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

• 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

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

淹没在振荡流中的海崖体绕流是由分离流组成的，分离流具有起动流的流动特性，同时由于振荡流的方向交替，产生长度有限的非定常尾迹。海崖体的受力和流态研究是码头、海底管道等流体工程结构的基础。有许多方面仍然不清楚，但有关流体力引起的振荡流，如波。已有一些关于振荡流动下作用在圆柱上的流体力的实验研究报道。在流体动力学中，Keulegan-Carpenter数和粘性参数β（KC=UmT/D（Um为最大流速，T为周期，D为物体直径），β =Re/KC-D^2 IvT（v为运动粘度）是最重要的参数。 ...更多信息 在U形管水槽中测量了圆柱体的膨胀系数，并与其他研究结果进行了比较，以验证实验装置。然后，在KC数从1到90的宽范围内，测量了具有各种攻角的方柱和平板的纵向力和横向力。流动显示也被用来确认流型和力系数之间的对应关系。结果表明，在测量的KC数范围内，出现了几种不同的流型，涡的运动与纵向力和横向力的变化密切相关。(2)利用U型水槽研究了宽高比为0.2-3.0的矩形柱体在振荡流中的受力和绕流流态。特别地，我们发现d/h=0.6圆柱的阻力系数CD仅在KC=120以后才变得最大，与d/h圆柱在振荡流中的其它情况相比。用有限差分法数值模拟了振荡钝体的绕流问题，用ALE（Arbitrary Lagrangian-Eulerian）有限差分法模拟了振荡钝体的绕流，一个圆柱体和一个方形圆柱体，浸入静水中。在三维、非定常、不可压缩和粘性流动的假设下进行了模拟。预测与流体动力学的测量结果和流动可视化进行了比较。发现计算的和测量的在线力之间有很好的一致性，即，在KC值范围内，由众所周知的Morison方程表示的惯性和阻力系数CM、CD值。数值模拟还成功地再现和识别了几种流型，如圆柱的“纵向涡或本二涡”、“非对称流型”、“横向街道”和“双对”等三维流动结构。计算结果表明，圆柱和方柱的流态与流态可视化结果吻合较好。少

项目成果

A.Okajima, T.Matsumoto, N.Nakasuji, S.Kimura: "Force Measurements on Bluff Bodies and Flow Visualization in Oscillatory Flow." Proc.of 3rd International Colloquim on Bluff Body Aerodynamics and Applications, Blacksburg, VA,USA. CI9-CI (1996)

A.Okajima、T.Matsumoto、N.Nakasuji、S.Kimura：“钝体上的力测量和振荡流中的流动可视化”。

Atsushi OKAJIMA: "Aerodynamic Characteristics of Flat Plates with Various Attacked Angles in Oscillatory Flow" JSME International Journal. Vol.41・No.1. 214-220 (1998)

Atsushi OKAJIMA：“振荡流中具有各种攻角的平板的空气动力学特性”JSME 国际期刊第 41 卷·第 1 期（1998 年）。

Okajima, A., Matsumoto, T., Kimura, S.: "Aerodynamic Characteristics of Flat Plates with Various Angles of Attack in Oscillatory Flow" JSME Int., J., B.41,1. 214-220 (1998)

Okajima, A.、Matsumoto, T.、Kimura, S.：“振荡流中各种攻角平板的空气动力学特性” JSME Int.，J.，B.41,1。

Atsushi OKAJIMA: "Force Measurements and Flow Visualization of Bluff Bodies in Oscillatory Flow" Journal of Wind Engineering and Industrial Aerodynamics. Vol.69-71. 213-228 (1997)

Atsushi OKAJIMA：“振荡流中钝体的力测量和流动可视化”风工程和工业空气动力学杂志。

A.Okajima, T.Matsumoto, S.Kumura: "Aerodynamic Characteristics of Flat Plates with Various Angles of Attack in Oscillatory Flow" JSME CENTENNIAL GRAND CONGRESS.Proc.of International Conference on Fluid Engineering. Vol.1. 513-518 (1997)

A.Okajima、T.Matsumoto、S.Kumura：“振荡流中不同攻角平板的空气动力学特性”JSME CENTENNIAL Grand CONGRESS.Proc.of International Conference on Fluid Engineering。