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Nonlinear Interaction between Motion of a Sphere and an Unsteady Fluid Flow in a Small-diameter Tube

球体运动与小直径管内不稳定流体流动的非线性相互作用

基本信息

批准号：
15560205
负责人：
YOSHIZAWA Masatsugu
金额：
$ 2.37万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15560205/
关键词：
Fluid micro machine Flow -induced vibration Nonlinear mechanical phenomena Numerical simulation Similarity law PIV Symmetrical three-dimensional flow 相似糢型実験渦剥離抗力係数

项目摘要

Recently, there are so many researches and developments in order to design and make the micro machine in blood vessels. The unsteady fluid flow in a small diameter tube is laminar and the effect of viscosity becomes so large that it can no more be disregarded as compared to gravity and inertia. The behavior of fluid flow will be dynamically unstable and many flow patterns will occur due to the small clearance between a sphere and the tube. However, there is still so few researches associated with such phenomena because it is difficult to analyze in a three dimensional space.This research investigates numerically and experimentally the motion of a sphere of density ρ_s and diameter D_s, and flow field in small-diameter tube filled with fluid of density ρ and kinematic viscosity υ, under the external constant force of gravity acceleration G parallel to the pipe axis. The marker and cell method is used to calculate numerically, and the flow field is assumed to be axisymmetric. There are three dimensionless parameters in this system, i.e., Galilei No.Ga=D_s^3G/υ^2, the tube-diameter ratio d=D/D_s, and the density difference ratio α=(ρ_s - ρ)/ρ. The tube-diameter ratio d and the density difference ratio α are changed in this research, though Ga is constant.As a main result, the following conclusions are obtained from the numerical analysis ;(1)The dimensionless terminal velocity of a sphere ν_<bterr>=V_<Bter>υ/(αD_s^2G) does not change with increasing the product of α and Ga for the case that d is small value.(2)The streamline around a moving sphere in a small-diameter tube is elliptical. The length of streamline behind a sphere increases with increasing d and αGa.The theoretically predicted characteristics of unsteady laminar fluid flow around the sphere and the motion of the sphere are confirmed qualitatively in experiments.

近年来，为了设计和制造血管内的微型机械，人们进行了大量的研究和开发。小直径管内的非定常流体流动是层流，粘性的影响变得如此之大，以至于与重力和惯性相比，它不能被忽略。由于球体与管道之间的间隙很小，流体流动的行为将是动态不稳定的，并且会出现许多流动模式。本文通过数值模拟和实验研究了在平行于管轴的恒定重力加速度G作用下，密度为ρ_s、直径为D_s的球体在充满密度为ρ、运动粘度为D_s流体的小直径管内的运动和流场。数值计算采用标记网格法，流场假设为轴对称。在这个系统中有三个无量纲参数，即，Galilei No.Ga=D_s^3G/D_s^2，管径比d=D/D_s，密度差比α=（ρ_s - ρ）/ρ。在Ga不变的情况下，改变管径比d和密度差比α，通过数值分析得到以下主要结论：（1）当d较小时，球的无因次终端速度v_<bterr>=V_<Bter>∞/（αD_s^2G）不随α与Ga乘积的增大而变化。（2）小直径管内运动球体绕流的流线是椭圆的。球后流线的长度随d和αGa的增大而增大，理论预言的非定常层流绕球流动和球运动的特性在实验中得到了定性的证实。