bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Flow and Axial Thrust Balancing of a Rocket Pump
Authors: Shimura Takashi , Kawasaki Satoshi , Uchiumi Masaharu , Matsui Jun
Published: June 2012

Internal flow of a cryogenic rocket turbopump is rather complicated compared to ordinary pumps. In order to design and predict characteristics of the axial thrust balancing system, analyses of the internal flow system is essential. In the present study, the calculation method for analyzing the internal flow system taking into account effects of boundary layer conditions and angular momentum change in chambers is applied. The characteristic of an axial thrust balancing system, which is comprised of a balance piston and grooves on the stationary wall, was evaluated. Calculated results showed that the system has a wide self-balancing range and is suitable for rocket turbopumps.
Characteristic Study of Pressure Fluctuation in Centrifugal Pump
Authors: Zhang Yuliang , Zhu Zuchao , Cui Baoling , Li Yi
Published: June 2012

In order to reveal the characteristics of pressure fluctuation in centrifugal pump, based on finite volume method, RNG k–ε turbulence model and sliding mesh, the three-dimensional unsteady incompressible viscous flow in a low-specific-speed centrifugal pump is simulated numerically at different flow rates, wherein SIMPLE arithmetic is used to couple pressure and velocity. The calculation region consists of straight suction chamber, impeller and spiral casing. The results show that pressure wave presents periodic sine or cosine regularity in spiral casing, while the characteristic doesn’t appear in suction chamber. In suction chamber, the dominant frequency of pressure fluctuation is equal to rotational frequency of impeller. And in spiral casing, the dominant frequency of pressure fluctuation is equal to the product of rotational frequency of impeller and blade numbers. The dominant frequency of pressure fluctuation for each detection point is constant at any operation conditions. With the augment of operation flow rate, local average pressure in suction chamber will gradually increase, while local average pressure in spiral casing will gradually decrease. The pressure fluctuation at tongue will be more violent as flow rate increases. The pressure fluctuation in spiral volute will gradually decline along rotational direction of impeller.
Strength Calculation Software Development and Finite Element Analysis of Pump Shaft
Authors: Li Wei , Shi Wei-dong , Jiang Xiao-ping , Sang Yi-meng , Li Tong
Published: June 2012

With the wide applications to the fields of petrochemical, military, metallurgy and mining, pumps have to subject to more and more serious working conditions. In order to avoid disaster damage caused by failure of the shaft, it is quite necessary to calculate and examine the shaft strength. A kind of two-dimensional software was developed using the secondary development tool of Object ARX, to achieve the shaft strength calculation accurately and conveniently, and which avoided the disadvantage of the traditional method. The calculation methods of shaft critical rotation speed and the static bending displacement were proposed. Theoretical analysis and calculations on the strength, rigidity, vibration and other aspects of pump shaft were conducted under shut-off condition and best efficiency point using ANSYS APDL software of static, dynamic and transient modal analysis method. The quality of pump shaft was analyzed through the comparisons of numerical results, and further more the accuracy of two-dimensional development software was validated. The practical application indicates that the shaft parts strength calculation software can improve the quality and efficiency, reduce wastage during the pump shaft design. These research achievements will also have a great application prospect.
Experimental and Numerical Analysis of Pressure Pulsations and Mechanical Deformations in a Centrifugal Pump Impeller
Authors: Berten Stefan , Hentschel Sebastian , Kieselbach Karin , Dupont Philippe
Published: June 2012

Deformations, mechanical stresses and vibrations in centrifugal pumps are the result of pressure fluctuations, which are acting as excitation forces. When a pump operates at its optimum, the pressure pulsations are at minimum, but for a pump operating in part-load, pressure pulsations increase and subsequent vibration and deformation levels increase. In a recent experimental research, the pressure pulsations and the resulting structural stresses in the last stage impeller of a multistage pump have experimentally investigated for different operating conditions [1]. The experimental investigations have been complemented by transient numerical simulations using a commercial CFD code and structural analysis using the pressure pulsations resulting from the CFD code as boundary conditions. In the present study, a validation of these CFD and FEM simulations is presented. The analysis has been performed in three steps. In the first step, the transient CFD results for different load cases are analyzed and compared with the experimental results in order to evaluate the CFD simulations. In the second step the time domain pressure pulsation data are post-treated and decomposed into a series of rotating pressure waves. These pressure waves are then applied as boundary conditions to an FEM model and one full impeller revolution is simulated as steady calculations for 72 angular positions. The pressure pulsations in the best efficiency point are regularly distributed in space and time and dominated by rotor-stator-interaction. For part-load operation, the pressure distribution becomes more and more unsteady. The CFD results for part load exhibit stationary stall in the diffuser for a flow rate relative to best efficiency point of q* = 0.9 and unsteady stall behavior for a q* = 0.8. While the numerical CFD results agree well with experimental data for q* = 1 and q* = 0.9, at lower part load (q* = 0.8) the CFD didn’t reproduce the experimentally observed flow behavior, especially the rotating stall. The FEM results at design conditions show relatively low tangential stresses at the impeller outlet, which agree well with the measured deformations and stresses.
Transient Behavior of a Radial Vaneless Diffuser
Authors: Dazin Antoine , Dupont Patrick , Caignaert Guy , Bois Ge´rard
Published: June 2012

The paper refers to the behavior of a radial flow pump vaneless diffuser during a starting period. Results obtained with a 1D numerical model are compared with some new experimental data which have been obtained using 2D/3C High repetition rate PIV within the diffuser coupled with unsteady pressure measurements. These tests have been performed on a test rig with a radial impeller matched with a vaneless diffuser. They have been made in air, on a test rig well adapted for studies on interactions between impeller and diffuser, as well as for the use of optical methods and especially Particle Image Velocimetry (PIV) as there is no volute downstream of the diffuser. The present study refers to new experiments combining pressure measurements and 2D/3C High Speed PIV at partial flow rates within a vaneless diffuser with a large outlet radius. Four Bru¨el & Kjaer condenser microphones are used for the unsteady pressure measurements. They were flush mounted on the shroud side of the diffuser wall and on the suction pipe of the pump. The sampling frequency was 2048 Hz. For PIV measurements, the laser sheet was generated by a Darwin PIV ND:YLF Laser at three heights within the diffuser. PIV snapshots have been recorded by two identical CMOS cameras. A home made software has been used for the images treatment. The results consist in fields of 80 × 120 mm2 and 81 × 125 velocity vectors with a temporal resolution of 250 velocity maps per second. For each flow rate and each laser sheet height in the diffuser, two acquisitions of about 1500 velocity maps have been realised. The experimental data are compared with the ones provided by a 1D transient model of the flow within the diffuser.
Experimental Study on Cavitating Flow in Impeller of Axial-Flow Pump
Authors: Li Zhong , Yang Minguan , Kang Can , Gao Bo , Ji Kai
Published: June 2012

Based on the external characteristic test, the performance of designed axial-flow model pump was determined. The cavitation performance of model pump at the best efficiency point was confirmed through the cavitation test. The cavitating flows in impeller at different NPSH values were shot by the high speed digital camera. MiVnt image analysis software was utilized to process the shooting images, track the cavitation region and outline of cavitation bubbles cluster. The experimental results show that the incipient cavitation regions are located in the inlet of blade suction surface near the tip and the leading edge of tip airfoil. With the decrease of NPSH values, the cavitation region at tip airfoil moves gradually from leading edge to trailing edge and the type of cavitation is vortex cavitation, its rotation axis direction is the same as circumferential direction. The cavitation region at blade suction surface indicates the same moving trend as at tip airfoil. The emerging of cloudy cavitation at the middle of blade suction surface indicates the beginning of pump cavitation. With the further increase of volume proportion of cavitation bubbles in impeller channel, the pump performance decreases severally. The experimental results reveal the preliminary laws of cavitating flow and provide an effective reference for the cavitation region and development process in impeller of axial-flow pump.
Numerical Determination of the Acoustic Impedance of a Centrifugal Pump
Authors: Barrio Rau´l , Blanco Eduardo , Keller Jens , Parrondo Jorge , Ferna´ndez Joaqui´n
Published: June 2012

The perturbations generated at the blade-passing frequency and higher harmonics in centrifugal pumps due to the rotor-stator interaction represent a significant contribution to the total load on the machine, which can bring about excessive vibration and noise levels thus limiting the pump performance. These perturbations are in close relation to the pump’s internal geometry and also to the point of operation; in addition, their magnitude is influenced by the acoustic coupling between the pump and the pipelines. The latter can be characterized by the equivalent acoustic impedance; however, the acoustic characterization of the pump is more complex. The usual boundary conditions imposed in numerical simulations of centrifugal pumps (constant outlet velocity, constant static pressure, or pressure loss proportional to squared velocity) induce a particular type of coupling between the pump and the hydraulic network. Hence, the real performance values of the pump are expected to change from those obtained in the simulations if the coupling conditions are modified. The purpose of the present investigation is to obtain a simple 1-D model for the acoustic impedance of a volute-type centrifugal pump from the full 3-D unsteady flow simulations carried out with the code Fluent®. For this purpose, a specific pressure fluctuation is imposed at the outlet port of the pump by means of a user-defined function. The amplitude and frequency of this fluctuation is modified to obtain the response of the pump (i.e., the acoustic impedance) for a series of flow rates. The acoustic 1-D model obtained will allow a quick prediction of the perturbations generated from the acoustic impedance of the network to which the pump is to be coupled.
Application of Automated Optimisation to Pump Impeller Design
Authors: Krueger Susanne , Maurer Wolfgang
Published: June 2012

Dominating factors in today’s pump design process are reducing time to market and increasing demands on product flexibility. With these requirements, an adaptation of the pump design process is crucial and the need for an optimisation environment is only one part. In this paper we present our semi-automated impeller design process and its integration into a fully automated optimisation environment. The setup of the workflow for both approaches including impeller design tool, mesh generation, CFD analysis, and the steering tool are described. The optimisation process starting from a set of basic designs (Designs of Experiments, DOE) over the proper optimisation to the design analysis is explained by means of a suction impeller with opposing objectives like maximising hydraulic efficiency and minimising NPSH3% values yielding different geometry solutions all being a compromise. During this process, performance values for duty point, partload and overload are evaluated by CFD. An overall efficiency parameter is defined representing the averaged efficiency of these three operating points. Suction performance can be handled differently and evaluated only for different operating points and treated either as objectives or constraints. The approach developed in this paper is finally applied for two test cases. The first example describes the design of a suction impeller which has to fit into an existing casing and limits us to the modification of the blade shape only. Objectives are overall and duty point efficiency, NPSH3% at duty point is handled as a constraint. The overall efficiency objective requires a high plateau-like efficiency from partload to overload operating condition. The classical way of an optimisation is starting with a DOE, followed by an optimisation, visualisation of the Pareto Frontier and selection of the final design. The second example requires the replacement of a suction impeller which is supposed to operate cavitation free at site conditions. Main objectives are the reduction of NPSHInc and increase of partload efficiency while maintaining NPSH3% and overall efficiency. Limitations in development time forces us to go a different way in the design process. We start with a general exploration of the parameter range and study the parameter influence on the objectives and complete the process with an optimisation for a very limited number of blade parameters to obtain the objectives.
Industry-University Collaborative Project on Numerical Predictions of Cavitating Flows in Hydraulic Machinery: Part 1—Benchmark Test on Cavitating Hydrofoils
Authors: Kato Chisachi
Published: June 2012

Through an industry-university collaborative project, extensive benchmark studies have been made for numerical prediction of cavitating flows around two-dimensional Hydrofoils: Clark-Y 11.7% and NACA0015. The emphases are placed on the ability of present cavitation models to predict the breakdown characteristics for these hydrofoils. The benchmarking was done for a light and a moderate loading condition of these hydrofoils at a chord-based Reynolds number in the order of 106. Four commercial CFD flow solvers, ANSYS CFX, ANSYS Fluent, and STAR-CCM+, and SCRYU/Tetra, along with four open-source or in-house flow solvers in universities participated in this benchmark. All the cavitation models, except one, implemented in these flow solvers are based on an assumption of homogenous media of one fluid, for which inception, growth, decay and destruction of cavitation are expressed by density change of the mixture fluid composed of liquid and gas phases. They differ with each other in how they determine the mixture fluid density and can be categorized into of barotropic type or of source-sink type. Despites these differences in the cavitation models themselves and differences in the Navier-Stokes solvers, turbulence models and computational grids, the results of the benchmark show a consistent trend of discrepancy between the predicted and measured breakdown characteristics. Namely, none of the cavitation models is able to predict sudden drop of the lift coefficient near the breakdown point confirmed in the measured characteristics. The lift coefficients predicted by all the cavitation models show a gradual decrease with decreasing cavitation number. This discrepancy between the predicted and measured breakdown characteristics is most prominent at the higher loading condition for NACA0015. But, it is consistently confirmed for the other cases investigated in this benchmark. The difference seems to be the results of under prediction of the cavity length, which probably comes from an intrinsic limitation associated with a cavitation model based on an assumption of homogeneous media of one fluid.
Fluid-Induced Forces in Pump Liquid Seals With Large Aspect Ratio
Authors: Untaroiu Alexandrina , Hayrapetian Vahe , Untaroiu Costin D. , Allaire Paul E. , Wood Houston G. , Schiavello Bruno , McGuire James
Published: June 2012

The instability due to fluid flow in seals is a known phenomenon that can occur in pumps and compressors as well as in steam turbines. Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). Unlike the bulk flow models, computational fluid dynamics (CFD) makes no simplifying assumption on the seal geometry, shear stress at the wall, relationship between wall shear stress and mean fluid velocity, or characterization of interfaces between control volumes through empirical friction factors. This paper presents a method to calculate the linearized rotor-dynamic coefficients for a liquid seal with large aspect ratio (balance drum) subjected to incompressible turbulent flow by means of a three dimensional CFD analysis to calculate the fluid-induced forces acting on the rotor. The Reynolds-averaged Navier-Stokes equations for fluid flow are solved by dividing the volume of fluid into a discrete number of points at which unknown variables are computed. As a result, all the details of the flow field, including the fluid forces with potential destabilizing effects, are calculated. A 2nd order curve fit is then used to express the fluid-induced forces in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients.
Performance and Flow Condition of Cross-Flow Wind Turbine With a Symmetrical Casing
Authors: Fukutomi Junichiro , Shigemitsu Toru , Toyohara Masaaki
Published: June 2012

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio. Therefore, it is a good candidate for use as a self-starting turbine. Furthermore, it has low noise and excellent stability; therefore, it has attracted attention from the viewpoint of applications as a small wind turbine for an urban district. However, its maximum power coefficient is extremely low (10%) as compared to that of other small wind turbines. In order to improve the performance and the flow condition of the cross-flow rotor, symmetrical casing with a nozzle and a diffuser are proposed and experimental research with the symmetrical casing is conducted. The maximum power coefficient is obtained as Cpmax = 0.17 for casing and Cpmax = 0.098 in the case without the casing. In the present study, power characteristics of the cross-flow rotor and those of the symmetrical casing with the nozzle and the diffuser are investigated. Then, the performance and internal flow patterns of the cross-flow wind turbine with the symmetrical casings are clarified. After that, the effect of the side boards set on the symmetrical casing is discussed on the basis of the analysis results.
Experimental Investigation of Helical Cross-Flow Axis Hydrokinetic Turbines, Including Effects of Waves and Turbulence
Authors: Bachant Peter , Wosnik Martin
Published: June 2012

The performance characteristics of two cross-flow axis hydrokinetic turbines were evaluated in UNH’s tow and wave tank. A 1m diameter, 1.25m (nominal) height three-bladed Gorlov Helical Turbine (GHT) and a 1m diameter, four-bladed spherical-helical turbine (LST), both manufactured by Lucid Energy Technologies, LLP were tested at tow speeds up to 1.5 m/s. Relationships between tip speed ratio, solidity, power coefficient (Cp), kinetic exergy efficiency, and overall streamwise drag coefficient (Cd) are explored. As expected, the spherical-helical turbine is less effective at converting available kinetic energy in a relatively low blockage, free-surface flow. The GHT was then towed in waves to investigate the effects of a periodically unsteady inflow, and an increase in performance was observed along with an increase in minimum tip speed ratio at which power can be extracted. Regarding effects of turbulence, it was previously documented that an increase in free-stream homogenous isotropic turbulence increased static stall angles for airfoils. This phenomenon was first qualitatively investigated on a smaller scale with a NACA0012 hydrofoil in a UNH water tunnel, using an upstream grid turbulence generator and using high frame-rate PIV to measure the flow field. Since the angle of attack for a cross-flow axis turbine blade oscillates with higher amplitude as tip speed ratio decreases, any delay of stall should allow power extraction at lower tip speed ratios. This hypothesis was tested experimentally on a larger scale in the tow tank by creating grid turbulence upstream of the turbine. It is shown that the range of operable tip speed ratios is slightly expanded, with a possible improvement of power coefficient at lower tip speed ratios. Drag coefficients at higher tip speed ratios seem to increase more rapidly than in the non-turbulent case.
Numerical Investigation on Channel Vortex in a Francis Turbine
Authors: Zhang Maojin , Liu Shuhong , Wu Yulin , Liu Demin , Zhang Lefu
Published: June 2012

When a Francis hydraulic turbine operates under different working heads at small flow condition, the fluid in the flow passage will generate vortex shedding near the blade leading-edge and form the channel vortex in the blade passages due to the mismatch between the outlet angle of guide vane and the inlet angle of runner blade. The severity of channel vortex will trigger high-frequency vibration or generate unit resonant vibration, affecting the operational stability of the turbines. In this paper some typical operation points were chosen out for the steady simulation of a model turbine according to a unit hill-chart. The computational domain was chosen as the whole flow passage from the inlet of the volute to the outlet of the draft tube. Based on RNG k–ε turbulence model, the internal flows was simulated, and the occurrence of vortex between the turbine runner blades was discussed. The numerical results show that the vortex motion near the development-line (IVDL) is stronger than that near the channel vortex inception-line (IVIL) in channel vortex zone marked in the hill-chart. The velocity triangle is used to explain the reasons that channel vortex occur in the suction side at high working head while in the pressure side at the low working head, and two different forms and formation mechanism of the channel vortex were analyzed.
Counter-Rotating Type Hydroelectric Unit (Effects of Blade Numbers on On-Cam Operations)
Authors: Suzuki Toshiaki , Takano Gohki , Nakamura Yoshihiro , Kanemoto Toshiaki
Published: June 2012

To cope with warming global environments, authors have proposed the counter-rotating type hydroelectric unit, which is composed of tandem runners and the peculiar generator with double rotational armatures. The unit can be provided for various water circumstances at not only the onshore but also the offshore. This paper discusses effects of setting angle and the number of runner blades on turbine performances and then optimum blade setting angles giving the maximum output and/or the maximum efficiency, namely the on-cam operation, are presented at various discharges/heads.
Diesel Engine Performance With Variable Operating Parameter by Using Waste Plastic Disposal Fuel
Authors: Sudrajad Agung , Hirotsugu Fujita , Ali Ismail , Hamdan Mohd Hazmie
Published: June 2012

Optimization of using waste plastic fuel on diesel engine was observed. The investigation experimental project was comparison between using waste plastic fuel and diesel fuel. The engine experiment was conducted with YANMAR TF120 single cylinder four stroke diesel engine set-up at variable engine speed at 2100, 1900, 1700, 1500 and 1300 rpm. The data have been taken at each point of engine speed during the stabilized engine-operating regime. Measurement of emissions parameters at different engine speed conditions have generally indicated reduce in engine CO2, NOx and SOx emission when using plastic fuel compared to base diesel oil with good in fuel consumption.
Investigation of Rod Vibrations in Droplet Two-Phase Flows
Authors: Komuro Yoshiteru , Kawara Zensaku , Kunugi Tomoaki
Published: June 2012

Flow-induced vibrations are important problems in nuclear power plants from the view point of reactor safety. In the investigations of these vibrations especially those induced by two-phase flows, a numerical simulation plays a significant role, so it is necessary to obtain the experimental datasets that can validate the results of the numerical simulation. This paper deals with the experimental data of one-end-supported rod vibration, and focuses on the differences between the rod vibrations induced by single-phase air flows and those induced by droplet two-phase flows. In the experiments, the displacement of the non-supported end of the test rod was visualized by the high speed camera with high spatial and temporal resolutions, namely 9.5 μm and 500 μsec. Using an image analyzing software, the rod vibration displacements were measured by the motion tracking method. The curved surface of the rod was observed by another high speed camera and the relationship between the rod vibrations and the wet condition on the surface of the rod was investigated. In addition, the vibrations measured by the strain gages and those by the high speed camera were compared to discuss the differences in these two ways of the measurements.
Pressure Correction Method for Simulating Solid-Fluid Mixture Flow
Authors: Lin San-Yih , Chin Ya-Hsien , Chen Yi-Cheng
Published: June 2012

A pressure correction method is developed to simulate fluid-particle interaction flows. In this Paper, the three-dimensional solid-fluid mixture flows are investigated. The pressure corrected method coupled with the direct-forcing immersed boundary (IB) and the volume of fluid (VOF) methods is used to simulate the mixture flows. A discrete element method (DEM) together with a multi-time-step algorithm is introduced into the pressure correction method to calculate the forces and torques between solid bodies and between solid bodies and walls. As a demonstration of the efficient and capabilities of the present method, four test cases are simulated. They include sedimentation of one spherical particle in an enclosure, collapse of six solid-cylinder layers, two-dimensional solid-fluid mixture flow, and three-dimensional solid-fluid mixture flow.
Effect of Helical Strakes Around a Finned Tube on Aeolian Tone
Authors: Hamakawa Hiromitsu , Ito Yuki , Kamo Ryunosuke , Nishida Eiichi
Published: June 2012

In the present paper, the characteristics of vortex shedding and Aeolian tone radiated from a finned tube with helical strakes were experimentally investigated. The helical strakes are mounted spirally around a serrated finned tube surface. We measured the turbulence intensity in the wake, velocity fluctuation spectrum, the coherence of velocity fluctuations in the spanwise direction and SPL spectrum. The Aeolian tone radiated from the finned tube with helical strakes at high Reynolds number was smaller than the case of no helical strakes. The helical stakes were effective to reduce the Aeolian tone radiated from the finned tube. And the existence of helical strakes of large diameter caused the decrease of the periodicity and the turbulence intensity in the wake of the finned tube. The coherent scale of Karman vortex in the spanwise direction is smaller than that of a finned tube without helical strakes. However, the effect of helical strakes of small diameter on vortex shedding depended on the Reynolds number. The Karman vortex was clearly formed even in the case of helical strakes of small diameter at low Reynolds number. The existence of helical strakes of small diameter around a finned tube caused the increase of the periodicity of vortex shedding from a finned tube. The coherent scale of Karman vortex in the spanwise direction was larger than that of a finned tube without helical strakes.
Fluid-Structure Interaction of Circular Cylinders With Elastic Surface
Authors: Sharify Esmatullah Maiwand , Arai Norio , Takahashi Shun
Published: June 2012

This contribution presents the numerical study of Fluid Structure Interaction (FSI) problems and discusses the oscillatory characteristics of the elastic bodies and flowfield around circular cylinders. This paper deals with the motion of the elastic body and the flowfield using computational fluid dynamics (CFD) in two-dimensional and three-dimensional simulations. The governing equations are the continuity equation and incompressible Navier-Stokes equations. These equations are solved by MAC (Marker and cell) method by using Poisson equation for pressure component and momentum equations for velocity components. The convective terms of momentum equations are discretized by the third-order upwind Kawamura-Kuwahara scheme. All of the discretized equations are solved by the Successive over-relaxation (SOR) method. The equation of motion consists of mass-spring-damper system and it is solved by the 4th order Runge-Kutta method. The objective is to investigate the influence of the elastic surfaces with respect to the vibration characteristics of cylinders in unsteady flows. As a result, it is obtained that due to passive deformation of elastic surface for single cylinder the drag coefficient increases in both 2D and 3D cases. It is noticed that the effect of elastic surface in 2D case is stronger compared to 3D case. In the case of double cylinders, the elastic surface affects on vibration characteristics of upstream and downstream cylinders, and it is significant on downstream cylinder.
Three-Dimensional Measurement of Interaction Between a Circular Cylinder and Surrounding Flow by Digital Holographic Particle Tracking Velocimetry
Authors: Tanaka Yohsuke , Murata Shigeru
Published: June 2012

As an example of Flow-Induced Vibration (FIV), an interaction between a circular cylinder and a surrounding flow is measured by Digital Holographic Particle Tracking Velocimetry (DH PTV). Tracer particles having two different diameters are dispersed in a cylinder and pipe flow. The cylinder, containing dispersed tracer particles, is made of an acrylic transparent resin and is attached to an inner wall of the pipe. In order to suppress a difference in the refractive index between the cylinder and fluid, the acrylic pipe is filled with a refractive-index-matching liquid having the same refractive index as the cylinder (1.49). The holographic pattern of the tracer particles dispersed in both the cylinder and fluid is measured by digital in-line holography. The three-dimensional position of particles is detected by reconstructed holographic patterns at each time step. Three-dimensional velocity of a surrounding flow and three-dimensional vibration of the cylinder are derived by using a Self-Organizing Map (SOM). Vector fields for the vibrating cylinder and surrounding flow are individually identified from the difference in the particle size detected by digital holography.
Time Resolved Measurements of the Pressure Field Generated by Vortex-Corner Interactions in a Cavity Shear Layer
Authors: Liu Xiaofeng , Katz Joseph
Published: June 2012

A 2D open cavity shear layer flow, especially its interaction with the trailing corner of the cavity, is investigated experimentally in a water tunnel, at a Reynolds number of 4.0×104, based on cavity length. Time-resolved PIV, at an image sampling rate of 4500 fps is used to simultaneously measure the instantaneous velocity, material acceleration and pressure distribution. The pressure is obtained by spatially integrating the material acceleration (Liu and Katz [19]). A large database of instantaneous realizations enables detailed visualization of the dynamic changes to the shear layer vortices, including convection, deformation and breakup as they impinge on the cavity trailing corner, as well as their interactions with the freshly generated boundary layer around the corner walls. The vorticity on top of the corner is originated from advected shear layer vortices and locally generated vorticity associated with the local pressure gradients. The resulting periodic recirculating flow above the corner generates the lowest mean pressure in the entire flow field. Two mechanisms with distinct characteristic frequencies affect the periodic variations in vorticity and pressure around the corner. The first is caused by streamwise transport of the large shear layer vortices. For example, when these vortices are located just upstream of the corner, they induce a downwash, which periodically eliminates the recirculating flow there. This recirculation and the associated low pressure reappear after the vortex climbs over the corner. The second mechanism involves low frequency undulations of the entire shear layer, which affect its interaction with the corner, and causes substantial variations in the pressure maximum along the vertical wall of the corner, and pressure minimum above it. These undulations are self sustained since the corner pressure fluctuations alter the recirculation speed in the cavity, which in turn change the shear layer elevation during initial rollup, and even modify the boundary layer upstream of the cavity. The time resolved pressure distribution can also be used for estimating the dipole noise radiated from the corner. The characteristic frequencies of the hydraulic and acoustic fields can be traced back to specific flow phenomena. Analysis shows that the unsteady surface pressure along the vertical wall of the trailing corner is a major dominant source of low frequency noise.
Vortex Structure Rolled Up From Elastic Thin Film by Fluid Structure Interaction Simulation
Authors: Nagata Tetsushi , Fuchiwaki Masaki , Tanaka Kazuhiro
Published: June 2012

The flow field around a moving body is treated as a fluid-structure interaction (FSI), which is a series of phenomena from the elastic deformation of a body to vortex generation/growing/development. In the present paper, we simulate the fluid structure interaction of a flow field around an elastic heaving thin film with large deformation using ANSYS 12.1/ANSYS-CFX 12.1, and clarify the elastic deformation, velocity, acceleration, vortex roll-up from the trailing edge, circulation, and dynamic lift, as well as other important parameters to obtain the vorticities, circulations and dynamic lifts. The elastic deformation, velocity and acceleration can produce the large vorticity and the circulation. In particular, the vorticity that rolled up from the trailing edge of the thin film is dependent on the elastic velocity, and the vorticity production at the trailing edge is dependent on the elastic acceleration. Moreover, the vortex production is also distributed to the circulation production and the dynamic lift. Therefore, the elastic deformation, velocity and acceleration can produce and change the flow field for the vorticity, circulation, and dynamic force.
Torque Converter Stress Analysis by Transient FSI Technique
Authors: Yamaguchi Takeshi , Okumura Akihiko
Published: June 2012

The performance of a torque converter has been one of the most important areas of improvement for an automatic-transmission equipped automobile. Improving the torque converter’s performance and efficiency is key to saving fuel consumption, which is an important consideration with recent environmental awareness. Moreover, improving the overall automobile performance has led to more compact and lightweight transmissions. With the growing space constraints, the evolution of the torque converter has been towards smaller and more elliptical shapes. Since the smaller blades within the torque converter still have to endure the same engine torque, more strength is required of each blade of the pump, the turbine and the stator. There has been much research carried out to predict hydrodynamic performance and to understand the flow field inside a torque converter either experimentally or analytically using Computational Fluid Dynamics (CFD). However, none of the research has focused on the strength of the torque converter components — the blade, the shell and the core. The previous method for evaluating the blade strength had been to apply a simple, centrifugal pressure load on the blade using Finite Element Analysis (FEA). This method is no longer adequate for predicting blade stress since the pressure distribution on the blade is now known from CFD results. In this work, the fluid-structure interaction (FSI) technique is used to determine the deformation, which is indicative of the stress level of the blade, the shell and the core. In addition, this research compares the computational results from a model containing all blades to a conventional model of a single blade with axial symmetry. Analysis of the model containing all blades shows a completely different deformation mode than the single-blade model, especially for the pump blade. The differing results suggest that using a single-blade model analysis is less accurate for examining the torque converter structure.
Fluid-Structure Interaction for Flutter Predictions in Transonic and Supersonic Flows
Authors: Yang Zhi , Zhao Xiang , Zhang Sijun , Chen Chien-Pin
Published: June 2012

This paper describes a numerical methodology coupling Euler/Navier-Stokes equations and structural modal equations for predicting flutter in transonic and supersonic flows. This coupling between Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) is achieved through a Multi-Disciplinary Computing Environment (MDICE), which allows several computer codes or ‘modules’ to communicate in a highly efficient fashion. The present approach offers the advantage of utilizing well-established single-disciplinary codes in a multi-disciplinary framework. The flow solver is density-based for modeling compressible, turbulent flow problems using structured and/or unstructured grids. A modal approach is employed for the structural response. Two benchmark cases are employed to validate the present method. Flutter predictions in subsonic flows for an AGARD 445.6 wing at different Mach numbers (0.499 to 1.141) are presented and compared with experimental data. Supersonic plate flutter with Mach number range between 1.8 and 3.2 is studied and the critical Mach number is computed, our results are in a good agreement with the analytical solutions.
Experimental and Computational Aeroelastic Analysis of a Composite Material Delta Wing in Low Subsonic Flow
Authors: Sapkal Kedar , Attar Peter J.
Published: June 2012

An experimental and computational study of the flutter and limit cycle oscillations (LCOs) of a three layer, carbon fiber composite material 45° delta wing is presented. The computational aeroelastic model utilizes a set of nonlinear structural dynamics (modal) equations which are coupled to a vortex lattice aerodynamic model. The nonlinear modal equations for the structure are formulated using a system identification methodology. To reduce the computational time needed in the computation of the strain energy needed to construct the reduced order structural dynamics model, a new algorithm which uses a Smolyak sparse grid technique is proposed to perform the sampling of strain energy data used for generation of the equations of motion. Experiments and computations are performed, and compared, for a number of layup configuration angles. The qualitative agreement between experimental flutter and limit cycle results is good with both sets of results displaying similar trends with respect to variations in layup angle and a non-dimensional parameter which gives a measure of the bending-torsion coupling in the laminate.
Direct Simulations of Incipient Erosion of Solid Particle Beds due to Shear Flow
Authors: Derksen Jos
Published: June 2012

Direct numerical simulations of the shear flow over assemblies of uniformly sized solid spheres have been performed using the lattice-Boltzmann method. First non-moving spheres are considered; the random sphere assemblies comprise monolayers, double layers, and triple layers. Then situations with moving spheres were simulated, directly resolving granular bed erosion. The Reynolds numbers based on the sphere radius and the overall shear rates were smaller than one. For the fixed spheres the results were interpreted in terms of the drag force (the force in streamwise direction) and lift force (the force in wall-normal direction) experienced by the spheres as a function of the denseness of the bed and the depth of the spheres in the bed. For the moving spheres the onset of erosion as a function of the Shields number was studied, with results that were in accordance with experimental data.
Solid Fluctuations and Dispersion in Liquid-Solid Fluidized Beds With Low Surface Tension Media
Authors: Lim H. O. , Seo M. J. , Kang Y. , Jun K. W.
Published: June 2012

Fluctuations and dispersion of solid particles were investigated in a liquid-solid fluidized bed of which diameter was 0.102 m and 2.5 m in height. Effects of liquid velocity (0.005 ∼ 0.13 m/s), particle size (0.5 ∼ 3.0 × 10−3 m) and surface tension of continuous liquid media (56 ∼ 72 × 10−3 N/m) on the fluctuation frequency and dispersion coefficient of fluidized solid particles were determined. The fluctuating frequency and dispersion coefficient of particles were estimated by means of the relaxation model based on the stochastic theory. Both of fluctuating frequency and dispersion coefficient of particles showed maximum values with a variation of liquid velocity and increased with an increase in the particle size or surface tension of liquid media. The values of fluctuating frequency and dispersion coefficient of fluidized solid particles were well correlated in terms of dimensionless groups as well as operating variables.
Formation of Sedimentary Ripples in a Cylindrical Rotating Tank
Authors: Cui Yan , Wells John C.
Published: June 2012

Experiments on sedimentary ripples in rotating cylinders have been considered as a convenient configuration for studying ripples. This system is simple and convenient to study sediment transport compared to the traditional channel experiments. In the present contribution, we conduct a small scale experiment as a “benchmark” of our numerical model. Processes of pattern formations have been produced and the results of the spiral arm properties are compared to the published experimental data.
Orbits of Small Spherical Tracers in Monodisperse Particle Beds Liquid-Versus Air-Filled Rotating Tumblers
Authors: Wells John C. , Nguyen Tuyen T. B. , Nguyen Anh V.
Published: June 2012

Sorting of particles of different sizes strongly affects the dynamics of river beds. As a model for the sorting of fine particles on the lee face of an alluvial “dune”, we study the orbits of small spherical tracers in monodisperse particle beds in quasi-two dimensional rotating tumblers, both liquid- and air-filled. In addition to searching for clues on lee-face sorting, another purpose is to provide benchmark data for small-scale “qDNS” of bedload sediment transport. While sorting of fines in a rotating tumbler, and other canonical grain flows, has been studied in air, there is a dearth of corresponding studies in liquid. Compared to the “dry” case, our data show that immersion in liquid yields significant differences in bead trajectories at matched Froude number, in the intermittent avalanching regime at low rotation rate.
Development of a Lagrangian-Lagrangian Coupling Method in Solid-Liquid Flows Involving Free Surface
Authors: Yamada Y. , Sakai M. , Mizutani S. , Koshizuka S. , Nonoue T. , Takahashi K.
Published: June 2012

In the industrial area, handling solid-liquid multiphase flows involving free surface is one of the most important problems. However, numerical studies on these complex flows have not been done so far. In this study, we develop a new method to simulate the solid-liquid flows with high viscosity. Lagrangian approaches were employed in the liquid and solid coupling method. Numerical simulations were performed to show the adequacy of this model.
Motion of Descending Solid Particles and Local Flow Around the Particles in Downward Turbulent Water Duct Flow (Keynote)
Authors: Hagiwara Yoshimichi , Fujii Hideto , Sakurai Katsutoshi , Kuroda Takashi , Kitagawa Atsuhide
Published: June 2012

The Stokes number, the ratio of the particle time scale to flow time scale, is a promising quantity for estimating changes in statistics of turbulence due to particles. First, we explored the Stokes numbers in some recent studies. Secondly, we discussed the results of our direct numerical simulation for turbulent flow with a high-density particle in a vertical duct. In the discussion, we defined the particle Reynolds number from the mean fluid velocity in the near-particle region at any time. We evaluated a new local Stokes number for the particle. It is found that the Stokes number is effective for the prediction of the distance between the particle center and one wall. Finally, we carried out experiments for turbulent water flow with aluminum balls of 1 mm in diameter in a vertical channel. The motions of aluminum balls and tracer particles in the flow were captured with a high-speed video camera. We found that the experimental results for the time changes in the wall-normal distance of the ball and the particle Reynolds number for the ball are similar to the predicted results.
Study on Droplet Formation With Surface Tension for Electrohydrodynamic Inkjet Nozzle
Authors: Lee Soo-Hong , Hung Nguyen Xuan , Ko Han Seo
Published: June 2012

Droplet ejection from an Electrohydrodynamic (EHD) inkjet nozzle depends on many factors such as an onset voltage, liquid conductivity, surface tension, etc. Since the surface tension has an influence on the contact angle between the nozzle surface and the liquid droplet, the surface tension change should be investigated for the control of the droplet ejection. In this study, surfactant which can weaken the surface tension force was used to analyze the effect of the surface tension. Furthermore, hydrophobic coating of the nozzle surface was considered as another factor for the droplet ejection. Also, a flow visualization technique was developed to observe the droplet formation and ejection from the EHD inkjet nozzle by various surface tension values.
Combined Numerical and Experimental Study on Drag Torque in a Wet Clutch
Authors: Takagi Youhei , Okano Yasunori , Miyagawa Masatoshi , Katayama Nobuyuki
Published: June 2012

The effect of flow field on drag torque in a wet clutch was examined through a combined numerical and experimental study. Three-dimensional hydrodynamic numerical simulations were carried out, and the drag torque was measured experimentally for a single wet clutch pack. Two-phase flow induced by aeration was visualized in the experiment. In the present drag torque test, the main section was consisted of two parallel circular plates. The plate with the frictional material was rotated. The frictional material was divided into some sections, and radial or circumferential grooves were made on the rotating disk. Automatic Transmission Fluid (ATF) was supplied from the axial center, and ejected into the surrounding open boundary. At low rotation speeds, it was found that the oil flow is of single-phase, and the drag torque is linearly proportional to the rotation speed since the shear stress on the clutch plate increased monotonically. In the single-flow regime, the slope of drag torque curve was controlled with the clearance between the clutch plates. The drag torque reached a peak value at a certain rotation speed, and it decreased gradually after the peak. These observed phenomena were due to the aeration from the inner gap on the disk, and the bubble volume fraction was directly related to the drag torque. The peak of drag torque was controlled by both the flow rate of supplied ATF and the arrangement of grooves on the frictional material. It also was found that the smooth ejection of ATF and the enhancement of aeration led to a reduction in the drag torque.