Experiments and Numerical Simulations of Flow Around a Bluff Body in Oscillatory Flow

振荡流中阻流体周围流动的实验和数值模拟

基本信息

批准号：
08455089
负责人：
OKAJIMA Atsushi
金额：
$ 4.99万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08455089/
关键词：
Oscillatory flow U-tube water tank Numerical Simulation Fluid dynamic force coefficients Circular cylinder Rectangular cylinder Flat plate Longitudinal vortices 非定常流後流渦

项目摘要

The flow around a bluff body submerged in oscillatory flow consists of the envelopment of separating flow, which has flow-characteristics of a starting flow and an unsteady wake with a limited length because of flow of the oscillation in the alternate directions. The studies of forces acting upon and flow patterns around the bluff body are fundamental to such fluid engineering constructions as piers, submarine pipelines and other ocean structures. There are many aspects that remain indistinct yet about fluid forces induced by oscillating flow such as waves. Some experimental studies on fluid forces acting on a circular cylinder under oscillating flow were already reported. In this field of fluid dynamics, a Keulegan-Carpenter number and a viscous parameter beta, where KC=UmT/D (Um : a maximum fluid velocity, T : a period, D : a body diameter), beta=Re/KC-D^2IvT (v= kinematic viscosity) are the most important parameters.Experiments by using a U-tube water tank :(1) The fluid dynamic for … More ce coefficients of a circular cylinder were measured and compared with those of other studies in a U-tube water tank to verify the experimental set-up. Then, measurements of both in-line and transverse forces of a square cylinder and flat plates with various angles of attack were made in a wide range of KC numbers from 1 to 90. Flow visualization was also employed to confirm the correspondence between flow patterns and force coefficients. It is found that several classes of flow patterns appear within the measured KC number range and the vortex motions closely corresponds to variations of the in-line and transverse forces.(2) The forces acting upon and the flow patterns around a rectangular cylinder with a cross-section of width/height ratio of 0.2-3.0 submerged in oscillatory flow were studied by using a U-tube water tank. In particular, we found that a drag coefficient CD of the d/h=0.6 cylinder becomes the biggest only beyond KC=120, compared with other case of the d/h cylinder in oscillatory flow. The good relationships between KC number and the flow patterns, and CD and wake width were shown.Numerical Simulations by a finite difference methodAn ALE (Arbitrary Lagrangian-Eulerian) finite difference method has been employed to simulate the flow around an oscillating bluff body, e.g., a circular cylinder and a square one, submerged in a still water. Simulations have been carried out under the assumption of 3-dimensional, unsteady, incompressible and viscous flow. Predictions are compared with the results of measurements of fluid-dynamic forces and flow-visualization. There is found to be good agreement between the computed and measured in-line forces, i.e., the values of inertia and drag coefficients, CM, CD represented by the well-known Morison equation, across a range of KC values. Several types of flow patterns are successfully reproduced and identified by the numerical simulations also, such as 3-D flow-structure of "longitudinal vortices or Honji's Vortex", "asymmetric pattern", "transverse street" and "double pair" for a circular cylinder. It is confirmed that the computed flow patterns agree well with the flow-visualized ones for both the circular cylinder and the square cylinder. Less

围绕着在振动性的振动液中流动的，因为在替代方向上的流动振荡是有限的。作为piers的重物。流体速度，t：一个周期，d：身体直径），beta = re/kc-d^2ivt（v =运动粘度）是最重要的。用U管储罐中的研究测量了圆柱体的更多CE系数，以验证实验设置，测量正方形圆柱体的OTH内线和横向力和具有各种平板的横向力攻击的角度是在1到90的广泛范围内。还采用了流动可视化，以确认力和力之间的对应关系。运动尤其是使用U-Tube水箱，对应于在振荡流中浸入振动流的0.2-3.0的横截面和横截面。 KC数和流动性圆柱体的关系与静止的水和粘性流动众所周知的摩里方程，在一系列KC值中。同意圆柱和方形圆柱体的流动性访问性。