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Combined Effects of Centrifugal and Coriolis Instability of the Flow through a Rotating Curved Duct with Rectangular Cross Section

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Open Journal of Fluid Dynamics 2014年第1期4卷 1-14页

作者： Rabindra Nath Mondal Samir Chandra Ray shinichiro yanase Department of Mathematics Bangabandhu Sheikh Mujibur Rahman Science and Technology University Gopalganj Bangladesh Department of Mathematics Jagannath University Dhaka Bangladesh Department of Mechanical and System Engineering Faculty of Engineering Okayama University Okayama Japan

Combined effects of centrifugal and coriolis instability of the flow through a rotating curved duct with rectangular cross section have been studied numerically by using a spectral method, and covering a wide range of the Taylor number ?for a constant Dean number. The rotation of the duct about the center of curvature is imposed in the positive direction, and the effects of rotation (Coriolis force) on the flow characteristics are investigated. As a result, multiple branches of asymmetric steady solutions with two-, three-and multi-vortex solutions are obtained. To investigate the non-linear behavior of the unsteady solutions, time evolution calculations as well as power spectrum of the unsteady solutions are performed, and it is found that the unsteady flow undergoes through various flow instabilities in the scenario “chaotic?→ multi-periodic?→ periodic?→ steady-state”, if Tr is increased in the positive direction. The present results show the characteristics of both the secondary flow and axial flow distribution in the flow.

关键词： Rotating Curved Duct Dean Number Taylor Number Secondary Flow Periodic Solution

Application of the Modified Force-Coupling Method of Tracing the Trajectories of Spherical Bubbles with Solid-Like and Slip Surfaces

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Open Journal of Fluid Dynamics 2017年第4期7卷 657-672页

作者： Chao Guan shinichiro yanase Koji Matsuura Toshinori Kouchi Yasunori Nagata Graduate School of Natural Science and Technology Okayama University Okayama Japan Department of Biomedical Engineering Faculty of Engineering Okayama University of Science Okayama Japan

The force-coupling method (FCM) developed by Maxey and Patel (2001) was modified and applied to trace the trajectories of spherical bubbles with solid-like and slip surfaces. Careful comparison was made to the experimental results of Takemura et al. (2000, 2002a, 2002b). First, the result obtained by use of the original version of the FCM was compared to the experimental results. It was found that the original FCM was not feasible for tracing spherical bubble trajectories. Then, a correction was made to the FCM calculation of the bubble velocity by renormalization in terms of the bubble Reynolds number, which could very well trace the trajectory of the bubble with a solid-like, no-slip surface, but not that of a bubble with a slip surface. Finally, a substantial correction was made to the monopole term of the FCM, which could trace the trajectory of a bubble with a solid-like or slip surface very well even for the Reynolds number up to 20.

关键词： Force-Coupling Method Vertical Wall Spherical Bubble Multiphase Flow

Numerical Study of the Lift Force, Velocities and Pressure Distribution of a Single Air Bubble and Two Interacting Air Bubbles Rising in Quiescent Liquid

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Open Journal of Fluid Dynamics 2020年第1期10卷 31-51页

The study of multiphase flow consisting of liquid and air bubbles has been attracting the interest of many researchers. Numerical methods for such a system are, however, facing difficulty in numerical accuracy and a heavy computational load. In this paper, we made corrections to the modified force-coupling method in our previous papers and applied it to the numerical studies of a single air bubble rising near a vertical wall and two interacting air bubbles rising in line in quiescent liquid. Corrections were made to the effective ranges of the force-coupling method. The calculation results showed that the lift force acting on an air bubble obtained by the experimental data was more accurately reproduced than those by our previous method. We accurately calculated the time evolution of the velocities of interacting two air bubbles rising in line obtained in the previous experiments and resolved the physical mechanism of the relative movement of two bubbles. We also found the present method is much quicker and needs much smaller memory capacity than other methods, such as the volume of fluid method.

关键词： Force-Coupling Method Multiphase Flow Bubble Motion Two Bubble Interaction

A Micromixer Using the Taylor-Dean Flow: Effects of Aspect Ratio and Inflow Condition on the Mixing

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Open Journal of Fluid Dynamics 2015年第3期5卷 256-264页

作者： Yasutaka Hayamizu Toshihiko Kawabe shinichiro yanase Takeshi Gonda Shinichi Morita Shigeru Ohtsuka Kyoji Yamamoto Department of Mechanical Engineering Yonago National College of Technology Tottori Japan Technical Division Tsurumi Manufacturing Co. Ltd. Tottori Japan Graduate School of Natural Science and Technology Okayama University Okayama Japan

Chaotic mixing in three different types of curved-rectangular channels flow has been studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient are imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flow. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In this paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental results and numerical ones. We produced three micromixer models of the curved channel, several centimeters long, with rectangular cross-section of a few millimeters side. The secondary flow is measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. Also we performed three-dimensional numerical simulations with the open source CFD solver, OpenFOAM, for the same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is obtained in the case of De ≤ 0.1 Tr, and it becomes more remarkable when the aspect ratio tends to large. And it is found that the mixing efficiency changes according to the aspect ratio and inflow condition.

关键词： Component Taylor-Dean Flow Chaotic Mixing Secondary Flow LIF CFD

A Micromixer Using the Taylor-Dean Flow: Effect of Inflow Conditions on the Mixing

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Open Journal of Fluid Dynamics 2014年第5期4卷 463-471页

作者： Toshihiko Kawabe Yasutaka Hayamizu shinichiro yanase Takeshi Gonda Shinichi Morita Shigeru Ohtsuka Kyoji Yamamoto Technical Division Tsurumi Manufacturing Co. Ltd. Tottori Japan Department of Mechanical Engineering Yonago National College of Technology Tottori Japan Graduate School of Natural Science and Technology Okayama University Okayama Japan

Chaotic mixing in a curved-square channel flow is studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flows. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In the present paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental and numerical results. We produced a micromixer model of the curved channel several centimeters long with square cross section of a few millimeters side. The secondary flow was measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. We also performed three-dimensional numerical simulations for the exactly same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is achieved for the case of De ≤ 0.1Tr, and that mixing efficiency changes according to the difference in inflow conditions. The flow is studied both experimentally and numerically, and both results agree with each other very well.

关键词： Taylor-Dean Flow Chaotic Mixing Secondary Flow LIF CFD

A Micromixer Using the Chaos of Secondary Flow: Rotation Effect of Channel on the Chaos of Secondary Flow

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Open Journal of Fluid Dynamics 2012年第4期2卷 195-201页

作者： Yasutaka Hayamizu shinichiro yanase Shinichi Morita Shigeru Ohtsuka Takeshi Gonda Kazunori Nishida Kyoji Yamamoto Department of Mechanical Engineering Yonago National College of Technology Tottori Japan Graduate School of Natural Science and Technology Okayama University Okayama Japan

The micromixer, which has a rotor with a curved channel, is studied experimentally. The secondary flow in a curved channel of rectangular cross-section is investigated using PIV (Particle Image Velocimetry) and LIF (Laser Induced Fluorescence) methods. Two walls of the channel (the inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction of the exit of the channel. The non-dimensional channel curvature δ=a/R is taken to be about 0.1, where 2a is the width of the channel, R the curvature radius of the channel. Other non-dimensional parameters concerned are the Dean number De=Reδ1/2, the Reynolds number Re=qdh/v, where q is the mean flow velocity in the channel axis direction, ν the kinematic viscosity, dh the hydraulic diameter of the channel, and the Taylor number Tr=2(2δ)1/2Ωa2/(δv), where Ω is the angular velocity of the rotor. Photographs of the flow in a cross-section at 180° downstream from the curved channel entrance are taken by changing the flux (De) at a constant rotational speed (Tr) of the channel walls. It is found that good mixing performance is obtained in the case of De≤0.1|Tr| and for that case secondary flows show chaotic behaviors. And then we have confirmed the occurrence of reversal of the mean axial flow.

关键词： Chaos Rotation Effect Secondary Flow PIV LIF

Behavior of Motile Sperm in Taylor-Couette Flow: Effect of Shear Stress on the Behavior of Motile Sperm

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Open Journal of Fluid Dynamics 2013年第2期3卷 9-13页

作者： Yasutaka Hayamizu Toru Hyakutake Koji Matsuura shinichiro yanase Shinichi Morita Shigeru Ohtsuka Takeshi Gonda Department of Mechanical Engineering Yonago National College of Technology Tottori Japan Graduate School of Engineering Yokohama National University Yokohama Japan Graduate School of Natural Science and Technology Okayama University Okayama Japan Research Core for Interdisciplinary Sciences Okayama University Okayama Japan

Infertility is often cited as one of the causes of a declining birthrate, which has become a serious social problem in recent years. Processes by which motile sperm can be safely and easily sorted are therefore important for infertility treatment. Therefore, as a new sorting method, microfluidic sperm sorter using the microfluidic system has been developed. To improve more separation efficiency of this device, it is necessary to know the behaviors of motile sperm in the microchannel where the sperm undergo shear flow. The previous study implied the necessity of the modeling of motile sperm in the shear flow. In the present study, therefore, we experimentally investigated the behavior of the motile sperm in the Taylor-Couette flow using PTV (Particle Tracking Velocimetry) method. The experimental results showed that the ascent of the shear stress led to the increase in the sperm velocity, and the direction of the sperm velocity was opposite to that of the flow.

关键词： Motile Sperm Taylor-Couette Flow Shear Stress PTV