bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Turbulent Boundary Layer Over Silicon Gel Surface and Behavior of Surface Displacement
Authors: Fujimatsu Nobuyoshi , Misu Isao , Ishimaru Kenta
Published: March 2009

This paper describes a study on interaction between compliant coatings and turbulent boundary layer flows. The use of compliant coatings has been known as the drag reduction means of the skin-friction and was studied by many researchers for 50 years. However the mechanism of drag reduction is not clarified. In this study, experimental study was conducted using compliant walls made of silicone gel to investigate the influence of compliant coating on the flow field. Boundary layer characteristics and displacement of the walls were simultaneously measured using hot-wire anemometer and a laser displacement sensor. The experimental results showed the suppression of the turbulent intensity turbulent skin-friction drag reduction over the compliant wall. Characteristics of the turbulent energy cascade process over the solid and compliant walls are investigated using the Wavelet transform and the FFT. The compliant coatings suppress the turbulent energy production and enhance the turbulent energy dissipation compared to those of the solid wall. The cross correlation between the displacement of the compliant wall and the velocity fluctuation in the turbulent boundary layer are investigated in detail. The phase difference angle of the motion of the compliant wall to the velocity fluctuation is about 60 degrees. This wall motion has the roll to suppress the turbulent vortex motion near the wall. The drag reduction mechanism on the compliant coating can be explained as philosophy based on the V-control algorithm.
Least Square Data Reconstruction Approach for Unstructured Grid
Authors: Zhang Sijun , Jain Kunal
Published: March 2009

This paper presents least square higher order data reconstruction schemes for unstructured grid to enhance the accuracy and robustness of CFD simulations for practical problems. The schemes consist of five novel approaches to more accurately reconstruct 1) the cell-centered data to cell faces, 2) gradient calculation, 3) skew terms for diffusion, 4) skew terms for conjugate wall, and 5) skewness correction for pressure-velocity-density coupling equation. These schemes have demonstrated effectiveness on some critical cases and many problems, and strong potential to improve the accuracy and robustness of CFD computations.
Flow Development in a Circular Duct With a Highly Distorted Inlet Condition
Authors: Badam Srinivas , Cui Jie , Idem Stephen
Published: March 2009

The development of air flow downstream of a stationary fan located in a circular duct was investigated. The objective of the research was to study the evolution of the velocity profiles and pressure gradients at various axial locations. The velocity profiles were measured at three different Reynolds numbers using a five-hole directional probe. Because the stationary fan caused the inlet velocity profile to be highly distorted, it was determined experimentally that the development length exceeded 20 duct diameters. Since this was greater than the length of the apparatus, a corresponding numerical model of the flow was generated using the commercial CFD software Fluent-6.1/6.2. The numerical model was validated against the experimental results. The hydrodynamic development length was therein determined numerically.
Numerical Estimation of Exhaust Gas Emission From Tunnel Portal With Forced Extraction System
Authors: Yamada Kentaro , Iida Akiyoshi , Mizuno Akisato
Published: March 2009

In recent years, exhaust gas emission out of tunnel portals has been a problem. In order to maintain the environment around the tunnel portal, a concentrated exhaustion system is installed in some tunnels. In the area between the suction port and the portal, the air flows in the opposite direction to the traffic, so that the pollutant is sucked toward the exhaustion port. In order to grasp the detailed phenomena, the authors investigated quantitatively the extent of the pollutant, which is brought out of the tunnel portal, in terms of a three-dimensional numerical analysis. This simulation system includes a sliding mesh algorithm in order to express the movement of vehicles. A typical result of the suction velocity of 1.0 m/s showed that almost no emission out of the tunnel is observed in small car traffic.
The Effects of the Wall-Layer Models on the Outer Turbulence Structures in Large Eddy Simulation of Pipe Flows
Authors: Tsubokura Makoto , Oto Yasuo , Etoh Jun , Piao Binghu , Kuroda Shigeaki
Published: March 2009

Reproduction of the outer turbulence in Large Eddy Simulation (LES), when the wall-layer model is adopted in the inner layer, is investigated to validate the hybrid RANS/LES as an approximate near-wall treatment. Special emphasis is on the possibility of Detached Eddy Simulation (DES) for the reproduction of outer large (∼ R) and very large (∼ 10R) streaky structures typically observed in the pipe turbulence. LES and DES of fully developed turbulent pipe flows at the friction Reynolds number up to 5000 are conducted using a very long analysis region to capture entire outer scales. It is found that the outer scales are properly captured in DES independent on the unphysical super-streaks in the RANS region near the wall, as long as sufficient height for the DES buffer layer is maintained. Our results shed light on the origin of the outer structures, which are rather autonomous similar to the inner sublayer streaks, and these two structures with different scaling exists in the isolated manner.
Numerical Study of Turbulent Flow in a Tangentially Injected Swirl Generator
Authors: Mogili Sandeep , Cui Jie
Published: March 2009

The swirl effects in inert and reacting flow systems have been studied for many years. Some processes have appreciated the presence of swirl while some have entitled to curtail the swirl. The swirl intensity is an important parameter in characterizing flows with swirl. In this study, the turbulent flow in a tangentially injected swirl generator was analyzed using commercial CFD software Fluent. The Reynolds numbers considered were 12,500, 15,300, and 30,600 for a fixed ratio of tangential to total momentum flux of 7.84. At Reynolds number 12,500, several cases with various injector configuration and momentum flux ratio were also studied. The numerical results were validated with available experimental data. The results showed that the flow in the generator can be classified into two regions, core and annulus. Reversed flow region was observed in all these cases. The swirl intensity was found to decay exponentially along the axial lengths. The simulations also showed that the swirl intensity was significantly affected by the momentum flux ratio and the Reynolds number.
3-D Vortex Simulation of Accelerating Flow Over A Simplified Opening Bileaflet Valve
Authors: Gharakhani A.
Published: March 2009

A fast, parallel Lagrangian vortex method, Ω-Flow, is developed for the grid-free Large Eddy Simulation (LES) of unsteady incompressible flow about 3-D moving objects. The latter is used to simulate external flow over a simplified model of a St. Jude Medical bileaflet mechanical heart valve. In this model, the freestream is accelerated from zero to peak Reynolds number 5,000 using a physiologically realistic velocity waveform; while, simultaneously, the valve leaflets are rotated with a parabolic angular velocity waveform from “closed” to “open” positions. This paper briefs the numerical methodology, as well as partial results from the convergence study.
An Approach for Inclusion of a Non-Local Transition Model in a Parallel Unstructured CFD Code
Authors: Kozˇulovic´ Dragan , Lapworth B. L.
Published: March 2009

The implementation of an integral transition model in a parallel unstructured CFD code is described. In particular, an algorithm for gathering the non-local boundary layer values (momentum thickness, shape factor, etc.) from parallely distributed computational domains is presented. Transition modelling results are presented for a flat plate and for a low pressure turbine, covering a large range of Reynolds numbers, Mach numbers, turbulence intensities and incidence angles. The transitional predictions are in much better agreement with the measurements than fully turbulent simulations. Furthermore, the computational overhead of transitional simulations is only 7% for one multigrid cycle.
Simulation for Forces on Levitated Droplet in Ultrasonic Standing Wave
Authors: Aoki Kazuyoshi , Hyuga Daisuke , Abe Yutaka
Published: March 2009

Under the micro-gravity environment, holding technology of liquid is important to manufacture new materials and noncontact material property measurement methods. There are previous studies about droplet levitation by the ultrasonic standing wave for the holding technology. However it is still unknown experimentally and analytically how the ultrasonic standing wave acts on the levitated droplet. In the present study, the technology to handle the material in space by the ultrasonic wave is developed and the simulation technique to evaluate the ultrasonic standing wave field and the movement of the droplet in the ultrasonic standing wave. At first, the characteristics of droplets holding by the ultrasonic standing wave under normal gravity environment and micro-gravity environment are investigated experimentally. Secondly, pressure field by ultrasonic standing wave is measured with probe microphone. The measurement shows that 2-dimensional pressure distribution is arisen between the horn and the reflector, and positions where droplets are held are near nodes of the ultrasonic standing wave. Thirdly, numerical simulation considered for compressibility of gas is conducted to clarity the characteristics of ultrasonic standing wave. The 2-dimensinal pressure distribution obtained by this simulation agrees with the measurement result by probe microphone quantitatively. Finally, droplet movement is solved using results of pressure field simulation. It is shown that 2-dimensinal pressure distribution causes horizontal holding force.
Heat Transfer and Air Diffusion Phenomena in a Bed of Polymer Powder Using Apparent Heat Capacity Method: Application to the Rotational Molding Process
Authors: Boutaous M. , Pe´rot E. , Maazouz A. , Bourgin P. , Chantrenne P.
Published: March 2009

The process of rotational moulding consists in manufacturing plastic parts by heating a polymer powder in a biaxial rotating mould. In order to optimise the production cycle of this process, a complete simulation model has to be used. This model should describe the phenomena of heat and mass transfer in a moving granular media with phase change, coalescence, sintering, air evacuation and crystallization during the cooling stage. This paper focus on the study of heat and mass transfer in a quiescent polymer powder during the heating stage. An experimental device has been built. It consists in an open plane static mold on which an initial thickness, e, of a polymer powder is deposited. This powder is then heated until it melts. An inverse heat conduction method is used to determine the heat flux and temperature at the interface between the mold and the powder. This interfacial heat flux is taken as a boundary condition in a numerical heat transfer model witch takes into account the heat transfer in granular media with phase change, coalescence, sintering, air bubbles evacuation and rheological behaviour of the polymer. For the numerical simulation of the heat transfer, the apparent specific heat method is used. This approach allows to solve the same energy equation for all the material phases, so one do not have to calculate the melting front evolution. This fine modelling, close to the real physical phenomena makes it possible to estimate the temperature profile and the evolution of the polymer powder characteristics (phase change, air diffusion, viscosity, evolution of the thermophysical properties of the equivalent homogeneous medium, thickness reduction, air volume fraction...). Several results are then presented, and the influence of different parameters, like the thermal contact resistance, the process initial conditions and the polymer’s rheological characteristics are studied and commented. Indeed the predictions of the temperature rises in the polymer bed, agree well with the experimental measurements.
The Effects of the Synthetic Jet on the Mixing Promotion in Low Reynolds Number
Authors: Higashiura Masashi , Inose Koichi , Motosuke Masahiro , Honami Shinji
Published: March 2009

The present paper describes a synthetic jet interaction with the cross flow in low Reynolds number condition by flow visualization and the wall static pressure measurements. The primary focus of the current study is to examine the possibility on the interaction of the synthetic jet with the cross flow in low Reynolds number viscous dominant flow. The low bulk velocity of the cross flow is set in a small scale of the wind tunnel with a high aspect ratio. A wide range of Reynolds number based on the tunnel height and the bulk velocity is covered. The flow visualization at Reynolds number of 1,000 is conducted in X-Y and Y-Z planes to clarify the development of the interaction process in the downstream. Both the time averaged and phase averaged wall static pressure were obtained downstream of the jet injection. The synthetic jet has a diameter of 0.5 mm and a frequency of 100 to 400 Hz. The penetration of the jet in the cross flow depends on the jet velocity ratio, and the deepest penetration occurs at the phase of π/2 at the highest jet velocity ratio. The counter rotating longitudinal vortex pair is generated even in low Reynolds number and can be observed at 100d downstream from the injection. The vortex pair shows the up-wash motion at the center of the jet core and the down-wash motion at the outsides of the jet. For the synthetic jet in cross flow, the fluctuated wall static pressure is increased, and the wall static pressure has similar frequency to the synthetic jet.
Measurement of High-Speed and High-Number-Density Droplets by Micro-Probe L2F With Mega-Hertz Data Acquisition
Authors: Sakaguchi Daisaku , Ueki Hironobu , Ishida Masahiro , Amida Oluwole
Published: March 2009

A laser 2-focus velocimeter (L2F) has been applied for the measurements of velocity and size of droplets in the core region of diesel spray. The L2F has a micro-scale probe which consists of two foci. The focal diameter is about 2 μm, and the distance between two foci is 20 μm. The feature of this L2F is that the focus is reduced to near the diffraction limit. Investigated was the fuel spray injected intermittently into the atmosphere from an injector nozzle with the orifice diameter of 0.113 mm. The injection pressure was set at 40 MPa by using a common rail system. Measurement positions were located at 10 to 30 mm apart from the orifice exit along the spray axis. Valid data were extracted by a conditional sampling method based on the fact that a droplet passes through both upstream and downstream foci. Measurement result shows that the velocity and size of droplets decrease with the distance along the spray axis. It is clearly shown that the distance between droplets in isotropically dispersed condition decreases with the distance along the spray axis.
Experimental Study of Dynamic Characteristics of a Centrifugal Blood Pump With a Conical Spiral Groove Bearing for a Ventricular Assist Device
Authors: Nakamura Youichi , Tsukamoto Hiroshi , Miyazaki Koji , Qian Yi
Published: March 2009

Ventricular assist device (VAD) has been effective for cardiac patient. The VAD is set downstream of the heart, the pulsation of which effects the blood pump of the VAD. Therefore, the dynamic characteristics of the blood pump are important. In this study, we investigated the dynamic characteristics and rotor whirling motion of a centrifugal blood pump with a Conical Spiral Groove Bearing (CSGB). The flow through the pump was excited from 0.25 to 3 Hz by the vibration exciter in the mock circulatory system, and the conditions for stability of the blood pump were determined based on the dynamic characteristics tests.
Symmetric Model of Capillary Collapse and Rupture (Keynote)
Authors: Lundgren T. S. , Joseph D. D.
Published: March 2009

The breakup of a liquid capillary filament is analyzed as a viscous potential flow near a stagnation point on the centerline of the filament towards which the surface collapses under the action of surface tension forces. The analysis given her is restricted to cases in which the neckdown is symmetric around the stagnation point. We find that the neck is of parabolic shape and its radius collapses to zero in a finite time; the curvature at the throat tends to zero much faster than the radius, leading ultimately to a microthread of nearly uniform radius. During the collapse the tensile stress due to viscosity increases in value until at a certain finite radius, which is about 1.5 microns for water in air, the stress in the throat passes into tension, presumably inducing cavitation there.
Investigation of Luminous/Nonluminous Radiation in a Vortex Engine
Authors: Saidi M. H. , Kargar M. , Ghafourian A.
Published: March 2009

Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in combustion for scientists and combustion researchers. In this research some parts of the combustion chamber wall are insulated using Blanket as a high insulating material. The rate of radiative heat transfer to the chamber wall is calculated using temperature difference between inner and outer surface of chamber. In the experiments this parts are protected from direct contact with hot combustion media using quartz window. The luminous radiative transfer per volume of chamber and also volume of flame in a vortex engine are compared with that in a similar axial flow type engine. A detector sensitive to emission from C2* excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2* emission from flame.
Simulations to Determine Laminar Loss Coefficients in Arbitrary Planar Dividing Flow Geometries
Authors: Lemley Evan C. , Papavassiliou Dimitrios V. , Neeman Henry J.
Published: March 2009

The goal of this study is to determine laminar stagnation pressure loss coefficients for planar dividing flow. These losses are of clear interest in understanding flow in microfluidic devices, in porous media, or other complicated laminar pore networks. There is no published set of pressure loss coefficients for arbitrary bifurcation geometries that occur in these networks. Additionally, the small number of bifurcation geometries that have been studied are for turbulent flow often found in fluid supply and drain systems. The pressure loss coefficients determined in this study allow realistic simulation of existing laminar flow networks or the design of these networks. This study focuses on a single inlet duct with two outlet ducts, which were allowed to vary in diameter, flow fraction, and angle — all relative to the inlet duct. Laminar stagnation pressure loss coefficients have been determined by simulating incompressible flow through 600 different geometries. In all cases, the flow is laminar in the inlet and outlet ducts. Simulations of the dividing flow geometries were done using FLUENT and a custom written computer code, which automates the process of creating flow geometries, of creating FLUENT input files, and of parsing FLUENT output. The outputs, pressure and velocity distributions at the inlet and outlets, have been averaged and then used to calculate pressure loss coefficients for each of the geometries and flow fraction scenarios simulated. The results for loss coefficient for the geometries considered range from 0.15 to 49. The loss coefficient for any geometry increases significantly as the flow fraction increases and as the duct size of an outlet duct relative to the inlet duct decreases. Less significant variation of the loss coefficient has been observed as a function of the angles of the exit ducts.
Time-Accurate Measurement of Pressure From Particle Image Velocimetry Data (Keynote)
Authors: Charonko John J. , Vlachos Pavlos P.
Published: March 2009

This paper explores the challenges associated with the determination of pressure from DPIV-measured planar velocity fields for time-dependent incompressible flows. Several methods that have been previously explored in the literature are compared, including direct integration of the pressure gradients, and solution of different forms of the pressure Poisson equations. Their dependence on grid resolution, sampling rate, and velocity measurement error levels was quantified using artificial data of two ideal sample flow fields — a decaying vortex flow and pulsatile flow between two parallel plates. The need for special attention to mitigate the velocity error propagation in the pressure estimation is also addressed using a physics-preserving method based on Proper Orthogonal Decomposition. Finally, the methods developed are applied to sample Time Resolved DPIV experimental data corresponding to separated flow over an airfoil and pulsatile flow through an artery. The results demonstrate that there is no unique or optimum method for estimating the pressure field and the resulting error will depend highly on the type of the flow. Estimated errors can vary from less than 1% to over 100% with respect to the expected value. However, the analysis offers valuable insight that allows optimizing the choice of methods and parameters based on the flow under consideration.
Phase Correlation Processing for DPIV Measurements: Part II — Spectral Domain Analysis
Authors: Eckstein Adric C. , Charonko John J. , Vlachos Pavlos P.
Published: March 2009

A novel Digital Particle Image Velocimetry (DPIV) correlation method is introduced which estimates the displacement using the phase content within the Fourier based cross-correlation. The use of weighted least squares and robust least squares estimation is introduced in order to improve the linear phase estimation of this technique. Spectral filters are constructed using the energy content of PIV images to define weighting functions for the dominant singular vector regressions. This performance of this technique is measured using Monte Carlo simulations of DPIV images. The resulting error analysis demonstrates substantially reduced errors for higher particle-image diameters for images containing low amounts of noise. For high noise images, the reduction in bias and RMS errors is not as drastic due to limitations of extracting the phase information. However, this correlation technique is able to eliminate peak-locking errors, shown to be a substantial source of error in noisy images, by directly extracting the displacement information in the spectral domain.
On the Modelling of a Synthetic Jet as a Spherical Jet
Authors: Krishnan Gopi , Mohseni Kamran
Published: March 2009

The properties of a flow field of a synthetic jet are studied using hot wire anemometry. The experimental results are compared with an analytical model of a continuous jet derived in spherical coordinates. The radial velocity profiles at various radial distances from the synthetic jet orifice, when scaled appropriately collapse into a single self similar profile. The time averaged flow field can be modeled as an axially symmetric jet, with the replacement of empirical constants obtained from the measurement of the synthetic jet. It is shown that the synthetic jet has a higher spreading rate, and effective viscosity than that of an equivalent turbulent jet with constant mass flow rate. The analytical model in spherical coordinates is shown in this case, to better represent the experimental data than a model derived in cylindrical coordinates.
A Controls-Based Methodology for Generating Turbulence in Direct and Large-Eddy Simulations of Wall-Bounded Flows
Authors: Krishnan Vivek , Milano Michele , Squires Kyle D.
Published: March 2009

An integral control scheme is used to optimize a method for generating turbulent fluctuations for DNS and LES of wall-bounded flows. Similar to previous investigations, the method employs a series of control planes in which a body force is applied to the wall-normal momentum equation that amplifies and shapes velocity fluctuations seeded into the flow towards a target resolved shear-stress profile. The focus of the current work is on a methodology for specifying the controller gains and ensuring numerical stability without the introduction of criteria that override the control commands in order to prevent unphysical effects. The first method used to analyze the control process is based on identification of a linear model formed from the open-loop response of the shear stress to random inputs at the control planes. Optimal gains for the controller are specified based on the location of the poles of the linear model in the closed-loop configuration. The second method consists of measuring the response of the non-linear system to preset gain values and incrementally increasing the gains until the onset of numerical instabilities. The schemes have been tested using computations of turbulent channel flow at Reynolds numbers based on friction velocity and channel halfwidth of 400 and 5000. Simulation results obtained using both methods show that using the second approach the resolved shear stress reaches the target levels at the control planes, without ad hoc tuning of the control parameters. The predicted optimal gain values at the control planes are sensitive to the stirring force used to create fluctuations. In addition, the magnitude of the stirring force also affects rms values of the velocity fluctuations downstream of the control planes.
Pressure Drop in Slurry Pipe With Stationary Deposit
Authors: Matousˇek Va´clav
Published: March 2009

Majority of slurry pipelines operates at flow velocities high enough to maintain all transported solid particles in motion. Nevertheless, it happens sometimes that pipeline operations with stationary deposits of solids at the bottom of a pipe are found in practice (e.g. sand transportation through long pipelines connected with a dredge). Many different models are available for a prediction of the pressure drop in a slurry pipe without a deposit. Very little is known about flows with stationary deposits. The paper discusses pipe flows of sand-water slurries at velocities lower than the deposition-limit velocity. Results of laboratory tests of slurry flows with granular beds at the bottom of a slurry pipe are analyzed with an aim to establish a predictive model for the frictional pressure drop associated with this type of slurry flow. The pressure-drop model is based on a description of prevailing mechanisms that are identified to govern solids dispersion and solids friction in slurry flows at different conditions (e.g. different average concentrations of solids above the stationary bed, different dimensions of the discharge area above the bed etc.). The proposed model is composed of continuity, momentum, boundary-friction and particle-dispersion equations. The empirical stratification-ratio equation relates the effect of particle dispersion within the slurry flow with the flow friction at the top of the stationary deposit. This friction is recognized as a major contributor to the total pressure drop in the slurry flow through a pipe with a stationary deposit.
Development of Surface Skin Friction Measurement Technique Based on Compliant Coatings
Authors: Fujimatsu Nobuyoshi , Misu Isao
Published: March 2009

New method and means are proposed to measure the skin friction force on an aerodynamic surface based on elastic deformations of silicon rubber and gel coatings. One of characteristics is soft and easy to deform. Object is coated by elastic polymeric film with known shear modulus. Two images between wind-on and wind-off are taken using the CCD camera. The displacement of coating is calculated from the correlation of two images. There are two ways to calibrate the skin friction force to the displacement of coatings. These methods are tested and compared to quantitative skin friction force measurement. One is based on measuring the characteristics of the polymeric film using visco-elastic measurement system. This way is called as a priori calibration. The other way is accomplished from the relation between the skin friction force measured by the PHF embedded on the object and the displacement around there and is known as In-situ method. Characteristics of the coatings such as the displacement and the time response can be easily controlled by the compounding ratio of hardener. We conduct the theoretical analysis for the elastic polymer film and propose the material properties of the coatings required to measure the surface skin friction in the wide range of flow speed. The skin friction over the plate is measured using this technique in various Reynolds number. The traditional measurement using the hot wire anemometry is conducted to validate this technique. The time averaged measurements of this technique are in good agreement with the traditional results. However, the unsteady characteristics of surface skin friction are not captured by the lack of time resolution of the CCD camera.
LES for NO Prediction in a Propane-Air Turbulent Flame
Authors: Paul Sreebash C. , Paul Manosh C. , Jones William P.
Published: March 2009

Formation of nitric oxide (NO) in a model cylindrical combustor is investigated by applying Large Eddy Simulation (LES) technique. Gaseous propane (C3H8) is injected through a circular nozzle attached at the centre of the combustor inlet and preheated air with temperature of 773K is supplied through the annulus surrounding of the nozzle. The non-premixed combustion process is modelled via conserved scalar approach with laminar flamelet model, while in NO formation model, the extended Zeldovich (thermal) reaction mechanism is taken into account through a transport equation for NO mass fraction. In LES the governing equations are filtered using a spatial filtering approach to separate the flow field into large scale eddies and small scale eddies. The large scale eddies are resolved explicitly while the small scale eddies are modelled via Smagorinsky model.
On the Numerical Prediction of Interfacial Instabilities in Shear Flows (Keynote)
Authors: Nourgaliev Robert , Liou Meng-Sing , Theofanous Theo
Published: March 2009

We assess the state of the art in numerical prediction of interfacial instabilities due to shear in layered flows of viscous fluids. Basic ingredients of this assessment include linear stability analysis results for both miscible (diffuse) and immiscible (sharp) interfaces, the physics and resolution requirements of the critical layer, and convergence properties of the relevant numerical schemes. Behaviors of physically and numerically diffuse interfaces are contrasted and the case for a sharp interface treatment for reliable predictions of this class of flows is made.
Wind Tunnel Testing and Computational Fluid Dynamics Analysis of a Wing-in-Ground Effect Vehicle
Authors: Soh Boonseng , Low Andrew , Bil Cees , Bobbermien Brendon
Published: March 2009

The Wing-in-Ground Effect Concept Technology Demonstrator (WIGE CTD) project is a joint venture between Advanced Aerosystem Technologies Pty Ltd and RMIT University, aiming to design, validate and build a prototype recreational vehicle to fly two passengers over a distance of 500km at approximately 120km/h. The WIGE vehicle will fly very close to the surface, usually water, taking advantage of ground effect to transport passengers with a greater lift/drag ratio, and thus greater fuel-efficiency than conventional aircraft. Following preliminary design, an aerodynamic analysis of the vehicle was performed using wind tunnel testing and Computational Fluid Dynamics (CFD). This paper describes the methods used for wind tunnel testing and CFD modelling of the WIGE CTD design. Results obtained using the two approaches are compared with the aim of validating the CFD model and the techniques used in both wind tunnel and CFD modelling for use in future analyses. In addition to the aerodynamic analysis, a basic CFD prediction of the maximum hydrodynamic drag experienced during take off was attempted using a simple model of the WIGE vehicle hull. This result is required in order to ensure that the aquatic take off required by WIGE vehicles was possible for the design. Concurrently, the feasibility of using a general-purpose CFD solver like Fluent to analyse hull performance was also evaluated through this aspect of the investigation.
Adaptation of CFD to the Design of Centrifugal Pumps
Authors: Yedidiah Shmariahu
Published: March 2009

The similarity between flow patterns predicted with the aid of CFD and those observed in practice indicates, that CFD might be capable to assist the pump -engineer in coming up with improved designs. Unfortunately, in practice, the results are rather elusive. This paper discusses some of the causes of this state of affairs and presents suggestions, how to eliminate them. It demonstrates that the main cause of these disappointing results is the existing gap between science and engineering. The present explosion of information makes it very difficult for an expert in any given field of engineering to follow all the new developments in his (her) own specialized area. The less can an engineer be distracted by attempts to master an additional field of expertise. The results arrived at with the aid of CFD demonstrate, that it is a very powerful and versatile logical tool. However, versatile also means that it can be used in many different ways. Consequently, in order to arrive at satisfactory results, it has to be applied in a manner specifically suitable for handling the problem, which is being worked on. This means, that it requires an in-depth familiarity with all its aspects. Something, a CFD expert cannot afford to study. The only solution is teamwork. However, for teamwork to be successful, each participant has to know and to understand, what the others are doing. This paper demonstrates, that a relevant interpretation of the physical meaning of mathematical equations is capable to provide logical explanations to some of the even most enigmatic events. This leads to the conclusion, that such interpretations may also be capable to establish the so badly needed mutual understanding between the pump-expert, and the specialist in CFD. The above conclusions are supported by actual case histories from practice, and/or by results of tests. In addition to the above, this paper discusses a case history, which demonstrates that even in cases, in which CFD is capable to provide the required results, its use is not always the best choice. In practice, it is often much simpler, faster and considerably less expensive to arrive at the required results by means, which can be hardly regarded as associated with fluids dynamics. Finally, this paper also presents an example of a problem, which only CFD may be capable to solve.
Numerical Investigation of Gas-Solid Suspension Flow in 180° Curved Duct
Authors: Ibrahim K. A. , El-Kadi M. A. , Hamed Mofreh H. , El-Behery Samy M.
Published: March 2009

In this paper, a two-way coupling Eulerian-Lagrangian approach is presented for the simulation of gas-solid two-phase flow in 180° curved duct. In the present study, Reynolds averaged Navier-Stokes equations (RANS) and two turbulence models namely; standard k-ε model and RNG (Renormalization Group) based k-ε model are adopted. The effects of particle rotation and lift forces are included in the particle tracking model while the effect of inter-particle collisions is neglected. The present predictions are compared with published experimental data for single-phase flow and published particles trajectories. The comparisons show that the RNG based k-ε model predicts the flow behaviour better than the standard k-ε model. Furthermore, the particles trajectories are compared very well with published data. The effects of inlet gas velocity, bend geometry, loading ratio and solid properties on the flow behaviour are also discussed. The results show that the flow behaviour is greatly affected by the above parameters.
Applications of CFD Method to Gas Mixing Analysis in a Large-Scaled Tank
Authors: Lee Si Y. , Dimenna Richard A.
Published: March 2009

The computational fluid dynamics (CFD) modeling technique was applied to the estimation of maximum benzene concentration for the vapor space inside a large-scaled and high-level radioactive waste tank at Savannah River site (SRS). The objective of the work was to perform the calculations for the benzene mixing behavior in the vapor space of Tank 48 and its impact on the local concentration of benzene. The calculations were used to evaluate the degree to which purge air mixes with benzene evolving from the liquid surface and its ability to prevent an unacceptable concentration of benzene from forming. The analysis was focused on changing the tank operating conditions to establish internal recirculation and changing the benzene evolution rate from the liquid surface. The model used a three-dimensional momentum coupled with multi-species transport. The calculations included potential operating conditions for air inlet and exhaust flows, recirculation flow rate, and benzene evolution rate with prototypic tank geometry. The flow conditions are assumed to be fully turbulent since Reynolds numbers for typical operating conditions are in the range of 20,000 to 70,000 based on the inlet conditions of the air purge system. A standard two-equation turbulence model was used. The modeling results for the typical gas mixing problems available in the literature were compared and verified through comparisons with the test results. The benchmarking results showed that the predictions are in good agreement with the analytical solutions and literature data. Additional sensitivity calculations included a reduced benzene evolution rate, reduced air inlet and exhaust flow, and forced internal recirculation. The modeling results showed that the vapor space was fairly well mixed and that benzene concentrations were relatively low when forced recirculation and 72 cfm ventilation air through the tank boundary were imposed. For the same 72 cfm air inlet flow but without forced recirculation, the heavier benzene gas was stratified. The results demonstrated that benzene concentrations were relatively low for typical operating configurations and conditions. Detailed results and the cases considered in the calculations will be discussed here.
The Effect of Duct Cross-Sectional Shapes on Metrological Performance of Ultrasonic Flowmeters
Authors: Gryshanova Iryna
Published: March 2009

This paper describes prospects of measuring range extension on transient and laminar flow regimes for ultrasonic time-of-flight flowmeters due to creation measuring ducts with special cross-sectional shapes. The appropriateness of this idea consists that the flow profile correction factor, which considers a difference between averaged fluid velocity along the path of ultrasound propagation and area-averaged fluid velocity is not identical for laminar, transitive and turbulent conditions. Even on the assumption of axially symmetric flows the correction factor changes more than on 25% at transition from one condition to another. In this connection there was an object in view how to eliminate the influence of a velocity profile on accuracy of ultrasonic flow measurements. For that computer models of ultrasonic meters with several variants of cross-sections have been developed and due to CFD techniques the flow profile sensitivities of various meter configurations are investigated in different Reynolds number flows. The selection of optimum shape of the measuring duct for ultrasonic flowmeters has been appraised based on getting of as much as possible stable correction factor in a wide flow range and the minimal pressure loss on a meter. Results show that ultrasonic flowmeters with specially designed duct shapes could be used for increasing accuracy of non-liquid meter calibration and also for elimination of the error caused by variations of hydrodynamic flow characteristics.
Motion of a Thrombus in Blood Flow Through a Stenosed Vessel
Authors: Tanaka M. , Ohta T. , Hagiwara Y.
Published: March 2009

A direct numerical simulation has been conducted for a laminar flow in a constricted tube with an immiscible droplet in order to investigate the phenomena which an viscoelastic object such as a thrombus causes when it passes through a stenosed vessel. An immersed-boundary method is used for simulating the flow inside the constricted tube, while the PLIC-VOF algorithm is used for tracking the droplet interface. We have focused on a neutrally buoyant droplet of a fixed size. It is found that the droplet shape strongly depends on the capillary number, while the droplet velocity mainly depends on the viscosity ratio between two phases. The drag force (or fluid resistance) associated with the flow inside the tube is found to increase due to the presence of the droplet at low capillary numbers and at high viscosity ratios. The drag fluctuates when the droplet passes through the constricted area. This is triggered by a relatively large fluctuation in the pressure drag.
CFD Study of Prospective 1st Stage Centrifugal Impeller Design
Authors: Panaiotti Sergey S. , Rohatgi Upendra Singh , Timuchev Sergey F. , Soldatov Vladimir A. , Chumachenko Boris N.
Published: March 2009

CFD analysis of two first-stage centrifugal impellers is undertaken with the main goal to obtain additional evaluation data regarding flow characteristics of the old first stage impeller design and in the proposed new cantilever impeller design. The new design is developed to reduce the 1st stage impeller cavitation erosion damage of a multistage centrifugal feed pump. This stage of work comprises computational tests of both impeller models under the same mode of operation, 3000 RPM and volumetric flow rate 0.0503 m3/s. Both impellers are planning to be tested experimentally. The inlet geometry for CFD tests is taken from the test facility draft. The outlet is made like a circular vaneless diffuser. In the old design, a hub developed upstream presents the through shaft. Computational results are compared with the head/efficiency data delivered by plane cascade theory. Computational data shows an advantage of the new design by head and efficiency although the efficiency level is underestimated. Computational data shows lower pressure zones in the proposed design are localized at the impeller inlet periphery, in the old design lower pressure zones spreads along the blade inlet height. Further computational test will be made for the whole geometry including the stage stator part and experimental validation of the proposed design will follow.
A Straight-Bladed Vertical Axis Wind Turbine With a Directed Guide Vane Row
Authors: Takao Manabu , Maeda Takao , Kamada Yasunari , Oki Michiaki , Kuma Hideki
Published: March 2009

A straight-bladed vertical axis wind turbine with a directed guide vane row has been proposed in order to enhance its torque. The experimental study of the proposed wind turbine was carried out by a wind tunnel with an outlet diameter of 1.8m. The tested rotor has some straight rotor blades with a profile of NACA0015, a radius diameter of 0.3 m and a height of 0.7 m. The guide vane row having 3 arc plates rotates around the rotor and is directed to the wind by aerodynamic force generated by tail vanes, so as to put the guide vane row in upstream of the rotor. As a result, the performance of the straight-bladed vertical axis turbine was improved by means of the directed guide vane row. Further, by the use of the guide vane row adopted in the study, the power coefficient of the proposed wind turbine was approximately 1.5 times higher than that of the original wind turbine which has no guide vane.
Measurement of Unsteady Aerodynamics Load on the Blade of Field Horizontal Axis Wind Turbine
Authors: Maeda Takao , Kamada Yasunari , Naito Keita , Ouchi Yuu , Kozawa Masayoshi
Published: March 2009

This paper describes an experimental field study of the rotor aerodynamics of wind turbines. The test wind turbine is a horizontal axis wind turbine, or: HAWT with a diameter of 10m. The pressure distributions on the rotating blade are measured with multi point pressure transducers. Sectional aerodynamic forces are analyzed from pressure distribution. Blade root moments are measured simultaneously by a pair of strain gauges. The inflow wind is measured by a three component sonic anemometer, the local inflow of the blade section are measured by a pair of 7 hole Pitot tubes. The relation between the aerodynamic moments on the blade root from pressure distribution and the mechanical moment from strain gauges is discussed. The aerodynamic moments are estimated from the sectional aerodynamic forces and show oscillation caused by local wind speed and direction change. The mechanical moment shows similar oscillation to the aerodynamic excepting the short period oscillation of the blade first mode frequency. The fluctuation of the sectional aerodynamic force triggers resonant blade oscillations. Where stall is present along the blade section, the blade’s first mode frequency is dominant. Without stall, the rotating frequency is dominant in the blade root moment.
3D Unsteady Turbulent Simulation of the Runaway Transient of the Francis Turbine
Authors: Li Jinwei , Wu Yulin , Liu Shuhong , Zhu Yuliang
Published: March 2009

Based on Reynolds-averaged continuity and Navier-Stokes equations, and moment equation of the rotational system in the accelerated rotational relative coordinate, the governing equations of the runner region are obtained. The runaway transient simulation of the Francis turbine based on HL220 is made with RNG k-ε turbulence model under 9 guide vane openings. The variation diagrams of volume discharge, moment, rotational speed, and efficiency with respect to time are gained. Through further analysis of simulation results the transient process curve as well as the flow pattern under 9 guide vane openings are obtained, and detailed analysis is focused on flow in the draft tube to obtain variation of pressure distribution on symmetry surface of the draft tube with respect to time and pressure fluctuation of all test points in the turbine. Comparison between simulation and experiment results shows that they both are in good agreement, and it demonstrates that variation of all the parameters of the hydraulic turbine can be forecast accurately during the transient process.
Theoretical and Numerical Study of Vortex-Wake Flow Generated From Stack of Rectangular Bodies
Authors: Alhussan Khaled
Published: March 2009

Flow over external bodies has been studied extensively because of their many practical applications. For example, flow past a rectangular bodies, usually experiences strong flow oscillations and boundary layer separation in the wake region behind the body. As a fluid particle flows toward the leading edge of a rectangular body, the pressure of the fluid particle increases from the free stream pressure to the stagnation pressure. The boundary layer separates from the surface forms a free shear layer and is highly unstable. This shear layer will eventually roll into a discrete vortex and detach from the surface. A periodic flow motion will develop in the wake as a result of boundary layer vortices being shed alternatively from either side of the rectangular shapes. The periodic nature of the vortex shedding phenomenon can sometimes lead to unwanted structural vibrations, especially when the shedding frequency matches one of the resonant frequencies of the structure. The work to be presented herein is a theoretical and numerical analysis of the complex fluid mechanism that occurs over stack of rectangular bodies for different number of rectangular bodies, specifically with regard to the vortex shedding and generation of wake. A number of important conclusions follow from the current research. First, study of the actual flow configuration over rectangular bodies offers some insight into the complex flow phenomena. Second, the characteristics of the vortex and wakes change considerably with the number of bodies.