bluuebunny/crossref_metadata_2025 huggingface dataset:
Airside Velocity Measurement Above the Wind-Generated Water Waves
Authors: Shaikh Nasiruddin , Siddiqui Kamran
Published: March 2009

An experimental study conducted to investigate the airside flow behavior within the crest-trough region over wind generated water waves is reported. Two-dimensional velocity field in a plane perpendicular to the surface was measured using particle image velocimetry (PIV) at wind speeds ranging from 1.5 m s−1 to 4.4 m s−1. The results show a reduction in the mean velocity magnitude when gravity waves appear on the surface. A sequence of consecutive velocity fields has shown the bursting and sweeping processes and the flow separation above the waves. The results also indicate that the flow dynamics in the crest-trough region are significantly different than that at greater heights. High level of turbulence was observed in this region which could not be predicted from the measurements at greater heights. Thus, it is concluded that the quantitative investigation of the flow in the immediate vicinity of the interface is vital for an improved understanding of the heat, mass and momentum exchange between air and water.
Technique on Flow Measurement and Its Application in Low Head and Large Discharge Pump Stations
Authors: Zheng Yuan , Zhao Zong-Yin , Fan Bo-Qin , Qu Bo
Published: March 2009

The accurate discharge measurement of single pump in low head and large discharge pump stations has been considered as a difficult problem for a long time. Recently, with the completion of some pump stations of South-to-North Water Transfer Project in China, many low head and large discharge pump stations completed with gradually contracted inlet conduit need high accuracy of discharge measurement which is necessary to optimize the operation of pump units, sum up the total discharge and get the efficiency of the pump stations. In this literature, problems came across from traditional measurement methods of discharge are given. These methods are including five-hole probe discharge measurement, discharge measurement using current meter and differential pressure transmitter measurement. Among all these methods, the measurement principle, performance, installation and application of 7510P portable ultrasonic flow-meter with multi-path ultrasonic are specially introduced. Generally speaking, the low head pump stations usually have the characteristic of irregular multi-culvert construction with short straight conduit and gradually contracted cross-sections along the flow direction, so the accurate discharge measurement is very difficult to process. By installing multi paths in conduit, adopting technique on installation elevation of international regulations on Gauss integration method which is also employed in calculating flow, the flow can be got. The number of acoustic paths is determined by conduit construction and hydraulic conditions. The arrangements of acoustic paths are placed in the mode cross-link. Then the discharge can be calculated through integrating the obtained velocity in corresponding cross-section. The installation of 7510P portable ultrasonic flow-meter mainly comprises three processes, including the installation of transducers, the arrangement of cables and its connection with flow-meter. Combining the measured discharge in Jiangdu No.2 Pump Station of the South-to-North Water Transfer Project in China, following conclusions are presented: it has well stability, good repeatability of measurement results, high measurement accuracy with the error around ±0.30%, high reliability and the flow-meter fits a wide range of discharge well. The successful application of 7510P ultrasonic flow-meter accumulates useful experience for discharge measurement of single unit of low head and large discharge pump stations and add a new method of accurate field discharge measurement of low head pump stations, meanwhile, it will play a constructive role in the design, construction and management of pump stations.
Research on the Mathematic Model of Air Valve
Authors: Zhang Jian , Hu Jianyong , Lu Weihua , Liu Deyou , Fan Boqin
Published: March 2009

Air valve is an important measure of water hammer protection in long water distribution system. Volume of air inflow and outflow, the maximum volume of air inflow, and air mass flow rate are not only relate to prefer choose of air valve type, but effect on the safety of water distribution engineering. So it is important to make a theoretical calculation of air valve precisely. Traditional mathematic model of valve assumes that air inflows and outflows the pipeline by isentropic process, then isothermal variation will occur. Though this model is simple in theory and its programming is easy, its two thermodynamic processes are not incongruous obviously which results in its physical achievement unexplainable theoretically. Because the isentropic process is reversible adiabatic and no heat exchange occurs, but achievement of isotherm process need heat exchange sufficiently. This paper raises a new mathematic model of air valve based on those models reported so far. The new model gives up the hypothesis of isotherm, and proves rationality of this model by mathematical induction. Calculation results of two mathematic models are compared by numerical analysis. This provides scientific basis for precise simulation of air behavior through air valve and prefer choose of air valve type in long distribution system.
Numerical Simulation of Bubbly Flow Around a Marine Propeller
Authors: Kawamura T. , Ito A. , Hinatsu M.
Published: March 2009

The reduction of propeller efficiency in a bubbly flow is numerically studied in this study. The model used is a two-fluid multiphase flow model of which the governing equations are the mass and momentum conservation of the mixture and the bubble phases. The validation of model was carried out using experimental data for a 2D hydrofoil. The results of the simulation were investigated in detail in order to explain the decrease of the propeller efficiency in bubbly flows. It was shown that bubbles are relatively accelerated around the leading edge of a hydrofoil or a propeller blade, and that the acceleration of liquid is reduced due to the bubble acceleration. This effect lowers the peak of the negative pressure at the leading edge resulting in the decrease in the lift and the increase in the drag coefficients. Finally the model was applied to the prediction of the propeller efficiency in bubbly flow, and the results agreed with the experimental results.
Measuring and Numerical Simulation of the Free Water Surface of the Open Pump Suction
Authors: Chen Gang , Wu Yulin , Fan Yi , Cao Guangjun , Xu Zhaofeng
Published: March 2009

Detailed measurements of the free water surface of the open pump suction were obtained by PIV system. A step was arranged in the rectangular section of the model open type suction passage. The data have been measured with different conditions, such as the height of step (hs), averaged velocity (v) near the entrance of the open type suction passage, and the water height (h) near the chest wall. The existence of the step influences the flow situation greatly, when hs is higher, the flow situation becomes more turbulent. Near the end edge of the step, there were obvious drops of the water surface. When flow-velocity becomes bigger and water depth decreases, the flowing situations become more turbulent. Also, we calculated the free water surface at the open pump suction passage using the VOF method and the calculated results were coincided with the experimental data obtained under the same conditions. The results showed that the usefulness of PIV in obtaining the free water surface and validated the numerical model in simulation the open pump suction.
On the Numerical Computation for a One-Dimensional Two-Phase Flow Equations
Authors: Zeidan D.
Published: March 2009

This paper describes the development of an approximate solution for the numerical computation for a one-dimensional two-phase flow equations. The equations include source terms which account for the relaxation of volume fraction and the interfacial fraction. A simple splitting numerical method, which handles separately the homogeneous and source terms problems, is used to compute approximations of the solutions. The homogeneous problem is solved numerically using Godunov methods of centred-type. This solution is then employed in the source terms problem to solve the general initial-value problem for the two-phase flow equations. Numerical results are presented demonstrating the complete approach. The results show that the interphase interaction through the source terms appearing in the equations.
PIV Measurements and CFD Analysis in an Axial-Flow Pump
Authors: Tang Fang-Ping , Liu Chao , Zhou Ji-Ren , Yang Hua , Cheng Li
Published: March 2009

In this study, an axial flow pump impeller without guide vanes is experimentally investigated. The impeller used in the experiments consists of four blades. The particle image velocimetry technique and a five-hole probe have been used. Measurements of flow velocities in the outer part of the impeller have been made. PIV measurements have been realized in 12 meridian planes between blade-to-blade for design and off-design operating conditions. The meridian velocity is obtained with phase averaged method and the total circumferential mean velocity is obtained with an arithmetical average over the 12 circumferential data. The calculation is based on the CFX-TASC flow CFD code solving the three-dimensional Reynolds-averaged Navier-Stokes equation with RNG k–ε model of turbulence. The paper focuses on the comparisons of the results. Difference for the flow field between numerical and experimental results is small at large and design flow rate, while big difference occurs at small flow rate. It indicates that the numerical model is not suitable for separation flow.
Hydrodynamic and Hydroacoustic Characteristics of the Flow Noise Simulator (Keynote)
Authors: Mori Takayuki , Naganuma Kenji , Kimoto Risa , Yakushiji Ryo , Nagaya Shigeki
Published: March 2009

The Flow Noise Simulator (FNS) is a new large and quiet cavitation tunnel constructed by Naval Ship Systems Research Center of TRDI/Ministry of Defense, Japan for naval hydrodynamic and hydroacoustic research. This paper describes several results obtained from the initial evaluation tests of the facility involving, 1) flow uniformity and turbulent intensity at the test section, 2) LDV (Laser Doppler Velocimetry, 3) High Reynolds number turbulent boundary layer on the test section wall, 4) Acoustic noise source detection capability of the hydrophone array.
Computational Analysis of Noise Sources Inside the High Speed Flow Over a Bump
Authors: Okamoto Kentaro , Nonomura Taku , Fujii Kozo
Published: March 2009

The aerodynamic noise sources around the three dimensional bump are studied. In this search, pressure fluctuation on the wall which effects interior noise is searched using ILES. The ratio of the bump diameter (D) and height (H) is D/H = 4. In front of the bump, the boundary layer thickness is half of the bump height. Reynolds number based on the bump height was 65000 and the free stream Mach number is 0.1. In flow boundary layer profile is given by using rescaling method and the laminar boundary layer is changed into turbulent boundary layer. Sixth-order-accurate compact scheme is used to represent spatial derivatives and six-order low pass spatial filtering procedure is utilized for removing numerical oscillations. First, instantaneous flow field is discussed. Second, characteristics of time average flow field, such as Cp distribution and stream line topology, are discussed. Third, spanwise velocity fluctuation and sound pressure level on the wall are discussed.
Unsteady Numerical Simulations of the Flow Related to the Unstable Energy-Discharge Characteristic of a Medium Specific Speed Double Suction Pump
Authors: Braun Olivier , Avellan Francois , Dupont Philippe
Published: March 2009

Regions of positive slope in the pressure-discharge characteristics can result in a reduction or even lack of damping of system instabilities. They are therefore one of the major concerns in design and operation of centrifugal pumps as they are limiting the admissible operating range. The considered preliminary hydraulic design of an industrial double suction pump of medium specific speed ν = 0.410 (0.205 per impeller side) shows a marked saddle in the energy-discharge characteristic associated to a sudden drop of efficiency versus discharge at part load. Unsteady RANS type flow simulations are performed using hexahedral meshes with 2.5 million nodes to model the inlet casing, the shrouded double sided impeller with 2 × 7 blades, the diffuser with 12 blades and the volute. In unsteady solution monitoring, low frequency (below blade passing frequencies) phenomena are noticed. Therefore, simulation times of up to 10 impeller revolutions at each flow rate are requested to achieve statistically steady behavior of the flow judged on global performance numbers and circumferential flow rate distribution. The numerical simulations emphasize a drop in the characteristic, though at a lower flow rate than found on the test rig. It is shown to be associated to a one-sided separation in the diffuser, further leading to an unbalanced flow rate distribution of about 10% of flow rate between both sides of the impeller. There is a region of hysteresis, where both configurations with balanced and unbalanced flow rate distributions can be obtained for the same global flow rate. The asymmetric flow distribution leads to asymmetric velocity profiles at the impeller-diffuser interface which results in a strongly vortical flow in the diffuser channels, where an important amount of energy is dissipated in regions of increased viscous and turbulent shear.
Applications of Microfluidic Technology
Authors: Nagaoka Yoshihiro , Nishijima Noriyo , Koide Akira , Inami Hisao , Miyake Ryo
Published: March 2009

We have developed products that apply microfluidic technology to various fields: micro-mixing servers used in the chemical development field and in the personal products industry such as perfume and cosmetics; water quality monitoring systems for monitoring water quality items in tap water systems; bio-detection systems for monitoring bacillus content in air. This technology has the advantages of quick, easy use, and efficient processing due to quicker reactions, but it is not yet widely used. For such technology to be adopted, bonding technology that can quickly bond general resin materials and surface reforming technology for obtaining long-term stability is extremely important.
Cavitation in Ka´rma´n Vortex Shedding From 2D Hydrofoil: Wall Roughness Effects
Authors: Ausoni Philippe , Farhat Mohamed , Avellan Franc¸ois
Published: March 2009

The present study deals with the shedding process of the Ka´rma´n vortices in the wake of a NACA0009 hydrofoil at high Reynolds number, Reh = 25·103 − 65·103. This research addresses the effects of the foil leading edge roughness on the wake dynamic with a special focus on the vortex shedding frequency, vortex-induced vibration and three-dimensionality of vortex shedding. For smooth leading edge, the shedding frequency of Ka´rma´n vortices occurs at constant Strouhal number, St = 0.24. The wake exhibits 3D instabilities and the vortex induced vibration signals strong modulation with intermittent weak shedding cycles. Direct relation between vibration amplitude and vortex spanwise organization is shown. In the case of rough leading edge, the Ka´rma´n shedding frequency is notably decreased compared to the smooth one, St = 0.18. Moreover, the vortex induced vibration level is significantly increased and the vibration spectra sharply peaked. The occurrence of vortex dislocations is shown to be less frequent with the roughness. The shedding of the vortices is considered on the whole as in phase along the hydrofoil span. Obviously, the shedding process of the Ka´rma´n vortices is highly related to the state of the boundary layer over the entire hydrofoil. It is believed that in the case of smooth leading edge, slight spanwise non-uniformities in the boundary-layer flow lead to slight instantaneous variation in vortex shedding frequency along the span which is enough to trigger vortex dislocations. On the contrary, for the rough leading edge, the location of transition to turbulence is uniformly forced which leads to the reduction of the spanwise boundary-layer non-uniformities and therefore to the enhancement of the coherence length of the Ka´rma´n vortices.
Computational Aeroacoustic Analysis of Overexpanded Supersonic Jet Impingement on a Flat Plate With/Without Hole
Authors: Kawai Soshi , Tsutsumi Seiji , Takaki Ryoji , Fujii Kozo
Published: March 2009

Aeroacoustic mechanisms of an axisymmetric over-expanded supersonic jet impinging on a flat plate with and without hole are numerically investigated. High-order weighted compact nonlinear scheme is used to simulate the unsteady flow including shock waves and sound radiation in the near field of the jet. Analyses of unsteady flowfield and related near-sound field reasonably identify three major noise generation mechanisms, that is, noises from Mach wave, shock cell-shear layer interaction and small fluctuations of jet shear layer. Especially, intense noise radiation in the form of Mach waves and its reflection at the plate predominates the noises from the other two finer sources. The simulated distributions of sound source power and its frequency along the jet axis qualitatively well coincide with typical experimental data used in NASA SP-8072. Similar sound pressure spectrum shape is obtained both the cases of flat plate with and without hole, but the case of without hole shows higher SPL by several dB than that of with hole due to the stronger Mach wave radiation. Aeroacoustic flowfield is drastically affected by the Reynolds number because the jet shear layer instability directly causes the strength of acoustic waves.
The Effect of Boundary Layer Separation on Accuracy of Flow Measurement Using the Gibson Method
Authors: Sierra F. Z. , Adamkowski A. , Urquiza G. , Kubiak J. , Lara H. , Janicki W.
Published: March 2009

The Gibson method utilizes the effect of water hammer phenomenon (hydraulic transients) in a pipeline for flow rate determination. The method consists in measuring a static pressure difference, which occurs between two cross-sections of the pipeline as a result of a temporal change of momentum from t0 to t1. This condition is induced when the water flow in the pipeline is stopped suddenly using a cut-off device. The flow rate is determined by integrating, within a proper time interval, the measured pressure difference change caused by the water hammer (inertia effect). However, several observations demonstrate that changes of pipeline geometry like diameter change, bifurcations, or direction shift by elbows may produce an effect on the computation of the flow rate. The paper focuses on this effect. Computational simulations have shown that the boundary layer separates when the flow faces sudden changes like these mentioned to above. The separation may reduce the effective cross section area of flow modifying a geometry factor involved into the computation of the flow rate. The remainder is directed to quantify the magnitude of such a factor under the influence of pipeline geometry changes. Results of numerical computations are discussed on the basis of how cross section reductions impact on the geometry factor magnitude and consequently on the mass flow rate.
Application of Interface-Tracking Method Based on Phase-Field Model to Numerical Analysis of Isothermal and Thermal Two-Phase Flows
Authors: Takada Naoki
Published: March 2009

For interface-tracking simulation of two-phase flows in various micro-fluidics devices, the applicability of two versions of Navier-Stokes phase-field method (NS-PFM) was examined, combining NS equations for a continuous fluid with a diffuse-interface model based on the van der Waals-Cahn-Hilliard free-energy theory. Through the numerical simulations, the following major findings were obtained: (1) The first version of NS-PFM gives good predictions of interfacial shapes and motions in an incompressible, isothermal two-phase fluid with high density ratio on solid surface with heterogeneous wettability. (2) The second version successfully captures liquid-vapor motions with heat and mass transfer across interfaces in phase change of a non-ideal fluid around the critical point.
Experimental Investigation of Turbulence Specifications of 3-D Density Currents
Authors: Firoozabadi B. , Afshin H. , Baghaer Poor A.
Published: March 2009

The present study investigates the turbulence characteristic of density current experimentally. The 3D Acoustic-Doppler Velocimeter (ADV) was used to measure the instantaneous velocity and characteristics of the turbulent flow. The courses of experiment were conducted in a three-dimensional channel for different discharge flows, concentrations, and bed slopes. Results are expressed at various distances from the inlet, for all flow rates, slopes and concentrations as the distribution of turbulence energy, Reynolds stress and the turbulent intensity. It was concluded that the maximum turbulence intensity happens in both the interface and near the wall. Also it was observed that turbulence intensity reaches its minimum where maximum velocity occurs.
Front Tracking Simulation of a Liquid Capsule Enclosed by an Elastic Membrane
Authors: Li Xiaoyi , Sarkar Kausik
Published: March 2009

Dynamics of a liquid capsule enclosed by an elastic membrane in a shear flow is investigated using front tracking finite difference method. We compute deformation, orientation and tank treading, as functions of forcing (capillary number) and viscosity ratio for two different membrane constitutive equations—Neo-Hookean and Skalak. The computed results compare very well with those obtained by high-order Boundary element methods as well as small deformation perturbation analysis. The simulation shows that a drop and a capsule, even under those circumstances that result in the same Taylor deformation criterion for both, attain very different shapes. The tank-treading period even for different capillary numbers as well as capsules with different constitutive laws, is determined by the deformation and the viscosity ratio.
A 3-D Numerical Modeling of Droplet Actuation via Electrowetting in Microchannels
Authors: Arzpeyma Alborz , Dolatabadi Ali , Wood-Adams Paula
Published: March 2009

Numerical investigation is performed to study the droplet behavior under electrowetting actuation inside microchannels. Volume of Fluid (VOF) technique is employed to track the interface while the electric field is solved inside the whole domain in each time step simultaneously. The equations are solved in three dimensions for water as the liquid phase. Droplet morphology under the application of an electric field is investigated. Droplet velocity studied under different actuation voltages and compared to the experiments. Contact angle hysteresis and its effects on the threshold voltage are discussed.
Examination of Heating and Cooling Function in Nasal Cavity That Applies Heat Conduction Model to Inner Wall
Authors: Watanabe Masahiro , Horiuchi Yuji , Nakayama Toshio , Ishikawa Shigeru , Matsuzawa Teruo
Published: March 2009

Heating is a main function of a nose. The most important contribution to this function is made by the upper respiratory tract before the air reaches the laryngotracheal region [1]. The examination of the temperature distribution in the nasal cavity by the measurement and numerical analysis was done in previous research [1–3]. However, accurate measurement of the temperature distribution in nasal cavity is technically difficult, and there isn’t the research of numerical simulation about the distribution of the temperature on the wall including the inflow temperature influence. In this study, we set the temperature condition in inner wall, and we used the heat conduction model to inner wall. The heat source is a blood that surrounds the nasal cavity. It exists in the nasal cavity wall. The temperature distribution inside the nasal cavity or on the surface of the boundary wall was examined. Moreover, the nasal cavity shape was restructured with the medical CT images of the volunteer. So far, we have examined the flow in the nasal cavity according to the nasal cavity shape restructured with the CT images [4]. In result, we showed that air was heated enough by the temperature of wall and the result by the heat conduction model showed a good agreement with the measurement result of the research of Keck [1]. In addition, because flow velocity was different with the right and left nasal cavity, the temperature distribution of a right and left nasal cavity was different. Moreover, the flow profile and the temperature distribution depended on each volunteer’s shape and were different.
Shadowgraphic Analysis and Speckle Photographic Measurement of a Micro Shockwave Induced by Laser Irradiation on a Metal Surface
Authors: Fujinami Masaru , Hirahara Hiroyuki , Kawahashi Masaaki
Published: March 2009

Laser induced streaming is one of the interesting phenomena. When we provide a highly concentrated energy in a small region by laser beam, an induced streaming, such as micro shock wave or laser induced thermal acoustics is observed in the test region. In the present paper, a micro shock wave in air which was induced by laser irradiation was observed by shadowgraphic technique, and the shock Mach number was measured from the flow images. The induced density behind the shock wave was measured by speckle photographic technique. While the induced shock wave is produced in general by the ablation of a metal or gas breakdown due to the high density energy of laser irradiation, the present paper focused on relatively low density energy domain. As the laser power decreasing, the plasma was not observed in the test field but the micro shock still induced. The Mach number of this shock wave was measured by shadowgraphic images. For the shock measurement, a speckle photographic observation was carried out to obtain the density distribution behind the shock wave. The shock Mach number and density distribution was compared with self-similar solution in the moderate range of laser irradiation.
Three-Dimensional Structure of Separated and Vortical Flow in a Half-Ducted Propeller Fan
Authors: Jeong J. H. , Takahashi K. , Iwakiri K. , Furukawa M.
Published: March 2009

Three-dimensional structure of separated and vortical flow field has been investigated by numerical analysis on a half-ducted propeller fan. Complicated flow phenomena in the fan were captured by the Reynolds-averaged Navier-Stokes flow simulation (RANS) and a vortex structure identification technique based on the critical point theory. The flow field around the fan rotor is dominated by the tip leakage vortex. The tip leakage vortex starts to be formed near the blade mid-chord and grows nearly in the tangential direction without vortex breakdown. In the rotor passage, the high vorticity flow around the tip leakage vortex core is impinging on the pressure surface of the adjacent blade. It is expected that the behavior of the tip leakage vortex plays a major role in characteristics of the fan noise.
A High-Order Overset-Grid Approach for Large Eddy Simulations
Authors: Sherer Scott E. , Visbal Miguel R. , Gordnier Raymond E.
Published: March 2009

A parallel, high-order, overset-grid method is validated for use in large eddy simulation (LES) through its application to turbulent flow problems. The current method employs a high-order, compact finite-difference approach to evaluate spatial derivatives, with up-to-tenth-order low-pass filters used to remove high-frequency spurious wave content. These filters have also been found to be effective in modeling the dissipation that occurs at the unresolved scales in the flow for LES simulations. Temporal integration is based on an implicit, approximately-factored and diagonalized, second-order algorithm, which reduces the time-step constraints present in explicit time-marching methods for wall-bounded viscous flows. Parallelization, geometric complexity, and local grid refinement are all addressed through the use of an overset-grid approach, with grid communication provided by high-order Lagrangian interpolation. Problems demonstrating this approach include fully turbulent channel flow and flows over a single circular cylinder, a general delta-wing configuration, and a realistic UAV geometry.
Turbulence Measurements in Channel Flows With Rough and Hydrophobic Walls
Authors: Ahmad N. , Parthasarathy R. N.
Published: March 2009

Particle Image Velocimetry (PIV) measurements were made in a fully-developed turbulent channel flow. The channel test section was 1 ft wide and 1 inch in height and was constructed out of plexiglass. One wall of the test section was made removable. Four walls were used: a plexiglass smooth wall, and three hydrophobic walls: (i) a lotus paint coated plexiglass wall, (ii) a treated aluminum sheet attached to the plexiglass wall and (iii) a treated rough surface attached to the plexiglass wall. The bulk velocity was held constant to yield a Reynolds number (based on the channel half-height) of 5,500. Several images were averaged to obtain mean velocity and Reynolds shear stress and turbulence kinetic energy measurements. It was found that the mean velocities in the near-wall region were higher for the lotus-paint coated surface flow and the treated rough surface flow than the flows with the other two surfaces. The friction velocity estimated from the Reynolds shear stress measurements was significantly lower for these two flows as well. The reduction in the wall shear stress in these flows is attributed to the finite slip that occurs at the hydrophobic surfaces.
Motion of Swirling Vortex Generated From Sharp Edge
Authors: Shigefuji H. , Shimizu F. , Tanaka K. , Tokuda K.
Published: March 2009

The siphon phenomenon is widely used for the transportation system of water and it is very economical and ecological because the natural energy of water is only used for the power source of the transportation system. The siphon phenomenon is continued while the water is supplied with from the entrance, and a large-scale separation flow forms near the entrance of a siphon tube. The appearance, the growth, the movement and the disappearance of a swirling vortex are observed inside the siphon tube, and the flow field near the entrance becomes very complex. In the present paper, the flow pattern behind a sharp edge of the entrance was investigated experimentally using the PIV measurement.
High Speed Flow Visualisation of an Impinging Jet on a Pelton Turbine Bucket
Authors: Perrig Alexandre , Farhat Mohamed , Avellan Franc¸ois
Published: March 2009

This paper deals with flow investigations using endoscopes in a single-injector reduced scale Pelton turbine performed with a CMOS high-speed camera. Both onboard and external visualizations techniques of the flow in a bucket are presented. The flow observations evidence the unsteadiness of the successive steps of jet/bucket interaction, free surface flow development and evolution throughout the bucket duty cycle.
Assessment of Partially Averaged Navier Stokes (PANS) Multiscale Model in Transonic Turbulent Separated Flows
Authors: Basu D. , Hamed A. , Das K.
Published: March 2009

This paper presents an assessment of Partially Averaged Navier Stokes (PANS) model in transonic separated turbulent flow simulations. The two-equation k-ε based PANS models are implemented in a full 3-D Navier-Stokes solver and numerical results are obtained for transonic flow solution over an open cavity using a 3rd order Roe scheme. Results for the vorticity, pressure fluctuations, SPL (Sound Pressure level) spectra and for resolved TKE (Turbulent Kinetic Energy) are presented and compared with available experimental data and LES results. The effect of the PANS model variable fk (unresolved kinetic energy parameter) on the flow and acoustic field of the cavity is also analyzed. Computed results show that the predicted dominant frequency and the peak amplitude in the SPL spectra are influenced by the model constant.
Modeling and Analysis of Spherical Pulsation Dampeners in Fluid Power Systems
Authors: Duan Shanzhong , Gamal Mutasim E.
Published: March 2009

This paper presents a new method for computer-aided modeling and analyzing of pulsation dampeners used in fluid power systems for vibration reduction. The pulsation dampeners are widely used in various fluid power systems to reduce vibration induced by power pumps. The vibration induced by power pumps in fluid systems may be severe enough to cause the damage of components in pipelines if a pulsation dampener is not installed. However, the current methods used in industries for the design and analysis of the dampeners are manually experience-orientated procedures. They are not adaptable to new technologies. The new modeling method will efficiently automate and improve the current modeling and analysis procedure of various pulsation dampeners with a minimum user effort. The proposed method is a result of utilizing the analogy between electrical circuits and hydraulic circuits. In the new method, a spherical pulsation dampener can be equivalent to a lumped hydraulic circuit installed in a distributed fluid pipeline system. In short, the new method will circumvent some obstacles and introduce new techniques for computer-aided modeling and designing of the dampeners for vibration reduction in fluid power systems.
Using Change Point Analysis for Image Processing of Developing Adiabatic Two-Phase Flow After Expansion Valve
Authors: Bowers Chad D. , Hrnjak Predrag S.
Published: March 2009

This paper presents a method of analyzing images obtained from a high speed camera in a study of developing two-phase refrigerant flow after an expansion valve, using a technique known as Change Point Analysis. Specifically, a method for automating the determination of separation distance and the location of the liquid/vapor interface in stratified type flows is outlined. The experiments were conducted in transparent PVC tubes, with inner diameters of 8.7mm and 15.3mm. A working fluid of oil free R134a was used. Dynamic flow parameters of inlet quality and mass flux were varied from 5–35% and 15–40g/s, respectively. Flow visualization was achieved through the use of a high speed camera.
A Three-Dimensional Transient Numerical Study of a Close-Coupled Catalytic Converter Internal Flow
Authors: Ramadan Bassem H. , Richmond Russel L.
Published: March 2009

This study involves a numerical and experimental investigation of fluid flow in automotive catalytic converters. The numerical work involves using computational fluid dynamics (CFD) to perform three-dimensional calculations of turbulent flow in an inlet pipe, inlet cone, catalyst substrate (porous medium), outlet cone, and outlet pipe. The experimental work includes using hot-wire anemometry to measure the velocity profile at the outlet of the catalyst substrate, and pressure drop measurements across the system. Very often, the designer may have to resort to offset inlet and outlet cones, or angled inlet pipes due to space limitations. Hence, it is very difficult to achieve a good flow distribution at the inlet cross section of the catalyst substrate. Therefore, it is important to study the effect of the geometry of the catalytic converter on flow uniformity in the substrate. The analysis involved determining back pressure (BP) across the converter system for different monolith cell densities, mass flow rates, converter aspect ratio, inlet cone angle, and inlet pipe offset. The numerical results were used to study the velocity profile at the inlet to the substrate, and were verified with experimental measurements of velocity and BP.
Modeling and Analysis of Spool Valves With Eccentric Clearance
Authors: Duan Shanzhong , Nielsen Tyler
Published: March 2009

Equations of motion of spool valves have been set up under ideal conditions without considering some important factors that may have a significant influence on dynamical behavior and performances of spool valves especially when valve sizes are small. In this paper, these factors are brought into considerations. One of them is the eccentric clearance existing between the spool and the sleeve of a valve due to fabrication errors. Another is the viscosity of a Newtonian fluid assumed to flow through the valve orifices, which generally results in shear forces acting on the valve spool. This paper discusses how equations of motion of spool valves are derived and solved with considerations of these factors. Concepts of Poiseuille flow and Couette flow are utilized to obtain axial forces acting on the valve spool. The resulting equations of motion of spool valves have the simple form of a second order linear ordinary differential equation under the imposed idealizations. The influences of these factors on the motion behavior of spool valves are in turn discussed.
Analysis of Sauter Mean Diameter (SMD) for Fuel Sprays
Authors: Jawad Badih A. , Riedel Chris H.
Published: March 2009

The spray-tip penetrations and the drop sizes of intermittent fuel sprays were measured by using a modified pulsed optical spray sizer. The average spray tip speeds were determined from simultaneously recorded needle lift signals and obscuration traces. The speeds of a sequence of fuel pulses injected at ∼103 Hz were analyzed to elucidate penetration mechanisms. A correlation that relates penetration distance to time, pressure drop across the nozzle, fuel density, and ambient gas density was obtained. The temporal variations of drop size in penetrating pulses of sprays were measured. The concentration of drops were calculated by combining drop size and obscuration data. The Sauter mean diameter of penetrating fuel drops increased with an increase of the chamber pressure and decreased with an increase of the injection pressure.
Turbulent Statistics of Nearly Isotropic Turbulence Generated by Four Rotating Grids and the Mean Falling Velocity of Particle Through Turbulence
Authors: Ushijima Tatsuo , Kitoh Osami
Published: March 2009

Box air turbulence is experimentally generated in a rectangular box by using four counter-rotating grids installed inside. Turbulence statistics are obtained from one-point measurement of LDA. Nearly isotropic turbulence with zero-mean velocity is realised in the midst of four rotating grids. The dissipation rate is estimated from the Taylor time microscale of velocity autocorrelation obtained from LDA measurement, since Taylor’s frozen turbulence hypothesis is not applicable. From this estimation, the Reynolds number based on the Taylor length microscale becomes about 200 at maximum in the present experimental apparatus. The mean falling velocity of small particle in turbulent flow is measured in the box turbulence. It is found that the mean falling velocity of the inertia particle could be smaller or larger than the terminal velocity, depending on the particle property, if the ratios of particle response time to turbulence time scale are the same.
Wind Turbine Blade Flow Fields and Prospects for Active Aerodynamic Control
Authors: Schreck S. , Robinson M.
Published: March 2009

As wind turbines continue to grow larger, problems associated with adverse aerodynamic loads will grow more critical. Thus, the wind energy technical community has begun to seriously consider the potential of aerodynamic control methodologies for mitigating adverse aerodynamic loading. Spatial and temporal attributes of the structures and processes present in these flow fields hold important implications for active aerodynamic control methodologies currently being contemplated for wind turbine applications. The current work uses complementary experimental and computational methodologies, to isolate and characterize key attributes of blade flow fields associated with axisymmetric and yawed turbine operation. During axisymmetric operation, a highly three-dimensional, shear layer dominated flow field yields rotational augmentation of both mean and standard deviation levels of aerodynamic forces. Under yawed operating conditions, pseudo-sinusoidal inflow angle oscillations elicit dynamic stall, which significantly intensifies aerodynamic load production. Both rotationally augmented and dynamically stalled flows possess attributes likely to pose central challenges for turbine flow control. Whether active control of turbine aerodynamics can help alleviate adverse aerodynamic loads will depend on comprehension and command of the issues documented herein.
PIV and PLIF Measurements of Model Urban Flows in a Water Channel
Authors: Pan Hansheng , Li Xiangyi , Princevac Marko
Published: March 2009

Systematic and hierarchical water channel experiments were conducted with the goal of obtaining better understanding of complex urban flows. Particle Image Velocimetry (PIV) together with Planar Laser Induced Fluorescence (PLIF) were used for comprehensive flow and concentration measurements within a modeled urban setup. Mock urban settings were reproduced using acrylic blocs whose refraction index is the same as the refraction index of salty water. Such setup allowed for undisturbed laser sheet illumination through the obstacles enabling detailed measurements between the obstacles (mock buildings). Building array size, measurement plane and flow conditions were systematically varied. Challenges and benefits of using transparent materials with the laser based flow measurements will be outlined. Novel flow features observed and quantitatively measured within the complex mock urban settings will be presented and discussed. It was found that lateral array size has significant influence on initial dispersion within the array. Smaller array size lead to sideways flow channeling causing significant plume spread. This sideways channeling becomes less pronounced as array size increases.
A Study on the Induced Liquid Velocity in Plumes by Tiny Bubbles
Authors: Gong Xiaobo , Takagi Shu , Matsumoto Yoichiro
Published: March 2009

The effect of the bubble-induced liquid velocity on the mass transfer performance in the bubble plume is analyzed quantitatively with numerical simulations. A two-way coupling Eulerian-Lagrangian approach is used in the modeling of the bubble plumes with mass transfer. The dissolution of oxygen in bubble plumes with the initial bubble diameters from 100μm to 1mm is simulated. The results show that when a single bubble generator is used with the gas flux rate equals 10−8 cubic meter per second, for the plume with 100μm bubbles inside a 0.1m height cubic tank the maximum of the bubble-induced liquid velocity is over 10 times larger than the bubble’s terminal velocity, and the averaged residence time of bubbles in the plume is around one-tenth of the rising period estimated with the terminal velocity of a single bubble. The result suggests that for bubble plumes in a shallow bulk of water, the benefits of using smaller bubbles for high mass transfer efficiency will be overestimated without considering the reduction of the residence time of bubbles because of the bubble-induced liquid velocity. The present simulation shows that the dissolution efficiency of oxygen for the bubble plume with 100μm bubbles in 0.1m tank is around 1/2 of the theoretical value estimated with a single bubble rising with negligible diameter shrink. Compared with a plume in a 0.1m tank, the shrink of bubble diameter and the scattering of bubbles from the center of plume during their rising in a 0.4m tank attenuate the reduction of the averaged residence time because of the acceleration process as shown in a 0.1m tank. The effect of bubble-induced liquid velocity on the mass transfer efficiency for plumes with initial bubble diameter smaller than 160μm does not present obviously in a 0.4m tank as it does in the shorter tank.
Rheological Properties of Emulsions Immersed in Electric Fields
Authors: Ferna´ndez Arturo
Published: March 2009

The results of fully three-dimensional direct numerical simulations of the effects of electric fields on emulsions of drops will be displayed. The examination of the rheological properties of these systems is performed by imposing a simple-shear flow between two plates where the drops are immersed. An electric potential difference is applied perpendicular to the plates. The resulting electric field leads to two effects: a polarization of the drops and a viscous fluid motion on the interface between the drops and the suspending fluid. The direction and intensity of the viscous fluid motion depends on the electrical properties of the fluids. Drops more conductive than the suspending fluid exhibit a viscous fluid motion from the equator to the poles, whereas drops less conductive than the suspending fluid exhibit a viscous fluid motion from the poles to the equator. The numerical simulations show that the response of the emulsions is governed by the competition between the electric attraction and the fluid shear. The former leads to the aggregation of the drops in chains parallel to the electric field, while the latter tries to break-up the aggregated chains. The results are presented as a function of the Mason number and the electric capillary number, Mn and Ce. These non-dimensional numbers quantify the strength of the electric forces versus the fluid shear and the capillary forces, respectively. The significance of the electrical field on the viscosity and the normal stress differences will be discussed: At low Mason numbers, Mn<0.1, the application of the electric field results in the aggregation of the drops. This aggregation leads to an increase in the effective viscosity of the system and to an increase in the stresses, which result in higher normal stress differences than in hydrodynamic emulsions. At high Mason numbers, Mn>1.0, the fluid shear breaks up the aggregated structures and the properties are similar to hydrodynamic emulsions. At 0.1<Mn<1.0 the properties of the emulsions exhibit an intermediate behavior.
Relationship Between Vibrations and Mechanical Seal Life in Centrifugal Pumps
Authors: Leishear Robert A. , Stefanko David B.
Published: March 2009

A reduction of vibrations in mechanical seals increases the life of the seals in centrifugal pumps by minimizing fatigue damage. Mechanical seals consist of two smooth seal faces. One face is stationary with respect to the pump. The other rotates. Between the faces a fluid film evaporates as the fluid moves radially outward across the seal face. Ideally, the film evaporates as it reaches the outer surface of the seal faces, thereby preventing leakage from the pump and effectively lubricating the two surfaces. Relative vibrations between the two surfaces affect the fluid film and lead to stresses on the seal faces, which lead to fatigue damage. As the fluid film breaks down, impacts between the two seal faces create tensile stresses on the faces, which cycle at the speed of the motor rotation. These cyclic stresses provide the mechanism leading to fatigue crack growth. The magnitude of the stress is directly related to the rate of crack growth and time to failure of a seal. Related to the stress magnitude, vibration data is related to the life of mechanical seals in pumps.