bluuebunny/crossref_metadata_2025 huggingface dataset:
A Methodology for Simulating Compressible Turbulent Flows
Authors: Fasel Hermann F. , von Terzi Dominic A. , Sandberg Richard D.
Published: February 2009

A Flow Simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modelling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for RANS) and scaling of the model terms with a “contribution function”. The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This “physical” resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modelling if the computation is locally well resolved so that it approaches a DNS in the fine-grid limit and such that it provides modelling of all scales in the coarsegrid limit and thus approaches an unsteady RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modelling for the unresolved scales while the larger (resolved) scales are computed as in traditional LES. However, FSM is distinctly different from LES in that it allows for a consistent transition between (unsteady) RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a traditional LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step at low Mach number and a supersonic, axisymmetric baseflow. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for a wide range of compressible flows.
Simulating Turbulent Flows in Complex Geometries
Authors: Mahesh Krishnan , Constantinescu George , Moin Parviz
Published: February 2009

We discuss development of a numerical algorithm, and solver capable of performing large-eddy simulation (LES) in geometries as complex as the combustor of a gas-turbine engine. The algorithm is developed for unstructured grids, is non-dissipative, yet robust at high Reynolds numbers on highly skewed grids. Results from validation in simple geometries is shown along with simulation results in the exceedingly complex geometry of a Pratt & Whitney gas turbine combustor.
Feasibility Studies on a Small-Scale Wind Turbine for the Mountainous Area
Authors: Kamada Yasunari , Yamanaka Kazuma , Maeda Takao , Shimizu Yukimaru
Published: February 2009

In this study, a small-scale wind turbine for the mountainous area is developed. The technical features of this wind turbine are the high performance rotor with a blade tip-mounted Mie vane, the passive power control by a pitch-flap mechanism and a variable speed induction generator with inverter system. The test wind turbine is tested in Mie University wind turbine test field in a mountainous area. The output power performance, the passive power control in high wind speed, the performance improvement by the variable speed operation and the quality of power are discussed. As the results, it is demonstrated the power control by a passive pitch-flap mechanism, the suppressing effects for the fluctuating moments on the blade root and the characteristics of the variable speed generating system. Some flow patterns on the blade are shown.
Flow Distribution and Slug Flow Characteristics for Hydraulically Equilibrium Air-Water Two-Phase Flows in a Vertical 2×3 Rod Channel
Authors: Kano Keiko , Sadatomi Michio , Kawahara Akimaro , Kuno Tsukasa
Published: February 2009

To complete subchannel analysis for predicting thermal-hydraulic behavior of coolant in a BWR rod bundle channel, accurate estimation of fluid transfer between subchannels is necessary. In order to validate a prediction method, flow distributions data of gas and liquid phases are essential. But, such data reported so far are limited to those in a two-subchannel system alone. Then we have measured flow distributions of both phases and Taylor bubble velocity in a multi-subchannel system as called 2×3 rod bundle channel. It has been found that flow distributions of gas and liquid in bubble and annular flows under a hydraulically equilibrium flow condition are close to those of single-phase flow, but in slug-churn flow the distributions are different. In slug-churn flow, both superficial gas velocity and Taylor bubble velocity are higher in larger subchannel. These experimental data are presented and discussed in this paper.
Flow Structure and Pressure Loss of Two-Phase Flow in Helically Coiled Tubes
Authors: Ishikawa Masa-aki , Oiwa Hiroshi , Sakai Kosuke , Murai Yuichi , Toda Shin-ichi , Tamayama Kiyoshi , Yamamoto Fujio
Published: February 2009

In the steam generator of the prototype FBR (Fast Breeder Reactor) in Japan, heat exchange tubes of helical coil type are utilized. The gas-liquid two-phase flows in the helical coil tube have different characteristic from straight tubes due to the effects of centrifugal acceleration in the curved tubes. In our study, the interfacial structure of the gas-liquid two-phase flows in the helical coil tube is visualized to provide the flow pattern map. Simultaneously, the pressure loss and its local fluctuation are measured in order to investigate the dynamic characteristics of the two-phase flow appearing in the helical coil tube. The result reveals that the bubbly flow regime extends and the stratified flow vanishes compared the gas-liquid flow in a horizontal straight tube. Moreover, the slug flow has asymmetric structure due to the effect of centrifugal acceleration. On the contrary the pressure loss is basically not remarkably different from the straight tube except the fact that the pressure has a high fluctuation component.
Multi-Channel R134a Two-Phase Flow Measurement Technique for Automobile Air-Conditioning System
Authors: Gu Junjie , Kawaji Masahiro , Smith-Pollard Tracey , Cotton James
Published: February 2009

This paper presents an improved on-line measurement technique developed to study two-phase flow rate distributions of refrigerants in parallel flow channels of compact heat exchangers and evaporators used in automotive air-conditioning systems. A prototype test station containing a refrigerant flow loop and a multi-channel two-phase flow measuring system, was designed and constructed based on the stratification of two-phase flow in horizontal tubes with relatively large diameters. In this work, glass tubes of 1”, 1.5” and 2” diameter were tested. Upon entering the glass tube, a vapour-liquid refrigerant mixture would readily stratify and the mean velocities of vapour and liquid phases could be measured separately using a hot film anemometer and an ultrasonic flow meter, respectively. Scales taped onto the glass tubes were also used to determine the mean liquid levels, from which the flow area of each phase could be calculated. The product of the flow area, phase density and mean phase velocity would then yield the mass flow rate of each phase. Validation experiments have been performed with R-134a as the working fluid and a 3-channel evaporator test section, designed with three separate outlets and kept under an adiabatic condition. The sum of the flow rates in the glass tubes for each phase was compared with the vapour or liquid flow rate determined from the total mass flow rate measured at the evaporator inlet and a heat balance in the pre-heater section of the pump-driven refrigerant flow loop. Validation tests yielded satisfactory results for both vapor and liquid phases, indicating the soundness of the measurement system based on the stratification tubes as well as the use of an ultrasonic flow meter and hot-film anemometer probes for phase average velocity measurements. The present measurement system has been equipped with seven glass tubes and thus can be used to study liquid and vapor flow rate distributions in commercial compact heat exchangers and improve their performance in automobile air conditioning systems.
Large Eddy Simulation of Spray Combustion in Swirling Flows
Authors: Itoh Yuichi , Taniguchi Nobuyuki , Kobayashi Toshio , Tominaga Takuji
Published: February 2009

Large Eddy Simulation (LES) of turbulent spray combustion flow was conducted. An experimental model of the spray combustor which has benchmark experimental database is chosen to validate the present numerical simulation. The governing equations for the gas phases are discretized in curvilinear boundary-fitted coordinate system, and the fuel droplet motion equations are described in Lagrangian representation. The numerical results such as gas-phase mean velocities agree with the experimental results. Three dimensional vortical structures and droplet motion by swirling air are well visualized, and droplet velocities agree with experimental results.
A Numerical Investigation of the Interaction Between Rotor Bow Waves and Upstream Wake Generators in a Transonic Compressor Stage
Authors: Bloch Gregory , Loellbach James , Hah Chunill
Published: February 2009

A numerical investigation of unsteady blade row interaction in a transonic axial compressor was performed. The compressor consists of an upstream wake generator (WG) blade row followed by a rotor blade row. Blade row interaction consists of two main effects: the downstream influence on the rotor flowfield of wakes and unsteady vortices shed from the wake generator, and the upstream influence on the wake generator of the rotor bow shock waves. An unsteady, two-dimensional, Navier-Stokes simulation was performed at the 75% span location of the compressor. Results from the numerical simulation are compared to previously reported numerical results and to experimental measurements from a similar case.
Numerical Simulation of Hysteresis on Head/Discharge Characteristics of a Centrifugal Pump
Authors: Iino Masamichi , Tanaka Kazuhiro , Miyagawa Kazuyoshi , Okubo Takeshi
Published: February 2009

The objectives of the present study were to investigate influences of fins, set in a suction part, on the positive slope and hysteresis loop in head/discharge characteristic curves of centrifugal pumps in the experiment as well as in the numerical prediction. The fins were located in upstream side of a pump impeller to suppress swirl flow occurring before the impeller inlet at partial load operation. We had two kinds of centrifugal pump with/without the fins, the number of which is 16. These two centrifugal pumps had a shrouded impeller with 7 blades and a diffuser with 20 guide vanes with the same configuration. In the experiment, the pump with them had a large hysteresis loop at partial load operation in the head/discharge characteristic curve, although the pump without them had no hysteresis loop. In the numerical simulation based on periodic flow, the incompressible turbulent flow field was calculated for partial blade-passages with periodic boundary conditions. As a result, the simulated characteristics had the same tendencies as the experimental results. Furthermore, the causes of the discontinuous head/discharge characteristics depending on the direction of partial load operation were clarified through calculating and comparing the internal flow fields in the cases with/without the fins. The pumps had the large backflow and recirculation areas in two places, one of which was near the shroud at the impeller inlet including the fins area and another near the central part of the diffuser. The difference in the hysteresis loop between with and without the fins was caused by the existence of the fins, which suppressed or promoted the backflow at the impeller.
Three-Dimensional Flow Analysis and Improvement of Slip Factor Model for Forward-Curved Blades Centrifugal Fan
Authors: Guo En-Min , Kim Kwang-Yong
Published: February 2009

The objective of this work is to develop improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan by investigating the validity of various slip factor models. Both steady and unsteady three-dimensional CFD analyses were performed with a commercial code to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the presented model takes into account the effect of blade curvature. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.
Pressure Correction on Unstructured Meshes Using High Order Convective Modelling
Authors: Charlesworth David J. , Zangeneh Mehrdad
Published: February 2009

A cell centred, finite volume, pressure correction method for unstructured grids is presented that facilitates the use of high order convective modelling. This is achieved through the use of a least squares technique to calculate first and second partial derivatives of the governing equations dependent variables. These derivatives are then used to construct both second and third order convective models that are bounded, accurate and stable. As an initial test of the effectiveness of these models calculated results are compared with standard laminar flow problems in both two and three dimensions.
Two-Phase Flow Analysis With the Two-Fluid MPS Method: I — Analysis of the Forced Convection Boiling
Authors: Horie Hideki , Yamamoto Yuichi , Shirakwa Noriyuki
Published: February 2009

A particle interaction method called MPS (the Moving Particle Semi-implicit method), which formulates the differential operators in Navier-Stokes’ equation as interactions between particles characterized by a kernel function, has been developed in recent years. We have extended this method to a two-fluid system with a potential-type surface tension in order to analize the two-phase flow without experimental correlation. This extended method (Two-Fluid MPS: TF_MPS) was successfully applied to a forced convection boiling experiment.
Computed Synovial Fluid Flow in a Simple Knee Joint Model
Authors: Pekkan Kerem , Nalim Razi , Yokota Hiroki
Published: February 2009

Prediction of shear stress induced by the fluid flow on knee joint cells is the main aim of this study. Oscillatory flow of a Newtonian synovial fluid is examined in two-dimensional joint geometries. The experimental model is a fluid driven shear loader test rig, which features a finite plate oscillating at 1Hz, that is 1mm over a stationary cell culture surface. Oscillating Couette flow in the thin gap is generated by the finite span plate. An incompressible two-dimensional transient and laminar CFD model is developed using the STAR-CD® code. The infinite oscillating plate Couette flow solutions (Stoke’s Second Problem with a finite gap) are reviewed and used in the grid sensitivity and validation tests of the computational finite oscillating plate model. The resulting flow features and vorticity convection are discussed and shear stress induced on the stationary plate due to an oscillating finite plate is compared with its infinite counterpart. As an extension, the effect of articular cartilage curvature is studied in a topologically equivalent model with and without menisci.
CFD Modeling Predictions of Near Burner Jet Region and Comparison With Sandia Flame
Authors: Mehrotra Vibhor , Berkoe Jonathan , Rawat Rajesh , Smith Phillip J.
Published: February 2009

Quantitative emissions prediction in industrial process furnaces is as difficult as it is important. A wide range of length and time scales must be bridged to capture the flow physics and chemistry of combustion and pollutant formation. This paper focuses on gathering and testing the state of the art for turbulence, mixing and reaction subgrid scale (SGS) models as they are applied to the near burner region using a commercial CFD code. The Fluent® version 5.5 computational fluid dynamics (CFD) code is used to simulate a single port, axisymmetric fuel jet of 50% (by vol.) methane and 50% hydrogen in a co-flowing air stream (Sandia flame HM1a). This configuration is chosen for its simplicity and for the wealth of experimental data available [1]. The intermediate goal is to predict temperature and species concentration accurately that may affect the prediction of NO concentrations in the flue products. Therefore, flow dynamics, heat transfer; combustion and NOx chemistry are important issues and will be analyzed in this paper.
Quasi-Linear Theory of Ship Wave Resistance and CFD Analysis of Ship’s Environmental Impact
Authors: Amromin Eduard , Kovinskaya Svetlana , Mizina Marina , Mizine Igor
Published: February 2009

Quasi-linear theory (QLT) introduces corrections to the Havelock integral and makes it possible to operate with realistic wave amplitudes and length into framework of linear theory. These corrections for wave amplitude and length are based on implicit employment of the model 2D problems for nonlinear waves of highest magnitude (Stokes waves). There is both description of algorithms and comparison with towing test results for diverse ships here. A substantially novel (and environmentally important) aspect of this paper is application of QLT to computation of ship wave resistance in shallow waters.
Numerical Simulation to Determine the Heat Transfer Coefficient in the Boiling Phenomenon of Run-Out Table of a Hot Strip Mill
Authors: Sikdar S. , Mukhopadhyay A.
Published: February 2009

A Mathematical model has been developed to predict the temperature profile of the strip in the Run-out Table (ROT) of the Hot Strip Mill (HSM) at Tata Steel, India. The prediction of temperature profile across the thickness of the strip shows good results. A simple correlation for heat transfer coefficient has emerged from this study. A polynomial as a function of strip surface temperature has been found to represent the heat transfer coefficient at water-strip interface accurately. The salient features of this paper are described as follows: 1) An off-line model has been developed to predict the through thickness temperature of the strip in the Run-out Table of a Hot Strip Mill. 2) The heat transfer coefficient at water-strip interface on the water-cooled zone over the bed of Run-out Table can be considered as a polynomial of strip surface temperature. Tests have been performed to validate the correlation of heat transfer coefficient against several thousand coils.
Comparison Between a Slot Jet and Round Jets Impinging a Curved Wall
Authors: Gilard V. , Brizzi L.-E.
Published: February 2009

Velocity measurements by PIV are realized in order to compare a slot jet and round jets impinging a curved surface. A statistical data processing allows us to obtain the mean velocity fields and the Reynolds stresses. For the two jet geometries, the flow structure is described. Some velocity distributions according to different axis are extracted of the mean velocity fields and are also described.
Study on Characteristics of Thermal Flow-Induced Vibration in Unlooped Heat Pipe
Authors: Saeki Souichi , Fujinaka Shinichi , Ogawara Kakuji
Published: February 2009

In this paper, presented is an experimental study of thermal flow-induced vibration in a both-ends-closed type self-induced oscillating heat pipe. This was made of winding glass tube to visualize the phenomenon. It was heated at the bottom to control temperature by heater, while was cooled at the top to keep temperature constant. Liquid column oscillation was excited with boiling and expansion of vapor plug. When liquid volume fraction was large, the magnitude of pressure oscillation was large and low frequency was relatively dominant. Furthermore, normalized temperature θt was proposed to investigate the threshold of excited conditions, taking account of initial condition, e.g. initial pressure. With respect to liquid volume fraction, θt was alternately varied up and down. This phenomenon was evaluated to be dependent on the liquid volume fraction.
Numerical Simulation of the Hole-Tone Feedback Cycle Based on the Discrete Vortex Method and the Acoustic Analogy
Authors: Langthjem Mikael A. , Nakano Masami
Published: February 2009

An axisymmetric numerical simulation approach to the holetone feedback problem is developed. It is based on the discrete vortex method and an ‘acoustic analogy’ representation of flow noise sources. The shear layer of the jet is represented by ‘free’ discrete vortex rings, and the jet nozzle and the end plate by bound vortex rings. A vortex ring is released from the nozzle at each time step in the simulation. The newly released vortex rings are disturbed by acoustic feedback. The simulated frequencies f follow the criterion L/uc + L/c0 = n/f where L is the gap length, uc is the shear layer convection velocity, c0 is the speed of sound, and n is a mode number (n = 1/2, 1, 3/2, ...). This is in agreement with experimental observations. The numerical model also display mode shifts (jumps in the chosen value of n), as seen in experiments.
Effect of Reynolds Number on the Unsteady Flow and Acoustic Fields of Supersonic Cavity
Authors: Hamed A. , Basu D. , Das K.
Published: February 2009

Numerical simulations are conducted to study the flow and acoustic fields for unsteady supersonic turbulent flow over an open cavity using Detached Eddy Simulations for two different Reynolds numbers. Results are presented for pressure fluctuations history, vorticity iso-surfaces and turbulent kinetic energy and sound pressure levels spectra. The results reveal higher sound pressure levels (SPL), and finer scale structures within the cavity at the higher Reynolds number.
Simple Experiments of Fluids Possible in Classrooms or at Home
Authors: Hasegawa Tomiichi
Published: February 2009

Fluid mechanics concerning Newtonian fluids has been established and the fundamental equation has been analyzed theoretically or with computers. But sometimes the problems encountered in industries or laboratories are too complicated to be solved by theoretical or computational analyses, so that experiments become important. Furthermore, experiments are very fruitful for beginners to feel the motion of fluid actually. This report presents a few methods for the aim that undergraduates do simple experiments in their class or at their homes. One method is a measurement of the drag coefficient of a cylinder by use of a tissue paper. The other method is to feel a lift by use of a spoon and the city water issuing out of a faucet and estimate the coefficient of lift by utilizing the law of momentum.
Experiment of Flow-Induced Vibration Phenomenon in Undergraduate Student Experimental Class
Authors: Takahashi Tsutomu , Shirakashi Masataka
Published: February 2009

The fluid engineering experiment class for undergraduate students in Nagaoka University of Technology is explained. Students learn the fundamental theory of the flow-induced vibration by teacher’s lecture and the video program in class room and move to the experiment room. They play with some simple device that is designed to cause the phenomenon of the flow-induced vibration. It is not difficult to cause the flow-induced vibration phenomenon on the devices but a few training and knacks are necessary. These devices were made by us for this experiment. Controlling the oscillation of these devices is interesting and it excites students so that we call them toys. Students learn the influence of various factors that cause the occurrence of the resonance and the fluttering through this experience. After this experience, they start more accurate and systematic experiment using the wind tunnel equipment. They write the report, and discuss their experiment result. We explain the details of these student experiment class and demonstrate the toys for the flow-induced vibration phenomenon.
Measurement of Solids Concentration in Slurries Using Electrical Impedance Spectroscopy Technique (Keynote)
Authors: Hu Shenggen , Firth Bruce
Published: February 2009

In this research work, an electrical impedance spectroscopy technique has been developed to measure the solids concentration of slurry mixtures. This new measurement technique is based on the fact that the AC frequency responses of solids are distinct from those for the liquid phase. In this technique, the electrical impedance spectrum of slurry mixtures is measured over the frequency range of 0.1 Hz to 1 MHz. Changes in the frequency response at different excitation signal amplitudes reflect changes in the slurry composition and the electrical conductivity of the liquid phase, and by analyzing the spectra using artificial intelligence data analysis techniques, such as Multiplayer Perceptron Artificial Neural Network, one can determine the volumetric fraction of the solids phase. The technique has been successfully tested for various slurries under different conductivities of liquid phase and temperatures. In contrast with previous techniques based on conductivity or capacitance, this new technique can be used for on-line measurement of solids concentration in slurry streams even when the conductivity of the liquid phase changes substantially with time.
Turbulence Structure of a Liquid-Solid Two-Phase Jet by Means of Laser Techniques
Authors: Arai Toshimichi , Kudo Naoki , Ishima Tsuneaki , Youssef Ismail M. , Obokata Tomio , Abdel-fadeel Waleed A.
Published: February 2009

Characteristics on particle motion in a liquid-solid two-phase jet flow were studied in the paper. The water jet including glass particle of 389 μm in mean diameter was injected into water bath. The experimental conditions were 0.21% of initial particle volume ratio, 5mm in pipe diameter and 1.84 m/s of mean velocity on outlet of the jet. A laser Doppler anemometer (LDA) with size discrimination was applied for measuring the time serious velocities of the single-phase flow, particle and water phase flow. A particle image velocimetry (PIV) was also applied in the two-phase flow. The normal PIV method can hardly measure the particle size and perform the particle size discrimination. In the experiment, using the gray scales related with the scattering light intensity, measuring method with size discrimination in two-phase flow was carried out. The experimental results show less difference between velocities of single-phase flow and water-phase flow under this low particle volume ratio condition. Particles have the relative motion with the water-phase and large rms velocity. The PIV used in this experiment, which is called multi-intensity-layer-PIV: MILP, can measure water-phase velocity with good accuracy.
Particulate Velocity Measurements in the Intra-Blade Passages of a Centrifugal Slurry Pump
Authors: Kadambi J. R. , Mehta M. , Charoenngam P. , Wernet M. P. , Sankovic J. , Addie G.
Published: February 2009

The purpose of a slurry pump is to transport solids in a mixture called a slurry. It is a critical component of the slurry transport system in many industrial and mining related processes. In this investigation, Particle Image Velocimetry (PIV) was successfully utilized for measuring the particle velocities in the impeller intra-blade passages of an optically clear centrifugal pump (a transparent casing and a transparent three-blade impeller). An optically clear slurry consisting of sodium-iodide solution and 500 μm spherical glass particles was used. The experiments were conducted at speeds of 725 and 1000 rpm with volumetric concentrations of 2.5% and 5% respectively. In the impeller passage region, the highest particle velocities are generated on the suction side of the blade and in the blade trailing edge region as the blade sweeps through. However, these particle velocities are slower than the circumferential velocity of the blade tip. The particle fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The maximum fluctuation kinetic energy occurred on the suction side of the blade. The directional impingement mechanism is more significant at the pressure side of the blade. This mechanism becomes more pronounced as the speed increases. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the blade surface (pressure and suction sides) and the casing wall erosion. Frictional wear mechanisms can be caused by the particles that do not stay suspended in the flow and accumulate into sliding beds along the pressure side of the blade. PIV measurements in the slurry pump model can add significantly to the understanding of the flow through the pump.
Vortex Induced Auto-Rotation of a Hinged Plate: A Computational Study
Authors: Seshadri Veeraraghavan , Mittal Rajat , Udaykumar H. S.
Published: February 2009

Numerical simulations have been used to study the phenomenon of autorotation of a flat plate hinged about its center in a freestream. The focus of the paper is on examining the effect of Reynolds number and plate thickness ratio on vortex induced rotation. The numerical solver employed is based on a sharp interface, Cartesian grid method that allows us to simulate flow with moving boundaries on stationary Cartesian grids. Simulations indicate that vortex shedding is the primary instigator of the plate motion and the transition from fluttering to autorotation depends on both these parameters.
Numerical Simulation of Conducting Fluid Flow With a Largely Deformed Free Surface Under Alternating Magnetic Field
Authors: Kohno Haruhiko , Tanahashi Takahiko
Published: February 2009

A new numerical scheme for the analysis of conducting fluid flow under the alternating current magnetic field is presented. In this scheme, the large deformation problem of a free surface is stably calculated by using LSM (level set method), and the computation of the electromagnetic field is economically carried out by discretizing the governing equations formulated by a vector potential method with hybrid FEM-BEM (finite element method – boundary element method). Two-dimensional numerical simulation in terms of the oscillation of a conducting drop set between two coil sections under non-gravity is conducted to verify the effectiveness and robustness of the present scheme. As a result, the oscillatory behavior is successfully obtained from the interaction between the Lorentz force and the restoring force. It is confirmed that the amplitude and the periods in the oscillation depend on the effective value of the alternating current flown in a coil and the magnitude of surface tension. Moreover, some numerical results obtained here agree with theory.
A Numerical Algorithm Based on a Tree Data for an Anisotropically Adaptive Cartesian Mesh
Authors: Ogawa Takanobu
Published: February 2009

In an adaptive Cartesian mesh approach, a rectangular mesh is recursively and locally refined and mesh can be automatically generated for complex flow geometry. In this study, a numerical algorithm is developed for an adaptive Cartesian mesh. The tree data is employed to organize the adaptively refined meshes. With this data structure, mesh adaptation becomes very flexible and the algorithm developed for a conventional flow solver can be adapted with less modification. The algorithm can be extended for the anisotropic mesh refinement which is efficient for a boundary layer problem. Parallelization of the developed algorithm is also done in the SPMD paradigm. The domain decomposition technique is used and a tree data structure is split so that computational load should be balanced. Parallel efficiency is examined on a PC cluster.
The State-of-the-Art of Gas-Liquid Compact Separator Control Technology: From Lab to Field
Authors: Wang Shoubo , Gomez Luis , Mohan Ram , Shoham Ovadia , Kouba Gene , Marrelli Jack
Published: February 2009

Conventional gas-liquid separators are vessel-type with simple level, and pressure control since the residence time is large. Compact gas-liquid separators, such as Gas-Liquid Cylindrical Cyclone (GLCC©), have emerged recently as alternatives to reduce size and increase separation efficiency for offshore and subsea applications. As compared to the vessel-type separators, compact separators, are simple, low-cost, low-weight, require little maintenance and are easy to install and operate. However, the residence time of the GLCC is very small. Consequently, it can get upset easily due to high flow variations at the inlet, for example, slugging, without the aid of fast and accurate control systems. In the past, lack of understanding of control system dynamics and design tools have prevented this technology from fast field deployment. The objective of this study is to present a review of the compact gas-liquid separator (GLCC) control technology. This includes the development of control strategies, control system design, dynamic simulation, experimental investigation and field applications. The performance of compact gas-liquid separator (GLCC) strongly depends on the liquid level and/or separating pressure. In this investigation, several control strategies have been developed for field applications of gas-liquid compact separators. Especially, an optimal control strategy was developed for handling slug flow and optimizing the system performance in terms of reduced or eliminated liquid carry-over (LCO) or gas carry-under (GCU). The developed strategies have been used for the design of several GLCC applications, currently in operation in the field. Details of these applications are also presented. This study provides the state-of-the-art of gas-liquid compact separator control technology from the lab to field.
Measurement of Gas/Liquid Flow Velocities in Rapidly Rotating Annular Systems
Authors: Aroussi Abdelwahab , Ishaq Gazala , Menacer Mohammed
Published: February 2009

To help understand the behaviour of oil/gas mixtures and the lubrication processes within bearing chambers of an aero-engine, a rig was developed to represent the bearing chamber at a simplified level. The velocities of gas and liquid flow prevailing around the rapidly rotating annulus were explored when exposed to various parametric conditions. The results revealed that the liquid flowrates, aerodynamic forces and shaft rotation speeds affect the phenomena of gas/liquid flows. Changes in these conditions profoundly affect the behaviour of the lubricating jet, the sizes of the liquid droplets and their velocities as well as the liquid films. These, consequently influence the heat transfer and lubrication mechanisms within annular systems.
Comparison of Near Wake-Flow Structure Behind a Solid Cap With an Attached Bubble and a Solid Counterpart
Authors: No Hidekazu , Call Michel , Tokuhiro Akira T.
Published: February 2009

An experimental study was conducted on the flow structure in the near-wake of a hollow cap with an air bubble attached underneath and a solid object possessing a bubble-like shape. The objective of the study was to elucidate distinguishing wake flow characteristics of the capped bubble relative to the solid. The experiment was performed in a square channel, 80×80mm2 in cross section. The bubble and solid were separately suspended in downward flow of purified water. Both the capped bubble and the solid were ellipsoidal in shape (the cap was shaped to represent the front of an ellipsoidal bubble) and had an approximate volume of 0.8ml. The Reynolds number for the flow, based on the objects’ equivalent diameter and average downward flow velocity (U = 25cm/s), was Re ≅ 2800. Velocity measurements were taken using Particle Image Velocimetry. The obtained velocity data were analyzed to deduce vorticity, turbulent kinetic energy, production, and Reynolds stress. Graphic and numerical comparisons between the two cases were made. The results to date are discussed.
Study for the Gas Flow Through a Critical Nozzle
Authors: Kim Heuy Dong , Kim Jae Hyung , Park Kyung Am
Published: February 2009

The critical nozzle is defined as a device to measure the mass flow with only the nozzle supply conditions, making use of flow choking phenomenon at the nozzle throat. The discharge coefficient and critical pressure ratio of the gas flow through the critical nozzle are strongly dependent on Reynolds number, based on the diameter of nozzle throat and nozzle supply conditions. Recently a critical nozzle with small diameter is being extensively used to measure mass flow in a variety of industrial fields. For low Reynolds numbers, prediction of the discharge coefficient and critical pressure is very important since the viscous effects near walls significantly affect the mass flow through critical nozzle, which is associated with working gas consumption and operation conditions of the critical nozzle. In the present study, computational work using the axisymmetric, compressible, Navier-Stokes equations is carried out to predict the discharge coefficient and critical pressure ratio of gas flow through critical nozzle. In order to investigate the effect of the working gas and turbulence model on the discharge coefficient, several kinds of gases and several turbulence models are employed. The Reynolds number effects are investigated with several nozzles with different throat diameter. Diffuser angle is varied to investigate the effects on the discharge coefficient and critical pressure ratio. The computational results are compared with the previous experimental ones. It is known that the standard k-ε turbulence model with the standard wall function gives a best prediction of the discharge coefficient. The discharge coefficient and critical pressure ratio are given by functions of the Reynolds number and boundary layer integral properties. It is also found that diffuser angle affects the critical pressure ratio.
Hydrodynamic Performance of the Large Cavitation Channel (LCC)
Authors: Park Joel T. , Cutbirth J. Michael , Brewer Wesley H.
Published: February 2009

The U. S. Navy William B. Morgan Large Cavitation Channel (LCC) in Memphis, Tennessee, is the world’s largest water tunnel. Its hydrodynamic performance is outlined in this paper. Three key characteristics of tunnel velocity were measured: temporal stability, spatial uniformity, and turbulence. Temporal stability and spatial uniformity were measured by laser Doppler anemometer (LDA), while the turbulence was measured with a conical hot-film and constant temperature anemometer (CTA). The velocity stability at a single point for run times greater than 2 hours was measured as ±0.15% at the 95% confidence level for velocities from 0.5 to 18 m/s. The spatial non-uniformity for the axial velocity component was ±0.34 to ±0.60% for velocities from 3 to 16 m/s. The non-uniformity in the vertical velocity was nominally 2%. The turbulence or relative turbulence intensity, which is the commonly reported performance characteristic for water tunnels, was measured as 0.2 to 0.5% depending on tunnel velocity. Additional information includes calibration of the LDA and CTA, test section velocity as a function of pump speed, acceleration of the test section velocity, velocity spectra, and color contour plots of the axial and vertical components for velocity uniformity. The measurements demonstrate that the LCC is a high-quality world-class water tunnel.
Computation of Rotor/Stator Interaction With Hydrogen-Fuelled Combustion
Authors: Sato Masanori , Nagumo Takashi , Toda Kazuyuki , Yamamoto Makoto
Published: February 2009

For the next-generation aircraft, a new propulsion system using hydrogen fuel has been proposed. In the present system, hydrogen fuel injected from a stator surface combusts in the turbine passages, accordingly, the conventional combustor can be cut out. The advantage of this system is that we can design a lighter and smaller engine with low emission. We have demonstrated the realizability of this system by using the cycle analysis and the numerical simulations. Through the previous studies, it was confirmed that the rotor/stator interaction has to be investigated, because the hydrogen combustion phenomena within the stator passage is so complex, and thus it would highly affect the rotor performance. In this paper, we focus on the rotor/stator interaction for the detailed investigation of realizability of this system. The 2- and 3-dimensional numerical simulations are performed for a single stage turbine with hydrogen-fuelled combustion. In the 2-dimensional study, the effects of the injection position and injection rate on the flow structure, the static temperature over the blades, and the blade performance are investigated. Furthermore, 3-dimensional numerical simulation is performed. The general aspect of 3-dimensional flow field is demonstrated, and the effect of hydrogen combustion on the components of turbine, for example hub, tip and blade, are investigated.
Experimental Study on the Performance and Flow Characteristics of a Small Horizontal Axis Wind Turbine (HAWT)
Authors: Gutierrez Isaac , Okajima Atsushi , Kiwata Takahiro , Kimura Shigeo , Wakisaka Yoshitaro
Published: February 2009

With the aim of getting basic data to increase the efficiency of a small horizontal axis wind turbine (HAWT) systems, the wind tunnel experiments were carried out to observe flow characteristics of rotating blades of the turbine, using the oil-film visualization technique, and to measure turbine performance. Flow visualization allowed the identification of laminar flow, laminar separation bubble formation, flow reattachment, turbulent boundary layer, and turbulent separation. The complex patterns on the rotating blade surface were confirmed by the oil-film visualization method and identified. When the trip-tape was employed for control of the blade boundary layer, the efficiency was not significantly improved. Field-tests of this turbine were performed also, and averages of wind speed and net power were calculated from the field measured data using the bins method and were compared with wind tunnel performance tests. The results of field-tests showed for this small HAWT that the highest power coefficient value was 30%.
Control of Compressible Dynamics Stall Using Microjets
Authors: Shih C. , Beahn J. , Krothapalli A. , Chandrasekhara M. S.
Published: February 2009

Control of the dynamic stall process of an NACA 0015 airfoil undergoing periodic pitching motion is investigated experimentally in a high-speed wind tunnel facility. Multiple microjet nozzles distributed uniformly in the first 15% chord from the airfoil’s leading edge are used for the control. Point Diffraction Interferometry (PDI) technique is used to characterize the control effectiveness, both qualitatively and quantitatively. The microjet control has been found to be very effective in suppressing both the emergence of the dynamic stall vortex and the associated massive flow separation at the entire operating range of angles of attack. At the high Mach number case (M = 0.4), the use of microjets appears to eliminate the shock structures that are responsible for triggering the shock-induced separation, establishing the fact that the use of microjets is effective even in controlling dynamic stall with a strong compressibility effect. In general, microjet jet control has an overall positive effect in terms of maintaining leading edge suction pressure and preventing flow separation.
Curvature Effects in the Curved Duct for the Compressible Viscous Flow With Heat Transfer
Authors: Ozaki Kougen , Maekawa Hiroshi
Published: February 2009

In this paper, non-reflecting boundary conditions based on the NSCBC method for three-dimensional compressible viscous flows, especially outlet boundary conditions, are examined and numerical tests for a curved duct flow are made. Using the subsonic non-reflecting outflow boundary conditions, curvature effects for compressible flow are investigated. First, numerical flows in a straight duct was tested for the stability of the solution and the efficiency of the subsonic non-reflecting outflow conditions extended to 3D problems. Numerical tests show that the non-reflecting NSCBC method provides accurate results for very low Reynolds number flow with isothermal no-slip walls. Second, the unsteady Navier-Stokes equations in cylindrical coordinates were numerically solved using the non-reflecting outflow conditions for a curved duct flow with isothermal no-slip walls. The numerical results show the consistency of the solution. Finally, analyzing the curved duct flow results, effects of the duct curvature were studied. A comparison of the numerical results between two curved ducts, the curvature is 102 times larger than smaller one, shows that the maximum intensity of secondary flow appeared at the outlet section of the more curved duct is about 102 times larger.
On Numerical Prediction of the Stability of Hypersonic Boundary-Layer Flow Over a Row of Microcavities
Authors: Theofilis Vassilios , Deville Michel O. , Duck Peter W. , Fedorov Alexander
Published: February 2009

This paper is concerned with the structure of steady two–dimensional flow inside the viscous sublayer in hypersonic boundary–layer flow over a flat surface in which microscopic cavities (‘microcavities’) are embedded. Such a so–called Ultra Absorptive Coating (UAC) has been predicted theoretically [1] and demonstrated experimentally [2] to stabilize passively hypersonic boundary–layer flow. In an effort to further quantify the physical mechanism leading to flow stabilization, this paper focuses on the nature of the basic flows developing in the configuration in question. Direct numerical simulations are performed, addressing firstly steady flow inside a singe microcavity, driven by a constant shear, and secondly a model of a UAC surface in which the two–dimensional boundary layer over a flat plate and a minimum nontrivial of two microcavities embedded in the wall are solved in a coupled manner. The influence of flow– and geometric parameters on the obtained solutions is illustrated. Based on the results obtained, the limitations of currently used theoretical methodologies for the description of flow instability are identified and suggestions for the improved prediction of the instability characteristics of UAC surfaces are discussed.
Numerical Investigation on Suppression of 3-Dimensional Shock Wave/Turbulent Boundary Layer Interaction by Passive Cavity
Authors: Toda Kazuyuki , Dambara Shinsuke , Yamamoto Makoto , Honami Shinji , Akahoshi Nobuyuki
Published: February 2009

Suppression of three-dimensional shock wave/turbulent boundary layer interaction is one of the important subjects on supersonic air intake. In the present study, the passive control of 2- and 3-dimensional shock wave/turbulent boundary layer interactions is considered. First, computations are performed for two-dimensional flow field at freestream Mach number of 2.46 with various passive cavities beneath the interaction region. The results suggest that the parallel blowing from a cavity to the mean flow with a guide plate can highly keep the interaction region narrow. Next, the most suitable cavity shape clarified in the 2-dimensional computations is applied to the 3-dimensional swept shock wave/turbulent boundary layer interaction at Mach number of 3.11. It is exhibited that the blowing direction is important, and the effect of passive cavity is nearly the same as the bleeding.