bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion of Spilled Heavy Oil by Impinging Water Jet
Authors: Iwasaki Akinori , Kato Hiroharu
Published: March 2009

The purpose of this study is searching for a new method of dispersing spilled heavy oil, which has a detrimental effect on the natural environment and the ecosystem of the sea. A method ejecting a water jet vertically downward to heavy oil on the water surface was discussed. The water jet involved the heavy oil and the minute air bubbles, and passed the nozzle of the guide plate. The shapes of the nozzles of the guide plates were three types; a conventional column, a 5 times length column, and a taper. The dispersion efficiency of the taper type nozzle was the best among three. The flow in the nozzle of the three guide plates were recorded by a high-speed camera. From the high-speed moves, the occurrence of two flows, regular and counter flow, was suspected in the taper guide plate. In addition, it seemed that the two flows occurred the sharing force between the minute air bubbles. It is considered that the sharing force invent the surplus efficiency of disperse.
LES for Soot Formation in a Propane-Air Turbulent Flame
Authors: Paul Sreebash C. , Paul Manosh C. , Jones William P.
Published: March 2009

Large Eddy Simulation (LES) technique is applied to investigate the Soot formation in a model cylindrical combustor. 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 based on the conserved scalar approach with laminar flamelet model, while the Soot formation is included through the balance equations for soot mass fraction and soot particle density. 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 which contain most of the turbulent energy are resolved explicitly while the unresolved small scale eddies are modelled via sub-grid scale (SGS) modelling approach.
Measurement of the Acceleration Field of the High-Speed Jet Sound Producing Region
Authors: Pinier Jeremy T. , Glauser Mark N.
Published: March 2009

With the aim of being capable of controlling the sound created by high-speed jets or engine exhausts, a preliminary experiment, using a near-field azimuthal array of 15 pressure sensors and a far-field array of 6 microphones, pointed out the region of highest sound production in the turbulent flow where a dual-time particle image velocimetry (DT-PIV) investigation is now being carried out. This measurement technique enables access to time-derivatives of the velocity field which is a quantity of great interest for developing prediction capabilities crucial for closed-loop flow control. Jointly, a flow control device using synthetic jets is developed and PIV measurements are taken with and without the control to assess the effectiveness of such devices for aeroacoustic flow control.
Experimental Investigation of the Effects of Surfactants on the Mass Transfer in Liquid-Liquid Extraction Equipments
Authors: Haghdoost A. , Shah-Alami M. , Mansouri H.
Published: March 2009

Mass transfer rates to the drops in liquid-liquid extraction equipment are often likely to be reduced by the presence of surface active contaminants. This reduction in mass transfer is said to be due to a reduction in terminal velocity, and to changes in pattern of internal circulation. A single-drop extraction apparatus was used to investigate the dependency of mass transfer coefficient on the amount of surfactant added in a system of n-butanol/succinic acid/water. Three types of surfactants, SDS, DTMAC and Triton X-100, were used to study their effects on the inhibition of mass transfer in liquid-liquid extraction. The effect of surfactants concentration on extraction percentage, overall mass transfer coefficient, and extra mass transfer resistance was investigated for these surfactants. Also variation of terminal velocity as a function of surfactant concentration and drop diameter were illustrated for both surfactants. Finally these surfactants were compared to each other.
Numerical Investigation of Erosion Phenomena in Curved Ducts
Authors: Ibrahim K. A. , El-Kadi M. A. , Hamed Mofreh H. , El-Behery Samy M.
Published: March 2009

Solid particle erosion is a complex phenomenon that depends on many factors such as particle and flow characteristics, type of material being eroded and flow geometry. Bends, which are integral parts of piping system, are vulnerable in erosive environments because solid particles can not follow the streamlines of the flow and impinge on the pipe wall. Thus, this paper investigates numerically the erosion phenomenon that occurs in 90° and 180° curved ducts. The numerical calculations are performed by Eulerian approach for gas-phase taking into account the mutual effects of the solids on the gas and Lagrangian approach for dispersed-phase. 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 erosion prediction model comprises three stages: flow modeling, particle tracking and erosion calculations. Many of the previous published data are taken to validate the three stages of the present model. Comparisons between predicted penetration rate and published experimental data show a good agreement. The effects of bend orientation, inlet gas velocity, bend dimensions, loading ratio and particle size on the penetration rate are also simulated. The present results show that the penetration rate increases as the curvature ratio, particle diameter, inlet gas velocity increase and as the mass loading ratio and pipe diameter decrease. Furthermore, the present results show also that the bend orientation and flow direction have no significant effect on the penetration rate.
A Scaling Law for Cavitation Inception in Circular Jet Flows
Authors: Edge Brian A. , Paterson Eric G. , Trujillo Mario F.
Published: March 2009

The historical data for circular jets indicates that the incipient cavitation number increases with the diameter of the jet. This trend is not explained by the classic cavitation theory which expects incipient cavitation number to remain constant regardless of the jet diameter, flow parameters, or water quality. This paper explores the origins of cavitation scale effects and explains the correlation between the incipient cavitation number, jet diameter, and nuclei size. This is accomplished through turbulence-resolving CFD simulations of the jet flow field at three length scales and Rayleigh-Plesset bubble dynamics for three nuclei sizes. The numerical simulations show that incipient cavitation number (σi) changes significantly as the size of the jet is altered while the Reynolds number and the value of the minimum pressure coefficient are held constant. Larger nuclei bubbles (100μm) exhibit an increase in σi with jet diameter, while moderate (50μm) and small (10μm) nuclei bubble exhibit a decrease in σi as jet diameter increases. The value of σi associated with a small jet was similar for all nuclei sizes. As the jet increased in size, the disparity between the values of σi associated with each nuclei size was found to increase substantially. The equilibrium form of the Rayleigh-Plesset equation was used to derive a correction to the classic theory of cavitation inception. This correction is a function of initial nuclei size and the dynamic head of the flow. As either the nuclei properties or dynamic head of the fluid change, the magnitude of the correction term will also change. This correction to the classic cavitation theory was used to make predictions of how σi will change as length scale and Reynolds number are altered. These equilibrium predictions were found to be in good agreement with the numerical simulations of cavitation inception for large and moderate (100μm and 50μm) nuclei bubbles. Comparisons with the small (10μm) nuclei bubbles indicate that the inertial terms are quite significant for these bubbles, resulting in large discrepancies between the full numerical solution and the equilibrium predictions. In general, the equilibrium scaling relations show that as the length scale of a flow is held constant and the Reynolds number is increased, σi will converge to −CPmin. The scaling relations also show that when Reynolds number is held constant and the length scale of a flow is increased, σi will depart from −CPmin.
Numerical Analysis of the Swirl Intensity Decay Rate for Internal Turbulent Swirling Flow
Authors: Najafi A. F. , Mousavian S. M. , Saidi M. H.
Published: March 2009

In this research the trend of swirl decay and factors influencing the turbulent swirl flows have been investigated in a fixed pipe. In this regard, turbulent swirling decay flow with solid body rotation has been numerically surveyed using different flow conditions at the pipe inlet. The numerical results have been validated and compared with the existing mathematical relations having satisfactory agreement. Results show that the swirl intensity decay rate has strong dependency on the Reynolds number. On this basis, correlations have been proposed which improves predictions of swirl intensity decay rate at upstream regions and those with high swirl intensity. In addition, analyses have been made to demonstrate that the previously developed correlations for predicting swirl intensity decay rate, agree with those provided in this study only for regions far enough down stream having the low swirl intensity. This implies that the swirl intensity decay rate should be a function of the type of swirl generator at the inlet.
Numerical Simulations of Gas-Liquid-Solid Flows in a Hydrocyclone Separator
Authors: Musavian S. M. , Najafi A. F.
Published: March 2009

The flow behavior in hydrocyclones is quite complex. The Computational Fluid Dynamics (CFD) method was used to simulate the flow fields inside a hydrocyclone in order to improve its separation efficiency. In the computational fluid dynamics study of hydrocyclones, the air-core dimension is a key to predicting the mass split between the underflow and overflow. In turn, the mass split influences the prediction of the size classification curve. Three models, the k–e model, the Reynolds stress model without considering air core and Reynolds stress turbulence model with VOF multiphase model for simulating aircore, were compared for the predictions of velocity, axial and tangential velocity distributions and separation proportion. The RSM with aircore simulation model, since it produces some detailed features of the turbulence and multi phase, is clearly closer in predicting the experimental data than the other two.
Boundary Layer Solution for Laminar Swirling Decay Pipe Flow
Authors: Ahmadvand M. , Najafi A. F. , Shahidinejad S.
Published: March 2009

In this study the hydraulic-thermal developing laminar swirling pipe flow is investigated numerically. Solution is based on the integral boundary layer method Uniform and solid body rotation distributions are considered for the axial and tangential velocities at the entry, respectively. Due to wall stress, viscous region is assumed to contain two boundary layers for axial and tangential velocities. Outside of the boundary layers’ edge the flow pattern is considered to remains uniform in axial direction and forced vortex in tangential direction. Inside boundary layers parabolic velocity and temperature profiles were considered for axi-symmetric flow pattern with uniform heat flux (UHF) condition on the pipe wall. Making use of the fourth-order Runge-Kutta scheme, the numerical solution of the governing differential equations is obtained. As an alternative solution, a CFD analysis based on the finite-volume method, has been done. Finally validity of the numerical results was checked with those obtained by CFD.
Interface Tracking With a Coupled Level Set /VOF/Ghost Fluid Method: Application to Jet Atomization
Authors: Me´nard T. , Berlemont A.
Published: March 2009

We are here concerned by the primary break-up of a jet: a lot of topological changes occur and the Level Set Method thus appears well designed for our purpose. To describe the interface discontinuities, we use the Ghost Fluid Method (GFM) and a projection method is used to solve incompressible Navier-Stokes equations that are coupled to a transport equation for the level set function. The main drawback of level set methods is that numerical computations in the re-distancing algorithm can generate mass loss in under-resolved regions. To improve mass conservation extension of the method can be developed, namely a coupling between VOF and Level Set. In order to illustrate the abilities of the Level Set/VOF/Ghost Fluid method for interface tracking, we present a 3D simulation of the primary atomization zone of a turbulent liquid jet. The turbulence initiates some perturbations on the liquid surface, that are enhanced by the mean shear and break-up occurs. The generated liquid parcels show a wide range of shapes. Particular behaviors such ligament detachments, droplet formations and break up are described.
Cavitating Vortex Flow Generated by a Stationary Volute Casing and a Rotating Centrifugal Impeller
Authors: Okamura Tomoyoshi , Kubota Jun , Yoshikawa Tatsuya
Published: March 2009

Three devices for treating contaminated water using a cavitating vortex have been developed and tested. The first device uses stationary twin volute casings to generate cavitating vortices. Observation of the collisions among the opposing counter-rotating vortices revealed that their end portions whirl, that the vortices never collide head-on, and that they eventually separate into several small vortex strings. The second device is simply half of the first device. A single volute casing is used, and the vortex flow collides with a solid wall. The third device uses a centrifugal impeller and a circular swirling chamber to generate a cavitating vortex. A high absolute circumferential velocity at the impeller exit induces a strong vortex in the chamber. The vortex cavitation is smoother than in the first two devices, and the end portion of the vortex whirls in the same manner as that generated in the first device. Installation of an orifice at the exit of the swirling chamber reduced the diameter of the flow passage and thereby accelerated the rotating and axial flow velocities. Testing showed that this third device produces fine, even-sized cavitation bubbles that are uniformly distributed in the collision chamber, which is the ideal condition for water treatment.
Usage of Axial and Rotating Magnetic Field to Process Ge0.98Si0.02 Crystal by the Traveling Heater Method
Authors: Jaber T. J. , Saghir M. Z.
Published: March 2009

A three-dimensional numerical simulation to study the effect of magnetic field on the fluid flow, heat and mass transfer is investigated. By applying axial and rotating magnetic field (RMF), an attempt was made to suppress the buoyancy convection in the Ge0.98Si0.02 solution zone in order to get homogeneity with flat growth interface. It was found that the intensity of the flow at the centre of the crucible decreased at a faster rate compared to the flow near the walls when increasing axial magnetic field intensity. This behaviour created a stable and uniform silicon distribution in the horizontal plane near the growth interface. Different magnetic field intensities for different rotational speeds (2, 7 and 10 rpm) were examined. The results showed that the RMF has a marked effect on the silicon concentration, changing it from convex to nearly flat when the magnetic field intensity increased.
3D-Numerical Simulation and Performance Predication of Vertical Axial Flow Pumping Station
Authors: Cheng Li , Liu Chao , Tang Fangping , Zhou Jiren , Yang Hua
Published: March 2009

In order to study flow pattern and hydraulic performance of vertical pumping station with bell inlet and worm outlet, which was used by South-to-North water transfers project, the incompressible N-S equations are solved by the control finite volume method. Based on the RNG k-ε model with Wall-Function Law, the SIMPLEC algorithm is applied for the solution of the discretization governing equations. Using multiple reference frames, the flow detail of whole vertical pumping system is attained. The named height of pump is put forward. The numerical hydraulic performance was computed. A good agreement was achieved between predicted data with experimental data on BEP. This type of pumping station will be applied in the East Route Project of South-to-North Water Transfers of China.
Mixing at Low Reynolds Numbers by Vibrating Cantilevered Ionic Polymers
Authors: Williams Alicia M. , Griffiths David R. , Vlachos Pavlos P.
Published: March 2009

The objective of this research was to develop a novel active device for laminar mixing. The mixing device developed herein capitalized on Nafion ionic polymers, which are a class of active materials that are thin, flexible, inexpensive, and readily deployable in an aqueous medium and offer strains up to 5% under a small (<2V) applied voltage. The effect of these deflections on an incident laminar flow is the mixing mechanism explored in this effort. To the author’s knowledge, this high-risk effort presented herein is the first attempt to exploit ionic polymers as an active mixing device. Several different configurations of ionic polymers were tested and Digital Particle Image Velocimetry (DPIV) measurements were obtained. Resulting analysis using a quantitative mixing metric shows that the polymer creates differences in the flow under some of the configurations. Namely, in some actuation cases, a clear increase in mixing potential is observed in the near-polymer regions. Compared to a simple channel increases in mixing potential that ranged from 150% to over 300% were measured. Although these differences are present, they do not appear consistently in the results. However, only a partial set of flow information was obtained from DPIV, and an improved understanding of the effect of these polymers could be developed from additional experiments. Using ionic polymers for laminar mixing could foster the development of a new generation of efficient micromixing devices, which will improve the capabilities and effectiveness of numerous microfluidic technologies that range across biomedical, lab-on-a-chip, separation and sorting technologies and many more.
Numerical Simulation of Pressure Fluctuation in Draft Tube of Large Francis Turbine
Authors: Liao Cuilin , Wang Fujun , Li Xiaoqin , Zhu Yuliang
Published: March 2009

The pressure fluctuation caused by swirling flow in draft tube is one of the main reasons of vibration in hydraulic turbine. It directly affects the steady operation of hydraulic turbine unit. The pressure fluctuation in draft tube of a large Francis turbine can’t be obtained accurately by similarity law from model test, and prototype test is difficult to carry out and costs too much. Therefore, it is necessary to predict pressure fluctuation in draft tube numerically and provide scientific reference for mitigating and suppressing pressure fluctuation. This paper describes a numerical study of unsteady flow in the draft tube of a large Francis turbine in a Hydropower Station of China by using the Reynolds averaged Navier–Stokes (RANS) approach with a Reynolds stress transport model (RSM), validating the numerical results against experimental data. The numerical results successfully represent the vortex rope. The pressure fluctuation patterns in different parts of the draft tube including the cone, elbow and diffuser are analyzed. The pressure fluctuation in the cone and elbow is relative steady, and it has an obvious dominant frequency which is approximately 0.28 and 0.3 times of the runner rotational frequency. These results show very good agreement with experiments. The largest pressure amplitude appears in the draft tube cone downstream side and the draft elbow inside. The pressure fluctuation in the diffuser is stochastic, and the amplitude is small. Additionally, the pressure distributions on the horizontal computational section of the draft tube are analyzed.
A Pressure-Based Two-Phase Flow Method for Computation of Bubble Cavitation Flows
Authors: Peng Guoyi , Egashira Ryu , Yano Takeru , Fujikawa Shigeo
Published: March 2009

A pressure-based two-phase flow method is proposed for computation of high-speed cavitation flows by coupling a Two-Fluids Three-Pressure bubble dynamics model and a compressible two-phase flow computation. The fluid mixture of two-phase media is composed of a liquid and spherical gas bubbles, those are supposed to disperse in the liquid phase uniformly. State equations of the liquid and gas phases are employed to relate their density with pressure, and the flow of two-phase mixture is then calculated by employing Navier-Stokes equations. Cavitation is evaluated by the volume fraction of gas phase and the average radius of cavitation bubbles in a local flow field is calculated by applying Rayleigh-Plesset equation. For simultaneous computation of above equations, a pressure-based predictor-corrector procedure is developed by applying CCUP method. As an example, flows in an orifice nozzle are treated and the reliability of computation is estimated by comparison with experimental data.
Effects of Tube Curvature and Surface Conditions on Gas/Liquid Two-Phase Flow in Narrow-Channel
Authors: Yoshida Kenji , Sukawa Toru , Hasegawa Tomoya , Kataoka Isao
Published: March 2009

In the present investigation, detailed observations on the flow patterns and measurements for pressure drop characteristics affected by the curvature effect in a micro-channel were carried out. The test channel has a square cross section that has 2.0mm on a side, and the radii of the curvature were 1.0mm and 3.0mm. It was cleared that the pressure fluctuation intensity became larger in the case of the curvature 1.0mm compared with the case of the curvature 3.0mm. Furthermore, in order to investigate the influence of the wall wettabirity, we applied the water repellent channel. In the case of the water repellent micro-channel, the flow pattern tended to easily transit to Annular flow side compared with the normal micro-channel without the water repellent, and we can see a new flow regime like Rivulet flow due to applying water repellent.
Random Model of Water Hammer Pressure and Probability Analysis in Waterpower Station
Authors: Zhu Yongzhong , Zhang Jian , Hu Ming
Published: March 2009

Considering such factors as the original load of turbine, closure time of wicket gate, and water level of reservoir are changeable in the practical operation of waterpower station, they should be regarded as random variables in water hammer analysis. Accordingly, random model of water hammer with random boundary conditions and random initial states is introduced in this paper. And the probability distribution law of each of random variables is concluded. Concerning a single hydraulic system, firstly, random computational formulas for increasing pressures and maximum pressures of water hammer with random variables are deduced. Then theoretical formulas for sensitivity analysis are provided and, with these formulas, sensitivity analysis for water hammer is made. Besides, probability density formulas for increasing pressures and maximum pressures of water hammer are given. And the method of distribution type fitting is introduced to determine the distribution of water hammer pressures. Thereby conclusions are drawn that the distribution of increasing pressures of water hammer in single systems of waterpower station is log-normal type and that of maximum pressures is normal type. Finally, all the methods involved are verified through computational examples.
Direct Numerical Simulation of Turbulent Boundary Layer Downstream of Turbulence-Generating Grid
Authors: Suzuki H. , Nagata K. , Sakai Y. , Hayase T. , Kubo T.
Published: March 2009

The effects of external grid turbulence in a free stream on the turbulent boundary layer are investigated by means of the direct numerical simulation (DNS). A square turbulence-generating grid, on which the velocity components are set to zero, is located upstream of the flat boundary with a nonslip condition. The fractional step method is used to solve the governing equations. The results show that turbulence intensities and Reynolds stress normalized by the inner parameters are significantly suppressed in the log-law region by the external grid turbulence.
Drag Reduction of Bluff Bodies by Surface Control Based on a Force Theory
Authors: Yang Shih-Hao , Chang Chien C. , Chu Chin-Chou , Liao Shi-Hua , Chern R. L.
Published: March 2009

In the present study, we show how drag reduction of a bluff body can be achieved on a rational basis of a force theory. The force theory indicates where is the best location to apply the surface control to minimize the drag on the body. In particular, the method of drag reduction is illustrated for flow around a circular cylinder. It is shown that drag reduction for the circular cylinder can be as efficient as 46.5%.
Experimental and Numerical Approach to Enlargement and Determination of Performance of Primary Sedimentation Basin
Authors: Razmi A. M. , Firoozabadi B.
Published: March 2009

In the present study, the presence of a baffle and its effect on the hydrodynamics of the flow in a primary settling tank has been investigated experimentally by ADV (Acoustic Doppler Velocimeter). On the other hand, the characteristics of this flow field were simulated by an unsteady two-phase finite volume method, and VOF (Volume of Fluid) model; and results were evaluated by the experimental data. The numerical calculation performed by using k–ε RNG model agrees well with experiments. It depicts the ability of this method in predicting the velocity profile and flow structure. In addition, the optimum position of the baffle to achieve the best performance of the tank was determined by applying the above mentioned numerical scheme.
Dispersion Study in a Giant Intracranial Aneurysm Using Computational Fluid Dynamics Techniques
Authors: Pino-Romainville Francisco A. , Nanduri Jagannath R. , Rai Ansaar T. , Celik Ismail B.
Published: March 2009

The formation and growth of intracranial aneurysms is partly attributed to various hemodynamic factors such as shear stress and pressure. This issue is further investigated in the present paper using some new insight gained from passive scalar dispersion in the blood flow. Intracranial aneurysms are best visualized using selective catheter angiogram technique where a contrast agent added to the blood flow is visualized and filmed dynamically. In the current study, the 2D threshold images produced by “3D rotational X-ray angiography technique” are used in an ‘in-house’ program to construct a 3D volumetric grid which is then used to calculate the blood flow through the aneurysm. Dispersion of a fluid material with properties similar to that of the contrast agent is also modeled in the blood flow. Unlike previous studies, we investigated the dispersion of a pulsed scalar to better understand the flow dynamics. Results from a large aneurysm are compared to those for a relative small one to show the effect of geometry. The dispersion and flow patterns show the localization of high stress in stagnation areas, which may be the potential regions for the origin and growth of aneurysms. We also investigated the dependence of flow properties on the initial and boundary conditions to calculate the pressure and the wall shear stress values for a given geometry.
Lattice Boltzmann Simulations of Droplet Formation in a Co-Flowing Microchannel
Authors: Sang Long , Hong Yiping , Wang Fujun
Published: March 2009

Droplet formation in a co-flowing microfluidic device is investigated with the lattice Boltzmann method (LBM). This LBM code was validated with two benchmarks such as Poiseuille flow through a straight duct and Taylor deformation on droplets between two shearing plates. A comparison of experimental droplet formation in a microchannel (Cramer et al, 2004) showed good quantitative agreement with our modeling results. With this code, a large number of simulations were carried out with various inlet flow rate ratios at various Re and various interfacial tensions in the co-flowing microfluidic system. All resulting droplet sizes are discussed quantitatively with the nondimensional parameters, which is helpful for droplet control in different co-flowing devices.
Improvements in Aerodynamic Performance and Noise Due to Low Solidity Cascade Diffuser in a Centrifugal Blower
Authors: Sakaguchi Daisaku , Ishida Masahiro , Murakami Tengen , Hayami Hiroshi , Senoo Yasutoshi , Ueki Hironobu
Published: March 2009

A high efficiency and a wide operating range are required in recent centrifugal compressors and blowers. Low solidity circular cascade diffuser (LSD) was proposed in place of vaned diffuser and channel diffuser for achieving both higher pressure ratio and wider operating range. In the present study, aerodynamic performance and noise characteristics of LSD were investigated changing a radial location of LSD leading-edge. It is known that an interaction occurs between jet-wake flow discharged from the rotating impeller and the LSD leading edge, however jet-wake flow pattern is almost uniformalized until the radial position of R = 1.20 in the vaneless diffuser. Aiming at reducing the noise generated by the interaction mentioned above, the LSD leading edge was moved from RLSD = 1.10 to 1.15 and 1.20 in a centrifugal blower with low specific speed. The frequency spectra of noise were analyzed and the noise due to LSD were discussed from the view point of overall noise, discrete frequency noise and broadband noise. In order to clarify the relationship between the flow field and the noise, flow behavior in the impeller as well as in the diffuser was simulated using a Navier-Stokes solver ANSYS-CFX. According to the present experimental results, about 40% improvement in diffuser performance and about 11% improvement in unstable flow range were achieved in small flow rates by the LSD compared with the vaneless diffuser except for a small deterioration in diffuser performance at the large flow rate. On the other hand, the noise increased clearly in the case of RLSD = 1.10 at the large flow rate and the small flow rates as well. By locating the LSD blade leading edge downstream farther from the impeller exit, a remarkable reduction in overall noise was achieved without deterioration of diffuser performance. It is found that the noise increase due to LSD is mainly dependent on the broadband noise based on the jet-wake flow, the interaction between the reverse flow and the impeller blades results in the discrete frequency noise defined by the frequency of cross product of the rotational speed of the impeller and the number of LSD blade, and a significant reduction in noise is achieved by uniformalization of the jet-wake flow.
Numerical Study of Blood Flow in the Hepatic Portion of the Inferior Vena Cava
Authors: Matsubara M. , Watanabe M. , Watanabe S. , Konishi K. , Yamaguchi S. , Hashizume M.
Published: March 2009

Budd-Chiari syndrome (BCS) is complete or partial occlusion in the hepatic veins and the hepatic portion of the inferior vena cava (IVC). The cause of BCS is not well known yet, however: abnormal vessel wall shear stress caused by blood flow is thought to increase the likelihood of developing BCS. In order to reveal the formation mechanism of BCS, we construct several vessel models of the IVC and hepatic veins from medical images and study the characteristics of the blood flow in the vicinity of the junctions of the hepatic veins with the IVC numerically.
Comparative Assessment of Turbulence Models for Unsteady Turbulent Flow Predictions in Single Rod Channel Configuration
Authors: Das Kaushik , Basu Debashis , Painter Scott , Howard Lane , Green Steve
Published: March 2009

This paper compares different turbulent models for unsteady flow predictions for axial flow in a single rod channel configuration. The numerical analyses are carried out using the Reynolds Averaged Navier Stokes (RANS) equations and three different turbulent models. The predictions are compared with available experimental results. The three models considered in the present work include the RNG (Renormalization group) k-ε model, the realizable k-ε model, and the Reynolds stress model (RSM). With each model, an unsteady approach commonly referred to as URANS (Unsteady Reynolds Averaged Navier Stokes) solution is used. Predicted results are compared with available experimental results. The predicted time-averaged mean velocity and turbulent stresses are in good agreement with the available experimental results. Flow unsteadiness, which is important for determining heat, momentum, and mass transfer in the gap region, is presented through time histories and spectra of flow and turbulent quantities and their influence on the transportation of fluid across the gap is also explored. The effect of inflow unsteadiness on the solution is explored through comparing the flow field for a constant velocity inlet boundary condition as well as time-varying boundary conditions for the RSM model.
Heterogeneous Structure in Dense Gas-Solid Riser Flows
Authors: You Jun , Zhu Chao , Wang Dawei
Published: March 2009

Recent measurements by Electric Capacitance Tomography (ECT) reveal that, under certain operation conditions, the solid concentration distribution in the dense and acceleration regimes of gas-solid riser flows exhibits a strong heterogeneous structure within the same cross-section. This core-annulus-wall heterogeneous structure, significantly different from the commonly-known “core-annulus (wall)” two-zone structure in riser flows, becomes unstable with the increase in solids loading, which eventually leads to the occurrence of choking [1]. In this study, we propose a mechanistic model to investigate the formation mechanism of these interesting heterogeneous structures. Our model simulation shows that the commonly known “core-annulus (wall)” flow structure occurs at low solid loadings and/or high gas velocities whereas the core-annulus-wall flow structure is formed at moderate solids loading and/or at low gas velocities. With a high solids loading at low gas velocity, sever back mixing results in a solid concentration peak formed in the core, which not only causes the flow instability but also possibly triggers the choking. Model simulations are validated by direct comparisons against measurements in solid concentrations as well as pressure drop along the riser, which shows a fairly good agreement.
Evaluation of the Power Output of a Wind Turbine With a Brimmed Diffuser Shroud in Fluctuating Flows
Authors: Gonzalez A. S. Roberto , Ohya Yuji , Karasudani Takashi , Iba Shusaku , Watanabe Kimihiko
Published: March 2009

Fossil fuels have been used extensively all over the world to satisfy energy demands. However, their availability is limited and their negative impact on the environment undeniable. Due to this, the need to develop alternative energy resources was recognized a few decades ago. Among different alternatives that have been developed, wind energy appears as a promising option to be implemented in many parts of the world. Nonetheless, its development and the cost per kW are still higher than that from fossil fuels. The intermittence of its capability to produce energy and the size of the wind power plant (as compared to a coal or nuclear power plant of the same energy output) have not made its implementation easier. In order to make wind energy more competitive and attractive to investors, new energy systems are desired. Specifically, it is desired to have a higher energy output. In this study a brimmed-diffuser shroud was incorporated into a 1 kW wind turbine. The turbine was then evaluated under fluctuating wind conditions. The experiments were conducted at the large boundary wind tunnel of Kyushu University. It is shown that power output increases for a fluctuating flow as opposed to a steady flow. The turbine power output is capable of following the changes in the wind speed accurately in the range of wind speed fluctuations tested. This is shown by correlation analysis and supported by the frequency spectrum. This study is part of a larger research work aimed at evaluating a novel wind turbine design. The current results are very encouraging. Possible wind sites of wind speed average lower than the current minimum accepted values can be exploited by using a turbine like the one evaluated in this work.
Flow Measurement at Partial Flow Rate With LDV Around Rear Rotor of Contra-Rotating Axial Flow Pump
Authors: Yamashita Shuichi , Watanabe Satoshi , Okuma Kusuo , Shirasawa Kyota , Furukawa Akinori
Published: March 2009

An application of contra-rotating rotors, in which a rear rotor is employed in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. The internal flow field of pump should be considered in the design for higher performance and more stable operation. The flow field in contra-rotating axial flow pump was measured with LDV and wall pressure measurements. In the present paper, the experimental results are shown and the flow behaviors would be discussed.
Measurement for Individual Gas-Liquid Two-Phase Flow Rates Based on Stochastic Features of Differential Pressure Fluctuation
Authors: Uchiyama Tomomi , Tominaga Hirokazu , Minemura Kiyoshi
Published: March 2009

This study proposes a measuring method for the individual phase flow rates of gas-liquid two-phase mixtures flowing through a pipe. First, the time-variations for pressure are measured at three points around a vortex generator mounted in the pipe under the known flow rates. Secondly, the stochastic features of the differential pressure fluctuations, such as the mean and the standard deviation, are calculated to construct a database relating the flow rates with the stochastic features. Consequently, if the differential pressure fluctuations are measured under unknown flow rates, the individual phase flow rates are successfully identified from the database. A neural network is employed for the identification. This study also applies the proposed method for the measurement of air-water two-phase flow and discusses the measured results.
Study of High-Pressure Sirocco Fan Using Double Reversal Rotors
Authors: Shigemitsu Toru , Fukutomi Junichiro , Yasunobu Tomohiro
Published: March 2009

A sirocco fan using double reversal rotors in which inner rotor is settled inside the sirocco fan rotor and each rotor rotates in an opposite direction was proposed for the purpose of higher pressure and more compact structure of a sirocco fan. If the high discharge pressure is obtained with the adoption of the double reversal rotors, it could be used for various purposes. Pressure coefficient of a sirocco fan with double reversal rotors is higher than conventional sirocco fan which is 2.5 times of conventional one and the maximum efficiency point of double reversal rotors shifts larger flow rate than a conventional sirocco fan. On the other hand, it was clarified from the flow measurement results that circumferential velocity component at the outlet of outer rotor of double reversal rotors becomes larger than a conventional one. In the present paper, the performance of a conventional sirocco fan and a sirocco fan with double reversal rotors are shown and the internal flow field at the outlet of outer rotor of both cases is clarified. Then, the effect of different kind of double reversal rotors on the performance and internal flow field is investigated and high performance rotor design of it would be discussed.
Investigation of Inner Structure in Magnetic and MR Fluids by Ultrasonic Propagation Velocity
Authors: Motozawa Masaaki , Iizuka Yuta , Sawada Tatsuo
Published: March 2009

When the magnetic field is applied to magnetic or MR fluids, some of inner particles form clustering structure. These clustering structures influence on the ultrasonic propagation velocity in these fluids. We measured precisely the properties of ultrasonic propagation velocity in these fluids subjected to the magnetic field. The measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. Some interesting properties of ultrasonic propagation such as hysteresis and anisotropy are observed. Based on the experimental results, the inner structures of the magnetic or the MR fluids are analyzed experimentally and the application of non-contact inspection in these fluids by ultrasonic techniques is discussed.
Flow Patterns Downstream of a Mechanical Heart Valve During Systole
Authors: Oshkai P. , Haji-Esmaeili F.
Published: March 2009

Digital particle image velocimetry is employed to study turbulent flow through a bileaflet mechanical heart valve during systolic phase of a cardiac cycle. Unsteady vortex shedding from the valve’s leaflets displays distinct characteristic frequencies, depending on the opening angle of each leaflet. Small- and large-scale transverse oscillations of the separated shear layers are studied using global quantitative flow imaging approach. Turbulent flow structures including jet-like regions and shed vortices are characterized in terms of patterns of instantaneous and time-averaged velocity, vorticity, and turbulence statistics.
Dissolution of a Carbon Dioxide Bubble in a Vertical Pipe
Authors: Abe Satoru , Okawa Hideaki , Hosokawa Shigeo , Tomiyama Akio
Published: March 2009

Dissolution of single carbon dioxide (CO2) bubbles in a vertical pipe of 25 mm in diameter are measured to examine the effects of the ratio λ of sphere–volume equivalent bubble diameter d to pipe diameter D, liquid Reynolds number ReL and surfactants on mass transfer. The bubble diameter d and Reynolds number ReL are varied from 5.0 to 26 mm (λ = 0.20 − 1.0) and from 0 to 3100, respectively. Millipore water, tap water and water contaminated with Triton X–100 are used for the liquid phase. Mass transfer coefficients kL are evaluated from changes in d. The kL decreases with increasing λ for bubbles in stagnant millipore water because of the decrease in bubble rising velocity due to the wall effect. Measured Sherwood numbers Sh do not depend on ReL because a turbulent fluctuation velocity in bulk liquid flow is much smaller than a relative velocity between a bubble and liquid. The mass transfer correlation for a bubble in a stagnant liquid proposed by Johnson et al. is applicable to a bubble in pipe flow, provided that a correct relative velocity between a bubble and liquid is substituted in the correlation. Due to the retardation of capillary wave, mass transfer coefficients for bubbles in contaminated water becomes smaller than those in millipore and tap waters.
An Experimental Study of Turbulent Convection in Air Using PIV Technique
Authors: Bukhari Syed J. K. , Siddiqui Kamran
Published: March 2009

Airside turbulent flow structure in a coupled air-water system has been investigated during natural convection. Two-dimensional velocity field in a plane perpendicular to the surface was measured using particle image velocimetry (PIV). The results show the presence of different flow regimes in turbulent velocity fields which increase the complexity of the phenomena. The spectral analysis shows the existence of two power law regimes in the wavenumber spectra of the horizontal and vertical turbulent velocities. The regime at lower wavenumbers exhibits slopes of −3 which correspond to the buoyancy subrange where the energy loss is due to the work against buoyancy. At relatively higher wavenumbers, the inertial subrange with slopes of −5/3 is manifested. The trends of the wavenumber spectra in the present study are similar to the kinetic energy spectra observed in the geophysical studies over land and oceans, which indicates that laboratory experiments could be used to understand the near-surface dynamics in the lower atmosphere.
A Method for Evaluating the PIV Measurement Error in a Centrifugal Pump
Authors: Yang Hua , Tang Fang-Ping , Zhou Ji-Ren , Liu Chao , Yu Li-Hong
Published: March 2009

Based on the equation of the mass conservation, a method of relative error analysis is presented in this paper. The two-dimensional and three-dimensional PIV data in the impeller and volute of the centrifugal pump are evaluated by this method. The maximum relative errors of two-dimensional flow fields in the impeller and volute are 2.85% and 10.50% respectively, which of three-dimensional are 3.41% and 2.59% respectively. It indicates that there is acceptable accuracy of the relative error using two-dimensional PIV to measure the flow fields in the impeller. Axial direction velocity can not be neglected near the outlet of the rotating impeller in the volute and the flow fields must be measured by three-dimensional PIV to obtain the reliable experimental data.
Motion of Single Drops in Linear Shear Flows
Authors: Myint Win , Hosokawa Shigeo , Tomiyama Akio
Published: March 2009

Motions of single silicon oil drops rising in linear shear flows of glycerol-water solutions are measured to investigate the effects of the viscosity ratio κ and dimensionless shear rate Sr on drag forces under the conditions of −6.3 ≤ logM ≤ −4.8, 0.94 ≤ κ7.04, 1 < Re ≤ 23 and 3.2 ≤ ω ≤ 6.0 s−1, where M is the Morton number and ω the magnitude of the velocity gradient of the continuous phase. As a result, we confirmed that (1) the drag coefficient CD of a drop in a linear shear flow takes a higher value than the drag coefficient CD0 of the same-size drop in a stagnant liquid, (2) CD/CD0 increases with Sr, and (3) the augmentation of CD becomes large as κ increases.
Direct Numerical Simulation of Turbulent Mass Transfer Around a Rotating Stepped Cylinder
Authors: Yoon Dong-Hyeog , Yang Kyung-Soo , Bremhorst Klaus
Published: March 2009

Direct Numerical Simulation was carried out to predict mass transfer in turbulent flow around a rotating stepped cylinder. An immersed boundary method was employed for efficient implementation of the irregular cylinder surface on the cylindrical grid system. This investigation is a follow-up study of Nesic et al. [Corrosion, Vol. 56, No. 10, pp. 1005 – 1014] The original motivation of this work stemmed from the efforts to design a simple device which can generate flows of high turbulence intensity at low cost for corrosion researchers. Two cases were considered; Sc = 1 and 10 both at Re = 335. Here, Sc and Re stand for Schmidt number and Reynolds number, respectively, based on the step height and the surface speed of the cylinder upstream of the step. Characteristics of the averaged concentration field are presented and analyzed. Correlation between the wall-shear stress and the mass-transfer rate is also discussed. The numerical results are qualitatively compared with those of experiments conducted with a similar flow configuration.