space by utilizing the microgravity environment in which natural convection and sedimentation effects are suppressed. But some vibrations exist on space platforms such as Space Shuttle and International Space Station that can induce crystal and fluid motions, affecting the quality of the crystals grown in space. Since the effects of small vibrations (called g-jitter) on crystal growth are not yet precisely known in space, experimental and theoretical investigations are being conducted to better understand the vibration effects on the motion of protein crystals and solid particles in liquid-filled cells. Another topic under investigation is the operation of pulsating heat pipes under microgravity. A recent experiment performed on a parabolic airplane has shown the positive effect of reduced gravity on the pulsating motion of vapour-liquid two-phase flow and heat transport in pulsating heat pipes.
Numerical Study on the Effect of Agglomeration for the Particle Separation in a Gas Cyclone
Authors: Ho C. A. , Sommerfeld M.
Published: February 2009

Numerical calculations of multiphase flow processes become of increasing importance for process analysis and optimization. For predicting the particle separation in a gas cyclone, the well known Euler/Lagrange approach is most suitable. With this method it is possible to account for the particle size distribution and transport processes such as particle-wall and inter-particle collisions.
Microbubble Drag Reduction: A Simple and Complex Phenomenon
Authors: Kato Hiroharu
Published: February 2009

Reduction of drag represents a major target for researchers and engineers who are engaging in fluid dynamics. Recent developments of fluid dynamic knowledge have generated reductions in the form drag of vehicles and wave making drag of ships. The reduction of frictional drag is the last and most difficult target. For example, a major part of a ship’s drag is the frictional drag (more than 80% for low speed ships such as tankers). Several methods have been proposed and tested; riblets, LEBU, polymers, microbubbles etc. Among them, microbubbles seem the most promising, because of large reductions that may be possible (more than 50%). The injection of microbubbles is also simple and environmentally friendly. Bubbly flow is a fundamental multi-phase flow and has been studied for a long time. Practical applications are widespread; from the flow inside a boiler tube to the agitation of mixing and chemical reaction. The frictional drag reduction by microbubbles was discovered 30 years ago by McCormick and Bhattacharyya [1]. Since then, many scientists have studied this phenomenon. Recent research in Japan includes a full-scale experiment on a 116m long ship [2]. The author was involved in those research projects, and has pondered the mechanism with young colleagues. One might think that the mechanism of drag modification is well understood since bubble flow is very common and very simple. However, the effect of microbubbles on turbulence is complex and poorly understood. Little is known of how microbubbles reduce the frictional drag in the turbulent flow. Recent measurements at the National Maritime Research Institute (NMRI), Tokyo and the Toyo University, Kawagoe showed that the turbulent intensity increases with the addition of microbubbles but the Reynolds stress decreases [2][3]. Existing hypothesis cannot explain these observations. We also have noticed both in the laboratory experiment and in the full-scale test that the microbubbles need to be very near to the wall in order to achieve drag reduction. But, how near should they be? The answer has important consequences in practical applications, because if we can concentrate the microbubbles in the most effective region, the energy needed for ejecting microbubbles can be much reduced. Much remains to be learnt regarding drag reduction by microbubbles.
Brownian Dynamics Simulation in a Turbulent Channel Flow
Authors: Terrapon Vincent E. , Dubief Yves , Moin Parviz , Shaqfeh Eric S. G.
Published: February 2009

The dynamics of different bead-spring models is investigated in a turbulent channel flow. In particular, the FENE, the FENE-P and the FENE multichain models are compared. In the case of the FENE-P model, both the Brownian Dynamics and the constitutive equations are used. It is shown that the different models produce qualitatively similar results for the mean extension and the mean stresses. This qualitative behaviour is also reproduced for different extensibility parameters. It is also found that the action of polymers is confined in the near wall region where the polymers are mainly oriented in the streamwise direction.
Advanced Unsteady Flow Control (Keynote Paper)
Authors: Bayandor Javid
Published: February 2009

A general description, underlining some of the defining principles behind the revolutionary advanced unsteady propulsive system, is provided. The developed system is a large amplitude unsteady propulsion that leaves free trailing vorticity of magnitude O (ε0) per unit of time down-stream of the flow. Having multiple degrees of freedom (sixteen for the scaled-down prototype) the system has been designed to efficiently operate in transitional and unsteady flows through sensing and capturing the energy of flow perturbations and turbulence in addition to that of the free-stream. Numerical studies, backed by experimental data, have demonstrated the high efficiency gain of the system in comparison to the conventional turbomachinery.
Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)
Authors: Watmuff Jonathan H.
Published: February 2009

Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.
Observation and Numerical Simulation for Wet Chemical Etching Process of Semiconductor
Authors: Kaneko Kimihisa , Noda Tomoyoshi , Sakata Masayoshi , Uchiyama Tomomi
Published: February 2009

This paper concerns with the basic investigations on the wet chemical etching of semiconductors. First, a method to observe the etched cross-section of aluminum layer is developed. It is applied to the observation for the cross-section of a test piece etched in a quiescent etchant. The observation successfully makes clear the time variation for the geometry of the etched cross-section, and elucidates the effects of the resist width on the geometry. Secondly, the numerical simulation for the etching process is performed. The simulated geometry of the etched cross-section is confirmed to agree with the observed result, indicating that the present numerical simulation is effectively used to predict the geometry of the etched cross-section.
The Equation of Motion and Energy Equation for Particles: A Historical Perspective (Keynote)
Authors: Michaelides Efstathios E.
Published: February 2009

Energy and momentum exchange between spherical particles and a fluid is a fundamental problem that has excited the intellectual curiosity of many scientists for more than two centuries. The development of the energy equation of spherical particles in a fluid can be traced back to the work of Laplace and Fourier that appeared early in the 19th century. It is now little known that Peclet formulated the no-slip condition at a solid boundary, by observing the transfer of heat, approximately ten years before the concept of viscosity was conceived. Towards the middle of the 19th century Poison derived the hydrodynamic force on a sphere in an inviscid fluid and a few years later, Stokes formulated what is now known “the Stokes drag” for the steady-state hydrodynamic force acting on a spherical particle in a viscous fluid. Boussinesq and Basset developed a form for the transient equation of motion of the particles with very low inertia towards the end of the 19th century. The mathematical advances of the early 20th century are reflected in developments in mechanics and on the equation of motion of particles. Oseen and Faxen used asymptotic methods to derive improved our knowledge on the behavior of particles with inertia and in close proximity to boundaries. Experimentation contributed very useful correlations on the hydrodynamic force and the heat transfer from particles. The experimentally derived data helped also in the development of semiempirical equations for the transient hydrodynamic force. Regular and singular perturbation methods have been used more recently to derive expressions for the transient hydrodynamic force and the heat transfer from particles during time-dependent processes, both under creeping flow conditions and at low Reynolds or Peclet numbers. The recent advances on computational methods and the exponential increase in computer power enable us to simulate the motion and energy exchange of groups of particles and complex particle interactions. This presentation gives a historical perspective on the development of our knowledge on particle motion and heat transfer inside a viscous or conducting fluid. Emphasis is given on the exposition of the lesser-known works of the 19th century that have placed the foundation for many concepts and methods that are still used today. The presentation concludes with the most recent contributions of the numerical studies and a short exposition of the voids in our knowledge on energy and momentum exchange processes between particles and a fluid.
Measurement and Computation of Turbulence in Risers Using Kinetic Theory
Authors: Tartan Mehmet , Gidaspow Dimitri , Jung Jonghwun
Published: February 2009

Detailed experimental velocity, particle concentration and stresses for flow of particles in a vertical pipe, riser are needed for verification of various CFD models for multiphase flow in the industrially important circulating fluidized bed (fast fluidization) regime. This study provides such information for flow of 530 μm glass beads in the fully developed flow region of a 7 m symmetric riser with a splash plate. Instantaneous particle velocity distributions were obtained using a particle velocity imaging technique and a probe inserted into the riser, while the particle concentrations were measured with a gammaray densitometer. Time averaged particle velocity distributions can be well represented by a parabolic velocity distribution, with the mean velocity obtained from flux divided by the measured bulk density. The radial granular temperature profiles agree with an analytical expression similar to the thermal temperature distribution in Poiseuille flow with viscous heat generation. A solution to the complete CFD model shows that the assumptions made in the analytical solution are valid. Our measurements of stresses in the risers and bubbling beds show the existence of two types of random kinetic energies or granular temperatures. The true granular temperature is due to oscillations of particles, while the second is the average of the normal Reynolds stresses. In the core of the riser, the true granular temperature is much larger than the Reynolds type granular temperature. The reverse is true in the bubbling bed.
Why Are Relationships Between Lagrangian and Eulerian Scales Necessary for Gas-Particle Flow Modeling?
Authors: Huilier Daniel
Published: February 2009

Simulation of Gas-Particle flows can be fulfilled by Lagrangian modeling of the dispersed phase. Each type of Lagrangian method, Monte-Carlo/Eddy Interaction or Markov Chain models, needs the knowledge of Lagrangian scales associated with the turbulent flow under consideration and the type of particle dispersing in the gas carrier flow. Unfortunately, Lagrangian quantities (as well the interesting moving Eulerian time scale, that given by a sensor which would move with the mean fluid velocity) are still difficult to be obtained directly by most experimental measurement techniques (except by very recent techniques such as PIV.PTV.), contrary to Eulerian scales scales, such as those classically obtained from a fixed hot-wire or LDA control volume. It is therefore of great importance to have available accurate relationships between Eulerian and Lagrangian scales, based on fluid flow properties as well as particle characteristics.
Inter-Particle Collisions: Analytical Approach for Closure of Driving Equations of Dispersed Phase in Gas-Solid Particle Flows
Authors: Kartushinsky Alexander , Michaelides Efstathios E.
Published: February 2009

Two mechanisms for the particle-particle collisions—with and without frictional sliding collision are considered in this paper to take into account the effect of the particle-particle collision on the motion of solid particles in two-phase turbulent pipe and channel flows. Based on these mechanisms the correlations of the various velocity components of colliding particles are obtained analytically by using an averaging procedure, which takes into account three collision coordinates, two angles and one geometrical distance between the centers of colliding particles. As a result the various stress tensor components are obtained and then introduced in the mass, linear momentum and angular momentum equations of the dispersed phase. They are considered as additional force factors together with the influence of the particle-turbulence interactions, the viscous drag force, the two types of lift force (Magnus and Saffman) and the gravitational force. The approach applies to the particle-particle collisions based both on the average velocity difference between colliding particles and to the turbulent velocity fluctuation of colliding particles. To close the governing equations of the dispersed phase, the pseudoviscosity (and pseudodiffusity) coefficients with collision origin are determined as well, using a Bousinesque-type eddy-viscosity approach. [To close the governing equations of the dispersed phase, the stress tensor components as well as the pseudoviscosity (and pseudodiffusity) coefficients defined with the help of using a Bousinesque-type eddy-viscosity approach are determined here.] In order to obtain these coefficients the time of the inter-particle collision is calculated from the information on the collision process. The model covers the motion and collisions of both polydisperse and monodisperse particulate systems. The model is validated by comparison with the experimental data of Tsuji et al. (1984) for a vertical pipe.
Closure Approximations for PDF Equations Based on the Simonin-Deutsch-Minier (SDM) Equation for Gas-Particle Flows
Authors: Reeks Michael W.
Published: February 2009

The paper addresses an apparent incompatibility between the two current formulations of the PDF approach for the dispersion of particles in a uniform shear flow. It is shown that this incompatibility arises through neglect of the inertial convection term in the transport equation for the mean carrier flow velocity local to a particle. Evaluating this term for a Gaussian process gives identical results for both formulations. This also resolves a long standing incompatibility in previous forms for the fluid point diffusions coefficients in a simple shear. A closure approximation is given based on a Gaussian model for the contribution due to the fluctuating shear which has previously been assumed to be white noise in the generalised Langevin model (GLM) due to Simonin, Deutsch and Minier.
Numerical and Experimental Study of Particle Rebounding Flow Characteristics in a Gas-Particle Flow Over Curved Bodies
Authors: Tu J. Y. , Yeoh G. H. , Morsi Y. S. , Yang W.
Published: February 2009

The particle rebounding characteristics of a gas–particle flow over a cylindrical body and an in-line tube bundle arrangement is investigated. With the aim of adopting both numerical and experimental approaches, the mean particulate flow patterns, comprising both incident and rebound particles resulting from the impact of particles on solid walls, are examined. Experimentally, a two-dimensional Laser-Doppler Anemometry (LDA) technique is used to measure the instantaneous incident and rebound particle velocities in the immediate vicinity of body surfaces. Computationally, the Reynolds-Averaging Navier-Stokes equations are solved for the continuum gas phase; the results are used in conjunction with a Lagrangian trajectory model to predict the particle-rebound characteristics. For a single tube model, the computational observations, also confirmed through experiment, reveal a particle rebound zone where the mean particulate flow pattern is significantly modified due to the contribution of the rebound particles during particle-wall impact interaction. For the in-line tube bundle model, particles being rebounded from the first row of tubes at upstream migrated downstream and impinged the other tubes in an extremely complex and random disposition. Analysis of the effect of the above-mentioned parameters on the rebounding particle flow characteristics has provided a better understanding on the behaviour of particulate flow impinging on curved solid wall bodies.
Numerical Simulation of Particulate Jet Generated by Free Falling Particles
Authors: Uchiyama Tomomi
Published: February 2009

This paper is concerned with the numerical simulation of the particulate jet generated by solid particles falling from a slit orifice into an unbounded quiescent air. A two-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in prior papers, is employed for the simulation. The falling particles induce complicated airflow involving eddies with a wide variety of scales. The air takes its maximum velocity at the jet centerline. The particle velocity is higher than the free falling velocity of a single particle. The effects of the diameter and density of the particle on the flow are investigated. The entrained airflow rate is favorably compared with the value predicted by an analytical model.
Numerical Simulation of Coal Ash Particle Behavior in Entrained Flow Coal Gasifier
Authors: Watanabe Hiroaki , Ichikawa Kazuyoshi , Otaka Maromu , Inumaru Jun
Published: February 2009

The objective of this study is to develop an evaluation tool for a design and performance of a coal gasifier by a numerical simulation technique. In the present paper, a gas-particle two phase reacting flow calculation is carried out for a prediction of phenomena in an entrained flow coal gasifier due to coal and ash particles behavior, such as ash deposition on the wall. A transportation of the coal particles is modeled via a Lagrangian manner. The ash particle adhesion on the wall of the gasifier is discriminated by an empirical ash adhesion model based on a liquid phase fraction concept in the ash particle. The gas phase properties are calculated by three dimensional time-mean Eulerian conservation equations. The turbulent flow field is determined by the k-ε two equations model. Radiative heat transfer is calculated by the discrete transfer radiation method. Coal gasification reaction model is composed of three chemical processes in the current model: a pyrolysis, a char gasification and gas phase reactions. 2 tons/day (t/d) air-blown pressurized entrained flow coal gasifier, which has been constructed and operated by Central Research Institute of Electric Power Industry (CRIEPI) was targetted. As a result, a relationship between an operating condition (air ratio) of the gasifier and the gasifier performance is presented. The trend of the ash deposition on the gasifier inner wall is also presented. Comparison between the computational and the experimental results shows that the most feature of the gasifier performance and the profile of the ash deposition have been captured by the present model. It was confirmed that the numerical simulation approach is very useful for the assessment of gasifier performance and operation support.
Visualization of Pressure Field in Turbulent Wake Between Two Bluff Bodies
Authors: Tokai Norihiko
Published: February 2009

An experimental method to visualize the instantaneous pressure field in turbulent flow has been proposed. Numerical solution of the discrete Poisson equation for pressure was sought, where the instantaneous velocity data was supplied by PIV measurement. The validity of the method was assessed by referring to available DNS data for wake of a rectangular cylinder. The method was applied to evaluate the instantaneous pressure distribution in the region between two columns set in tandem in uniform flow. It is shown that the correlation between fluctuating velocity and pressure gradient plays an important role in determining the turbulence structure in the wake, which is indicated by the fact that the normal component of Reynolds stress in front of the column set in the wake of another is extremely large where the velocity-pressure correlation overtakes the production rate.
A Way Towards Optimization of Injection Molding
Authors: Courbebaisse G. , Garcia D. , Bourgin P.
Published: February 2009

Injection molding of thermoplastic is a complex process essentially because of the physical properties of the polymers, the processing conditions and the mold geometry. One key issue is to find the optimal location of the injection point(s) so that to minimize the final pressure required to fill the mould. This is usually achieved by using commercial computer codes, which are time consuming. Our approach, which is not classical, consists in introducing several “geometrical tools” of image analysis such as optimal centering and skeleton transformation, to characterize the shape properties of the flow filling the mould cavity. A direct correlation between the geometrical parameters associated to image analysis and the results based on the classical Hele-Shaw model is obtained for several molds. Furthermore, the physical problem is not completely taken into account by the mathematical formulation based on the considered geometrical tools. It is the reason why a new formulation is proposed, taking the governing equations of the model into consideration. As the physical problem is of an elliptic form, its energetic formulation can be used to answer our problematic. In son doing, for a given fluid, the optimal position of the injection points can be found by writing a quadratic optimization problem. In this paper, we present the first results devoted to the optimization of the filling phase.
Bend Loss Coefficient of Drag-Reducing Surfactant Solution
Authors: Imao Shigeki
Published: February 2009

In this study, an effect of an additive on a bend loss was examined. Measurements of pressure distributions along pipes connected to pipe bends were performed using a drag-reducing surfactant solution. The additive used is being commercialized as a drag reducer and it has a non-degrading or rapidly repairable nature. Dimensions of the apparatus are pipe diameters d = 5, 10, 15 mm, radius ratios R/r = 20, 40, 60, 100, and a bend angle θ = 180 degree. It has been confirmed that total bend loss coefficients for water can be expressed by the equation deduced by Ito. When the surfactant solution is used, remarkable drag reduction was recognized in the inlet and the exit straight pipes. Pressure recovery length for the surfactant solution after the passage of the bend is longer than that for water. The curve of total bend loss coefficients for the surfactant solution intersects that for water. The former is larger than the latter at low Reynolds number and is smaller at high Reynolds number. The coefficients don’t depend on the pipe diameter but they depend on the radius ratio. It is shown that total bend loss coefficients for the surfactant solution can be expressed by a single curve and the empirical formula is deduced.
Vortex Motion in a Swirling Flow of Surfactant Solution With Drag Reduction in a Pipe
Authors: Munekata Mizue , Matsuzaki Kazuyoshi , Ohba Hideki
Published: February 2009

A surfactant is well known as an additive that brings about drag-reduction in straight (non-swirling) pipe flow. However in industrial applications of the drag-reducing effect, many flow fields exist including the straight pipe flow. The purpose of this study is to investigate the flow characteristics of surfactant solution swirling pipe flow. The drag reducing effect is estimated from the measurement wall pressure loss and the velocity profiles on various pipe sections are measured by 2 dimensional LDV. Since the surfactant solution has viscoelasticity, interesting flow characteristics are shown. The decay of swirl, the vortex type and the turbulence intensity are discussed, compared with the water swirling flow. The oscillating of vortex core is also investigated.
Particle Structure Evolution in Micro Flow of Electrorheological Suspensions in Nonuniform Electric Fields
Authors: Kadaksham J. , Batton J. , Singh P. , Aubry N.
Published: February 2009

A modified version of the distributed Lagrange multiplier method (DLM) [11] is used to study the dynamics of particle scale structure in electrorheological (ER) liquids subjected to spatially non-uniform electric field (also see [7, 18]). The time duration in which the particles are collected, near the electric field magnitude minimums or maximums, depends on a parameter defined by the ratio of the dielectrophoretic and viscous forces. Another parameter defined by the ratio of the electrostatic particle-particle interaction and dielectrophoretic forces also influences the time duration in which the particles are collected, as when this parameter is greater than one the particles to organize in chains which decreases their speed. The numerical results agree qualitatively with experiments which show that when the electrostatic particle-particle forces dominate the particles form chains that collect near the electrode edges.
Numerical Turbulent Analysis for Flow Around a Square Cylinder Using the Finite Element Method
Authors: Miura Shinichiro , Kakuda Kazuhiko
Published: February 2009

A finite element scheme based on the Petrov-Galerkin weak formulation using exponential weighting functions for solving accurately, and in a stable manner, the flow field of an incompressible viscous fluid has been proposed in our previous works. In this paper, we present the Petrov-Galerkin finite element scheme for turbulent flow field. The incompressible Navier-Stokes equations are numerically integrated in time by using a fractional step strategy with second-order accurate Adams-Bashforth explicit differencing for both convection and diffusion terms. Numerical results obtained herein are compared through turbulent flow around a square cylinder at Re = 22,000 with the experimental data and other existing numerical ones.
Migration and Settling of Particulates in Filled Epoxies
Authors: Mondy Lisa , Rao Rekha , Lindgren Eric , Sun Amy , Lagasse Robert , Thompson Kyle
Published: February 2009

Manufacturing applications for filled polymers include encapsulation of microelectronics and injection molding of composite parts. Predictive tools for simulating these manufacturing processes require knowledge of time- and temperature-dependent rheology of the polymer as well as information about local particle concentration. The overall system rheology is highly dependent on the particle concentration. The local particle concentration can change due to gravity, convection and shear-induced migration. For the epoxy systems of interest, an extent of reaction can be used to track the degree of cure. We couple the curing model with a diffusive flux suspension model [Zhang and Acrivos 1994] to determine the particle migration. This results in a generalized Newtonian model that has viscosity as a function of temperature, cure and concentration. Using this model, we examine settling of the particulate phase in both flowing and quiescent curing systems. We focus on settling in molds and flow in wide-gap counter-rotating cylinders. The heat transfer, including the exothermic polymerization reaction, must be modeled to achieve accurate results. The model is validated with temperature measurements and post-test microscopy data. Particle concentration is determined with x-ray microfocus visualization or confocal microscopy. Agreement between the simulations and experimental results is fair.