bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Studies of Liquid Crystalline Flow Induced by Annihilation of Paired Defects
Authors: Kuroiwa Masahiro , Tsuji Tomohiro , Chono Shigeomi
Published: March 2009

Numerical and experimental studies of liquid crystalline flow induced by the annihilation of paired defects have been achieved by using the Doi theory coupled with the Marrucci-Greco potential. The molecular orientation distribution function is approximated by a series of spherical harmonic functions, to reduce the computational task. It is empirically known that the defects with different types of molecular orientation configuration attract each other, and finally annihilate. During this annihilation process, the liquid crystalline flow will be induced through the rotation of the molecular orientation direction. It is found from the numerical results that vortex-like liquid crystalline flow is induced around the defects come closer. The numerical predictions are induced liquid crystalline flow is confirmed by the experiment.
Bubble Generation in the Micro-Channel With a Barrier
Authors: Xiong Renqiang , Bai Mo , Na Yun Whan , Chung Jacob N.
Published: March 2009

Micro-bubble generation in a rectangular co-flowing micro-channel with a cross-section area of 1.69 × 0.07mm2 was experimentally and numerically investigated. Air and water were used to be the gas and liquid, respectively. Mixtures of water-glycerol and water-Tween 20 were also used to obtain the effect of viscosity and surface tension. The experimental data shows that the break-up process is periodic under certain operating conditions. The bubble dynamics are also examined using a computational fluid dynamics (CFD) simulation. The CFD model successfully simulates the flow behavior and provides a closer examination of the bubble shape. The bubble length L to the channel width w is a function of the ratio of gas flow rate Qg and liquid flow rate Ql which is the same as that used in the T-junction. Bubble frequency f is found to be related with channel width w, channel depth h, and QlQg/(Qg + Ql · π/4). The formulation shows good agreement with the experimental data at the low frequency region. Different bubble shapes can be obtained at different liquid viscosities and surface tensions. The dimensionless bubble length L/w can still be predicted by a modified equation which uses the real bubble width wb or an equivalent bubble length Le.
Visualizing Fluid Flows With X-Rays
Authors: Heindel Theodore J. , Jensen Terrence C. , Gray Joseph N.
Published: March 2009

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.
Development and Validation of an ALE-Based Airbag Simulation Methodology
Authors: Yeh Isheng , Zhou Rongrong , Cheng James , Olovsson Lars , Wang Jason
Published: March 2009

For the past fifteen years, automotive safety engineers have mainly relied on the Control Volume (CV) approach to simulate airbag deployment. The CV approach assumes that the gas is uniformly distributed in an inflated bag and therefore the airbag fabric is subject to uniform pressure. This assumption is true only when the airbag is fully deployed, and therefore makes CV approach inappropriate for Out-of-Position (OOP) safety analysis in which an occupant is in close proximity to the air bag module when it deploys, and therefore airbag-occupant interaction occurs before the bag is fully inflated. This paper describes the theory and validation of a new airbag simulation tool, an ALE-based (Arbitrary-Lagrange-Eulerian) approach. This tool, developed by Livermore Software Technology Corporation (LSTC), is aimed at using ALE as a CFD (Computational Fluid Dynamics) tool to model the gas flow inside a deploying airbag and the interaction between the airbag and the inflator gas. The validation of this methodology is performed through comparing the simulation results with test results of various test setup and airbag design.
Cavitation Inception Behind a Jet-Propelled Body
Authors: Hambleton William , Amromin Eduard , Arndt Roger E. A. , Kovinskaya Svetlana
Published: March 2009

Cavitation inception behind an axissymmetric body driven by a waterjet has been studied experimentally and numerically. Water tunnel tests have been performed with the body mounted on a force balance. The transom of the body contained a nozzle located along the centerline. Tests were carried out for various water tunnel speeds such that jet velocity ratio, VJ/U, could be varied in the range 0 to 2. Distinctly different cavitation patterns were observed at zero jet velocity (when cavitation appeared in spiral vortices in such flows) and at a various jet velocity ratios (when cavitation appeared between counter-rotating vortices around the jet in such flows). Cavitation inception/disappearance has been determined visually. The body drag was also measured. An analytical method for determination of cavitation inception index has been developed on the basis of a viscous-inviscid interaction concept, with employment of special semiempirical approximations for vortices and consideration of surface tension. These approximations have been preliminarily validated for nozzle jet cavitation (for nozzle discharge in co-flow). It was assumed that visualization allows detection of cavities (bubbles) of 0.4mm-0.5mm diameter or larger. The cavitation inception index is defined as the cavitation index for cavities of such minimum diameter when these cavities are located between counter-rotating vortices. The initial comparison of predicted and measured values of the cavitation inception index shows good agreement.
Numerical Simulation of Sand Erosion Phenomena in Square-Section 90 Degree Bend With Linear/Nonlinear RANS Turbulence Models
Authors: Suzuki Masaya , Inaba Kazuaki , Yamamoto Makoto
Published: March 2009

Sand erosion is a phenomenon where solid particles impinging to a wall cause serious mechanical damages to the wall surface. This phenomenon is a typical gas-particle two-phase turbulent flow and a multi-physics problem where the flow field, particle trajectory and wall deformation interact with among others. On the other hand, the sand erosion is a serious problem to install pneumatic conveying systems for handling abrasive materials. Incidentally, the bend erosion is typical target of sand erosion experiments and is useful for verification of numerical simulations. Although, the secondary flow which occurs in such a flow field including streamline curvature cannot be reproduced by the standard k-ε model. To predict this flow field, a more universal model which can estimate anisotropic Reynolds stress is required. In the present study, we simulate sand erosion of 90 degree bend with a square cross-section. We use some linear/nonlinear turbulence models to predict the secondary flow of the bend. Besides, the performance of each model to predict clear/eroded bend flow field is studied.
Experimental and Numerical Investigation of Cavitation Regimes and Its Effects on Drag Characteristics of Wedge Shaped Bodies
Authors: Osta M. , Mansouri H. , Razmi A. M. , Amini M. A.
Published: March 2009

Cavitation phenomenon is defined as the process of rupturing any liquid by a decrease in pressure at nearly constant temperature. The cavities driven by the flow in a region of high pressure will implode and generate high pressure pulses leading eventually to erosion and vibration. But in supercavitation the bubbles produced by cavitation combine to form a large, stable bubble region around the supercavitating object. This phenomenon decreases the drag on the supercavitating body. Experimental testsware performed at 2-D unsteady flow for two wedge shaped bodies made before in laboratory and cavitation inception and its development were captured by a high speed camera. Then this cavitation regime around the wedge was studied numerically. In these cases CFD code was developed to simulate the unsteady and incompressible flow based on finite volume, 2D transient, with different boundary conditions. These numerical models which were evaluated experimentally depicted the capabilities of this CFD code to simulate this flow field cavitation inception, its development, and drag force in all cases. In this study we worked on two different geometries. Whether the cavitation is occurred at nose of body or not is worthy and studied by the above mentioned scheme. Moreover, we wanted to find the supercavitation regime and drag reduction for these two bodies.
Pressure Drop Prediction Considered Fluidized Particle in Vertical Plug Transportation
Authors: Kofu Kenji , Ochi Mitsuaki , Takei Masahiro
Published: March 2009

The prediction equations on particle velocity within a plug and pressure drop in vertical pipe have been formulated by considering fluidized particles. The gas-liquid two-phase theory established by Davidson and Harrison has been assumed as fluidized particles. As a result, the all kinds of calculated values on particle velocity and pressure drop are in good agreement with the experimental values while internal pipe diameter and kinds of particles are changed. The error between calculations and experiments is almost within ± 10%. Additionally, the plug velocity and particle velocity in the flow and radius directions have been measured by digital video camera, high speed camera and PIV. As a result, gas-liquid two-phase theory can be applied to the relation between plug velocity and particle velocity, and there is no particle velocity distribution in the plug. In short, particles in the plug are fixed relative to each other and so they all move with the same velocity.
Particle Velocities in the Rotating Impeller of a Slurry Pump
Authors: Mehta M. , Kadambi J. R. , Sastry S. , Sankovic J. M. , Wernet M. P. , Addie G. , Visintainer R.
Published: March 2009

The velocities of the slurry particles in the impeller of a centrifugal slurry pump were obtained utilizing Particle image velocimetry (PIV) technique in conjunction with refractive index matching. Tests were performed in an optically clear centrifugal slurry pump at speeds of 725 rpm and 1000 rpm using a slurry made up of sodium iodide solution as a working fluid and glass beads (500μm mean diameter) as solid particles at volumetric concentrations of 1%, 2%, and 3%. In the intra blade region of the impeller, the highest particle velocities were obtained in the suction side of the blade and in the blade trailing edge region as the blade sweeps through and velocity magnitude increases with the increase in the pump speed. But this magnitude was less than that of circumferential velocity of the blade tip. The average particle velocities were obtained and it was found that the average particle velocity decreases with increase in concentration. The fluctuating component of particle velocity, which is related to the fluctuation kinetic energy were obtained. With the increase in the particle volumetric concentration, fluctuation kinetic energy decreases and the maximum fluctuation kinetic energy typically occurs on the suction side of the blade. The slurry particles are pushed on the pressure side of the blade and slide on it which can result in frictional wear. These results are discussed in this paper.
Numerical Simulation of Fluid Flow and Oxygen Transport in the Tube Flow Cells Containing Biofilms
Authors: Salek M. , Martinuzzi R. J.
Published: March 2009

The hydrodynamics in flow systems is known to induce phenotypic changes associated with bacterial biofilms, including increased tolerance to antimicrobial agents and biocides. Results obtained in flow cells commonly used in biological and medical studies on the influence of flow on biofilm behavior and antimicrobial susceptibility are sometimes contradictory. It is thus hypothesized that discrepancies in the results may be related to the flow cell geometry. In this study, the shear stress distribution and substrate concentration were numerically simulated inside long rectangular and square tubes. The fluid was Newtonian and a uniform distribution of biofilms, which consume the substrate from the medium, was assumed on the walls. The consumption of oxygen by biofilms was assumed to follow the Monod kinetics. The effects of flow velocity, flow cell geometry, and substrate diffusivity on wall shear stress and substrate concentration distributions were investigated. Based on simulation results, differences observed in the morphology and response of biofilms can be directly related to hydrodynamic changes caused by the flow cell configuration.
Application of a Vortex Method to Fluid Dynamics in Sports Science
Authors: Kamemoto Kyoji , Ojima Akira
Published: March 2009

This paper describes a pioneering work of practical application of an advanced vortex method in the field of fluid dynamics in sports science. The vortex method developed by the present authors is one of vortex element methods based on the Biot-Savart law, and it is known that the method provides a Lagrangian simulation of unsteady and vortical flows. In this study, in order to examine the applicability of the vortex method, three-dimensional, complex and unsteady flows around an isolated 100 m runner and a ski-jumper were calculated. Basic equations and mathematical treatment of the method are explained in this paper, and calculation conditions and panel data of deforming configuration of the athletes are described. As results of the present study, vortical and unsteady flow features around a runner and a ski-jumper are understood, and unsteady variation of aerodynamic forces corresponding to deformation of body configuration due to athletic motion are calculated. And, it is confirmed that the advanced vortex element method is a promising way to a grid-free Lagrangian large eddy simulation of unsteady and complex flows around dynamic bodies of athletes.
Effects of Geometrical Structure on Flows Around a Rotating Disk in an Enclosure
Authors: Watanabe T. , Furukawa H. , Suzuki M.
Published: March 2009

Flows around a rotating disk in a cylindrical enclosure are typical models of flows found in fluid machinery and chemical reactors. They have their practical applications and draw engineering interests. When the radius of the disk is infinite, it is known that circular rolls, spiral rolls, turbulent spirals and turbulent spots appear. In this case, the parameters governing the flows are the Reynolds number based on the angular velocity of the disk and the axial gap between the disk surface and the end wall of the enclosure. We consider, in this paper, a more practical configuration. The disk has its thickness comparable with the axial height of the enclosure, and the radial gap between the disk rim and the side wall of the enclosure is not negligible. Vortex flows are driven by the centrifugal force around the disk rim, and they are expected to have effects on the entire flow. We performed numerical and experimental studies and investigated the unsteady three-dimensional behaviors. A new criterion to identify flow patterns is introduced and the Hopf bifurcation points from the axisymmetric flows to the three-dimensional flows are determined. The phase velocity of the spiral rolls are measured by a time-dependent analysis. The influence of the geometrical structure on the phase velocity is estimated. New types of flows are found, where bead-like vortices appear and spiral rolls with positive and negative front angles coexist.
Experimental Investigation of Flow Field Structure in Non-Isothermal Mixing Tee
Authors: Hosseini Seyed Mohammad , Yuki Kazuhisa , Hashizume Hidetoshi
Published: March 2009

T-junction is one of familiar components in the cooling system of power plants with enormous capability to high-cycle thermal fatigue. This research tries to investigate fluid mixing mechanism in non-isothermal T-junction area with 90-degree bend upstream. Classification of turbulent jet and effects of 90-degree bend were evaluated previously and re-attached jet was selected as complicated mixing structure with highest velocity fluctuation [4]. For considering the mixing mechanism of re-attached jet, T-junction area is visualized in various lateral and longitudinal sections. The measuring data show the flow of branch pipe acts as turbulent jet in finite space and interaction between the jet and main flow can create various eddies and develops high velocity fluctuation area near the main pipe wall as well as temperature fluctuation. Three regions are more affected by maximum velocity fluctuation in T-junction area near the main pipe wall; the region close to the jet surface (fluctuation mostly is caused by Kelvin-Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex) and re-attached area (fluctuation mostly is caused by moving the jet body with pressure gradient). Finally, the re-attached area is selected as region with strongest possibility to high cycle thermal fatigue with effective velocity fluctuation on the main pipe wall above the branch nozzle as well as temperature fluctuation.
CFD Study of Thrombus Formation on Shear Blood Flows for Developing Prediction Method of Thrombus
Authors: Tamagawa Masaaki
Published: March 2009

This paper describes development of the prediction method of thrombus formation by Computational Fluid Dynamics (CFD) on pipe orifice shear flows. These shear flows are typical models of the flow in the rotary blood pump. In this investigation, the thrombus formation in blood plasma flow is visualized, and modified lattice Boltzmann method are used to predict the backward forwarding step flow, that is simple model of the orifice flow.
A Research Project on Application of Air Bubble Injection to a Full Scale Ship for Drag Reduction
Authors: Kawashima Hideki , Kodama Yoshiaki , Hinatsu Munehiko , Hori Toshifumi , Makino Masahiko , Ohnawa Masashi , Takeshi Haruya , Sakoda Motoyuki , Kawashima Hisanobu , Matsuno Fumiko
Published: March 2009

This paper is a progress report of a research project toward practical use of air bubble injection as a drag reduction device for ships. Air bubbles injected into the turbulent boundary layer in water flow are well known to have significant skin friction reduction effect. The current research project will last for three years, starting in April 2005. The project aims at obtaining 10% net energy-saving by air bubble injection, taking into account the work needed for injecting air bubbles. A full scale experiment is scheduled in September 2007. The photo and principal particular of the ship used for the full scale experiment are shown in Figure 1 and Table 1. The ship has a wide and flat bottom. Therefore, once air bubbles are injected at the bottom near the bow, they are expected to cover the entire bottom surface efficiently. The air bubbles must be injected against the hydrostatic pressure at the point of injection. Estimation of the rate of drag reduction per unit amount of injected air at full scale is extremely difficult if it is based on small model-scale experiments, because the scale ratio of air bubbles to boundary layer length scales is very different between model and full scale experiments. Therefore we carried out experiments using a flat plate (L = 50m, B = 1m) in the 400m towing tank of the institute. The plate was towed at 6.2m/s (12kt), the cruising speed of the ship for a full scale experiment. Air bubbles were injected at 3m from the bow. Both the total drag of the flat plate and local skin friction were measured. Recently we attached end plates almost along the entire length, in order to prevent air bubbles from getting lost from the sides, and obtained significant improvement in drag reduction. Injected air bubbles are expected to go into the propeller operating at the stern and the propeller performance may deteriorate. Therefore we carried out tests of a model propeller working in bubbly flow. So far we found that the degradation of the propeller performance due to bubbles is small and tolerable. The project is carried out in collaboration with Osaka Univ., Hokkaido Univ., Tokyo Univ., Mitsui Engineering & Shipbuilding CO., LTD. and Azuma Shipping CO., LTD.. The project is funded by NEDO (New Energy and Industrial Technology Development Organization), Japan.
Data Analysis Methods for Stereo PIV of a High Aspect Ratio Flexible Cylinder
Authors: Furey D. , Atsavapranee P. , Cipolla K.
Published: March 2009

Stereo Particle Image velocimetry data was collected over high aspect ratio flexible cylinders (L/a = 1.5 to 3 × 105) to evaluate the axial development of the turbulent boundary layer where the boundary layer thickness becomes significantly larger than the cylinder diameter (δ/a>>1). The flexible cylinders are approximately neutrally buoyant and have an initial length of 152 m and radii of 0.45 mm and 1.25 mm. The cylinders were towed at speeds ranging from 3.8 to 15.4 m/sec in the David Taylor Model Basin. The analysis of the SPIV data required a several step procedure to evaluate the cylinder boundary flow. First, the characterization of the flow field from the towing strut is required. This evaluation provides the residual mean velocities and turbulence levels caused by the towing hardware at each speed and axial location. These values, called tare values, are necessary for comparing to the cylinder flow results. Second, the cylinder flow fields are averaged together and the averaged tare fields are subtracted out to remove strut-induced ambient flow effects. Prior to averaging, the cylinder flow fields are shifted to collocate the cylinder within the field. Since the boundary layer develops slowly, all planes of data occurring within each 10 meter increment of the cylinder length are averaged together to produce the mean boundary layer flow. Corresponding fields from multiple runs executed using the same experimental parameters are also averaged. This flow is analyzed to evaluate the level of axisymmetry in the data and determine if small changes in cylinder angle affect the mean flow development. With axisymmetry verified, the boundary flow is further averaged azimuthally around the cylinder to produce mean boundary layer profiles. Finally, the fluctuating velocity levels are evaluated for the flow with the cylinder and compared to the fluctuating velocity levels in the tare data. This paper will first discuss the data analysis techniques for the tare data and the averaging methods implemented. Second, the data analysis considerations will be presented for the cylinder data and the averaging and cylinder tracking techniques. These results are used to extract relevant boundary layer parameters including δ, δ* and θ. Combining these results with wall shear and momentum thickness values extracted from averaged cylinder drag data, the boundary layer can be well characterized.
A Comparison of Cavitation Inception Index Measurements to the Spatial Pressure Distribution Within a 2D Cavity Shear Flow
Authors: Liu Xiaofeng , Katz Joseph
Published: March 2009

Direct cavitation inception index measurements and observation on occurrence of cavitation are compared to results of novel spatial pressure distribution measurements in a 2D cavity shear flow. This non-intrusive technique utilizes four-exposure PIV to measure the distribution of material acceleration, and integrating it by means of omni-directional virtual boundary integration algorithm to obtain the pressure distribution (Liu and Katz, 2006). Consequently, it provides the instantaneous spatial distributions of velocity, material acceleration and pressure over a sample area along with their statistics. The present Reynolds numbers based on the cavity length vary from 1.7×105 to 3.4×105. High-speed imaging of cavitation inception, recorded at 30,000 fps, indicates that for this 2D cavity flow, the onset of cavitation always occurs on the top of the cavity trailing edge, regardless of the free stream speed. With decreasing pressure cavitation intermittently expand to the region located just in front of the cavity. The time-averaged spatial pressure distribution has a minimum just above the trailing edge due to the interaction of the impinging shear layer with the trailing wall. Around the cavity trailing edge, the mean flow first decelerates due to the impingement, but then accelerates right above the trailing edge, creating a local pressure minimum there. RMS values and PDFs of pressure fluctuations show that the highest fluctuations occur around the cavity trailing edge, and that the pressure peaks are consistent with the measured cavitation inception indices. There is also agreement between pressure statistics and conditions of appearance of cavitation in front of the trailing edge. The paper also provides the first directly measured experimental data on pressure-velocity correlation and pressure diffusion terms that appear in the evolution equation for turbulent kinetic energy. Results compared to other terms that act as sources and sinks in the turbulent kinetic energy balance. It is evident that near the trailing edge of the cavity, the contribution of pressure diffusion is comparable to that of turbulent kinetic energy production rate, and is much larger than the turbulent diffusion rate. Trends and spatial distribution of pressure diffusion also differs from those of turbulence diffusion.
Turbulence-Aberrated Laser Wavefront Profiling With Shack-Hartmann Microlenses
Authors: Freeman Aaron P. , Catrakis Haris J.
Published: March 2009

This study focuses on experimental profiling of turbulence-aberrated laser wavefronts using a Shack-Hartmann (S-H) microlens array as a means of investigating the aero-optical effects that large-scale turbulence properties have on propagated laser wavefronts. Imaging of the phase and intensity of laser sheets propagated through separated turbulent compressible shear layers, which cause the laser wavefront to become aberrated, is performed under the following flow conditions; Re ∼ 6×106 based on visual thickness and M∞ ∼ 0.9. The data captured by the S-H sensor enables the direct determination of the laser optical wavefront profile. The optical wavefront profile provides path-integrated information regarding the refractive turbulence field and interfaces. The optical wavefronts are compared with laser induced fluorescence images of the refractive fields and interfaces taken simultaneously which allows for verification of computational methods of analyzing the optical wavefront within the flow. The present work validates the use of laser wavefront profiling as a means for detecting information about the refractive turbulence properties.
Multiscale Aspects and Resolution Robustness of Turbulent Scalar Fields and Interfaces
Authors: Piatrovich Siarhei , Catrakis Haris J.
Published: March 2009

This study focuses on fundamental issues regarding multiscale and multiresolution geometrical properties of turbulent scalar fields and interfaces. The probability density function of the scalar field is examined in terms of geometrical properties of the turbulent interfaces using a high-resolution experimental database of fully-developed turbulent scalar fields in jets at a Reynolds number of Re = 20,000. The pdf is found to exhibit significant robustness to resolution scale. The multiscale properties of the volume of fluid regions enclosed by outer turbulent interfaces are also investigated. The enclosed interfacial volume appears to be significantly robust to the resolution scale as well. An explanation for this behavior is proposed in terms of the opposite effects of protrusions of the scalar interface compared to indentations, which provide positive and negative contributions to the volume respectively. This is in contrast to the interfacial surface area for which protrusions and indentations both have additive contributions.
Effect of Gravity on Axial Development of Gas-Liquid Two-Phase Flows
Authors: Uematsu Junichi , Abe Kazuya , Hazuku Tatsuya , Takamasa Tomoji , Hibiki Takashi
Published: March 2009

In pursuit of the development of the interfacial area transport equation, the axial development of void fraction profile, bubble number density, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured in normal and microgravity environments using stereo image-processing. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5.0, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00823–0.0303 m/s) and superficial liquid velocity (0.147–0.907 m/s). The effect of gravity on the radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the measured data and the visual observation.
A Study on the Spray Characteristics of a Liquid-Propellant Thruster Injector by PIV/PDA Optical Measurements
Authors: Kim Jeong Soo , Kim Jin Seok , Jung Hun , Park Jeong , Kim Sungcho , Jang Ki-Won
Published: March 2009

Spray characteristics of an injector employed in liquid-propellant thrusters are investigated by optical measurement techniques such as Particle Image Velocimetry (PIV) and Dual-mode Phase Doppler Anemometry (DPDA). The injector adopted in this experiment has 8 holes each of which has 30° cant angle from the center-axis with 16/1000 inches of hole diameter. Instantaneous plane images captured by PIV technique are examined in order to judge a pass-fail criterion of spray injection performance according to the specific pressures supplied. DPDA through which two-dimensional velocity components can be acquired is also applied in order to measure the velocity and size of spray droplets which were not obtainable from the PIV measurement. The non-dimensional parameters (e.g., Reynolds, Weber, and Ohnesorge numbers) based on the velocity data measured by DPDA are used to characterize the spray behavior in terms of the atomization and turbulence nature. Objectives of this experiment are to establish a non-intrusive evaluation technique for the injector performance and to utilize the clear understanding of spray characteristics for the design of brand-new thrust chamber as well.
An Improved High-Resolution Discretization Scheme for Volume-of-Fluid CFD Simulations
Authors: Walters D. Keith , Wolgemuth Nicole M.
Published: March 2009

A new high-resolution spatial discretization scheme for use with the interface capturing volume-of-fluid (VOF) method is presented and applied to several test cases. The new scheme is shown to preserve the volume fraction discontinuity within a single computational control volume (CV), without the need to explicitly reconstruct the interface within CVs near the interface. The method is based on maximization of the volume fraction gradient in the region of the interface, while stability is preserved by maintaining net upwind biasing of the face flux prescription in each CV. In addition, the scheme employs face limiting to satisfy physical boundedness criteria at finite-volume control surfaces (faces) and prevent variable overshoot. The method has been developed for use with unstructured, anisotropic, and/or inhomogeneous meshes that are often used for simulation of geometrically complex flowfields. This paper presents the implementation of the new discretization scheme into a steady-state solver in order to isolate the spatial discretization from the time integration technique. The new scheme is validated for steady-state two-phase flow using several demonstration test cases, and is shown to preserve the phase interface almost exactly, with essentially zero dissipative or dispersive error in the volume fraction solution. Results are compared to existing 2nd order and high-resolution interface capturing (HRIC) schemes, and shown to be superior in all cases.
Dynamic Fluid Saturation Method for Hydrocarbons Thermodynamics’ Properties Determination
Authors: Saab Joseph , Naccoul Ramy Abou , Stephan Juliette , Ouaini Rosette , Jose Jacques , Ouaini Naim
Published: March 2009

Low solubility compounds suffer from lack of data, leading to an impoverishment in thermodynamic parameters such as Gibbs free energy (ΔG), enthalpy of dissolution (ΔH), entropy (ΔS), infinite dilution coefficient (γ∞) and isobaric heat capacity (Cp) of utmost practical importance for industrial optimization processes. Dynamic fluid method is a novel technique for low solubility (expressed as molar fraction χ) determination based on the saturation of a specific heated fluid passing through a saturation cell. The heated components are kept inside a chromatographic oven maintained at a constant temperature to within ± 0.05°C by means of a PID temperature controller. A regular stream of fluid, using a constant flow pump, passes through the saturation cell packed with an inert stationary phase (Gaz chrom R 60/80) pre-coated with the organic compound. The solute transported by the fluid is subsequently trapped in a specific extraction column (inverse phase). The organic compound is removed by back flushing using the appropriate solvent in order to dissolve and carry out the totality. A low flow of fluid through the generator column is to be set to avoid safely the formation of colloidal dispersion, to increase the contact time and to keep small pressure drops across the generator/extractor column. The gas chromatography coupled to mass spectrometer detector is used in order to quantify the solute. The validation of this apparatus was achieved by comparison of our values with the ones extracted from previous papers using the static method to determine aqueous solubility of the ethylbenzene, and a precision of our solubility measurements was established to be better than 0.2%. In continuous, aqueous solubility and thermodynamics properties of perfluorocarbons compounds were determined in the range of temperature from 273 K to 333 K. Considering the contribution of chromatographic, calibration and other operational errors, the combined measurement uncertainty (standard deviation) was established to be less than 3%.
Drag and Mass Transfer of Bubble Swarms in Power-Law Liquids at Moderate Reynolds and Peclet Numbers
Authors: Kishore N. , Chhabra R. P. , Eswaran V.
Published: March 2009

The motion and mass transfer of swarms of mono-size non-circulating spherical bubbles (without any surface active material) in power-law liquids have been numerically investigated at moderate Reynolds and Peclet numbers. A simple sphere-in-a-sphere cell model has been used to account for hydrodynamic interactions between neighbouring bubbles. A wide range of values of gas hold-up has been considered so as to evaluate the detailed drag and mass transfer characteristics of swarms of bubbles to almost single bubble rising in power-law liquids. Extensive numerical results have been obtained to elucidate the effects of the Reynolds number (Re), power-law index (n) and gas hold-up (φ) on the drag coefficients and Sherwood numbers over the ranges of conditions: 0.6 ≤ φ ≤ 10−6, 1 ≤ Re ≤ 200, 1 ≤ Sc ≤ 1000 and 0.6 ≤ n ≤ 1.6. The total drag coefficient (CD) decreases with the decreasing values of n, whereas, the average Sherwood number (Shavg) decreases with increasing values of n. Based on the present numerical results simple predictive correlations have been proposed for CD and Shavg which can be used to estimate the free rising velocity and the rate of mass transfer in a gas-liquid system in a new gas-liquid application.
An Overset Chimera Unstructured Grid Method and Its Applications
Authors: Zhao Xiang , Zhang Sijun
Published: March 2009

In this paper, an overset Chimera method is extended to unstructured mesh, the unstructured grid solver enhanced by the overset Chimera method is employed to various specific applications, in which time dependent fluid flows involving multiple moving bodies needs to be solved. The present method possesses not only the novel feature of Chimera method but also the advantage of unstructured grid approach. Its robustness and efficiency are illustrated in this paper through typical applications.
Study on the Automated CFD Analysis Tools for Conceptual Design of Space Transportation Vehicles
Authors: Fujimoto Keiichiro , Fujii Kozo
Published: March 2009

In order to improve turnaround time and usability of the aerodynamic analysis tool such as for the conceptual design of space launch vehicles, an automated high fidelity numerical aerodynamic analysis method is developed. This method has capability of fully automated and quick execution from geometry modeling through flow computation for high Reynolds number viscous flow over complicated geometry. The present method is based on the locally-body-fitted Cartesian grid method, which is applicable for the viscous flow computation over the complicated geometry and is easy-to-use requiring less expertise. Since this grid generation method has not been established due to the lack of robustness for feature preserving technique, robust feature preserving technique is developed in this study. In addition, the present method is validated and its prediction capability is confirmed through the application to the typical test problems including transonic airfoil flows, supersonic hemisphere flows, and subsonic/supersonic separated flow over the Apollo capsule. Finally, the proposed aerodynamic analysis method is applied to an aerodynamic analysis of aerodynamic fin effect on the single-stage-to-orbit (SSTO) rocket vehicle.
Resist Stripping and Surface Cleaning Technique Using High Speed Steam-Droplet Mixture
Authors: Sanada T. , Shirota M. , Watanabe M. , Morita Y. , Yamase M.
Published: March 2009

A novel resist stripping and surface cleaning technique is proposed. We have improved wet vapor resist stripping technique (Ojima & Ohmi) using high-speed steam and purified water droplets mixture. Relatively low pressure steam (0.1MPa∼0.2MPa) is mixed with purified water in front of the nozzle, and sprayed to Si wafer with resist. Using this new technique, we are able to strip resist without chemicals very quickly and also to clean a wafer surface, i.e., to eliminate some particles. This technique has an advantage not only in reducing some processes of semiconductor manufacturing but also in maintaining chemical-free environment. Both droplet velocity and diameter distributions were measured by Phase Doppler Anemometer (PDA). Resist stripping was observed with a high-speed video camera and the fringes of the removed resist region were observed with a digital microscope. Mechanism of this resist stripping process is discussed.
Optimization of Multi Cylindrical Filters for Industrial Gas Processing Plants
Authors: Buzanowski Mac , Fadda Dani
Published: March 2009

Gas filters utilize multi cylindrical filter tubes to capture undesirable solids and remove them from a gas stream. An optimization effort described in this paper starts with commonly used multi cylindrical filters and aims at significantly decreasing the gas pressure drop across the gas filter resulting in possible reduction in the diameter of the vessel while maintaining acceptable pressure loss. Computational fluid dynamics (CFD) modeling is used to determine the effects of filter tube diameter and multi filter tube packing on the overall pressure drop across the vessel.
A Lagrangian Vortex Method for Two-Phase Particulate Flow Simulation
Authors: Gharakhani A.
Published: March 2009

The Lagrangian vortex method developed by Chen and Marshall [1] for two-way coupled two-phase flow simulation of (cloud of) solid particles is revisited in this paper. The algorithm attempts to merge the best attributes of the Lagrangian and two-fluid continuum models into one by applying the Lagrangian conservation of momentum simultaneously with the conservation of the concentration field along the trajectories of the particle clouds. In this paper, a consistent implementation is proposed, which is considerably less complicated and computationally more stable than the original formulation. In particular, it is shown that when a smooth particle representation of the concentration field is used, the Lagrangian conservation of particle momentum automatically satisfies conservation of the concentration field. This implies that the evaluation of the concentration field becomes a post-processing exercise as is common with the traditional Lagrangian (solid) particle method, although the new method yields much smoother concentration fields. In this paper the formulation for the modified approach, as well as results from basic benchmark tests are presented.
Numerical Analysis of Fluid-Structure and Fluid-Rigid Body Interactions Using a Particle Method
Authors: Koshizuka S. , Shibata K. , Tanaka M. , Suzuki Y.
Published: March 2009

An algorithm is presented for fluid-structure and fluid-rigid body interactions using a particle method. The algorithm is based on weak coupling, where fluid and solid analyses are explicitly connected in each time step. Fluid dynamics is solved by the Moving Particle Semi-implicit (MPS) method proposed by Koshizuka and Oka in 1996. Elastic solid dynamics is solved by the MPS method proposed by Song et al. in 2000. Rigid body motion is calculated by the particle method proposed by Tanaka et al. in 2007. The external force from the fluid to the rigid bodies is calculated by either volume integral or surface integral. When the volume integral is employed, both fluid and rigid bodies are calculated as fluid at first in each time step and then the rigid body dynamics is solved and the shapes are reconstructed. For fluid-elastic solid coupling, surface integral is necessary. Calculation examples using the present algorithms are shown.
Numerical Detection of a New Instability Mode of a Vortex Ring
Authors: Hattori Yuji , Fukumoto Yasuhide
Published: March 2009

The instability of a vortex ring is studied by direct numerical simulation of the Navier-Stokes equations. First we consider a vortex ring in a periodic cylindrical domain. The Widnall instability of bending waves is observed clearly. Next we consider a vortex ring confined in a torus. A novel method for solving the Navier-Stokes equations with high accuracy in a torus is developed and used in the simulation. The curvature instability, which is found by the authors recently, is captured for the first time. The growth rate of unstable modes agrees well with the value obtained by linear stability analysis. The structure of destabilized vortex ring is investigated in detail.
Development of a Large-Flow-Rate Mist Generator: Prediction of Hydraulic Performance
Authors: Sadatomi M. , Matsuyama F. , Kawahara A. , Fukamachi K.
Published: March 2009

Sadatomi (2003) invented a micro-bubble generator with a spherical body in a flowing water tube. In the generator, when pressurized water is supplied to the tube, air is automatically sucked through many small holes drilled on the periphery of the tube behind the body, and is broken into a number of micro-bubbles by a high-shear flow of water around the body. In the present study, in order to develop a large-flow-rate mist generator, pressurized air is supplied to the same generator and water is automatically sucked. Experiments were conducted to study the effects of parameters, such as the diameter ratio of the spherical body to the tube, on the hydraulic performance, and the data on the mist flow rate, the pressure at the generator inlet and the distribution of mist diameters were obtained by changing the air supply rate. In the analyses, an analytical model is proposed to predict the mist flow rate and the pressure at the generator inlet at a given air supply rate. In order to validate the model, a comparison is made between calculation and experiment. Results of the experiments and the comparison together with the model are presented in this paper.
Manipulation of the Flow Around a Circular Cylinder by Utilizing the Flow Receptivity
Authors: Kozato Yasuaki , Kikuchi Satoshi , Imao Shigeki
Published: March 2009

An attempt to control the flow around a circular cylinder by utilizing the receptivity to the external acoustic disturbance was carried out and its mechanism was also studied. The velocity fields around the cylinder vicinity are carefully investigated with an X-type hot-wire probe. When the disturbance of a higher frequency related to the separated shear layer instability is added, the development of turbulence and the spreading of the shear layer are restrained. And, the amplification of the fluctuating velocity component of the Karman vortex shedding is delayed and its degree is reduced. Furthermore, the process of the gradual scale modification of the shear layer instability that appears prior to the transition of the flow is suppressed.
LES Analysis of Flows Around a Forced-Oscillating Circular Cylinder
Authors: Sato Norikazu , Kawakami Mitsuyoshi , Inagaki Masahide
Published: March 2009

Large eddy simulation (LES) of flows around a forcedoscillating circular cylinder is carried out using the Arbitrary Lagrangian-Eulerian (ALE) method and a central difference scheme for the convection terms, which is a newly proposed discretization scheme that improves the conservation properties of the mass, momentum, and especially kinetic energy. The results are compared with the measurements that are also carried out by authors, in terms of lock-in phenomenon. It is shown that the numerically predicted pressure and velocity distributions are in good agreement with the experimental data, both in the lower and the upper lock-in region, and the phase difference between the cylinder displacement and the vortex shedding is consistent with previous findings. In addition, it is clarified that the frequency range of the lock-in in LES is almost the same in width as that of the experiment, while it becomes wider in the comparative analysis, in which the QUICK scheme is employed for the convection terms. Such discrepancies between two calculations are prominent, especially in the stationary and the lower frequency region.
A Very Simple Immersed Boundary Method Applied to Three-Dimensional Incompressible Navier-Stokes Solvers Using Staggered Grid
Authors: Yamamoto Satoru , Mizutani Koichiro
Published: March 2009

A very simple computational algorithm for solving flows over complex geometries is presented. This algorithm is based on a kind of the Immersed Boundary (IB) Methods. The complex 3D geometries are generated by the 3DCG software as a surface mesh of triangle polygons. A 3D Cartesian grid is used for the flow field. Only the points stuck with grid lines on triangle polygons are detected and flow velocities are modified using the points with the IB method. In this paper, this approach is applied to an incompressible Navier-Stokes solver based on the Simplified Marker and Cell (SMAC) method. Some practical flow problems assuming low Reynolds number are calculated and the results are compared with the experimental and the numerical results.