Dynamic Behavior of Separation Vortices around a Pitching and Heaving Airfoils and Dynamic Forces

俯仰和起伏翼型周围分离涡的动态行为和动态力

• 批准号: 13650187
• 负责人: TANAKA Kazuhiro
• 金额: $ 2.62万
• 依托单位: Kyushu Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650187/
• 关键词: Unsteady Flow; Separation; Airfoil; Pitching Motion; Heaving Motion; Vortex; Wake; Thrust

Many studies on unsteady separation around a moving airfoil have been carried out with the numerical and experimental approaches. Most of them have been performed for high Reynolds number region over Re = 10^6. Recently, a few studies on the unsteady flow at low Reynolds number region have been developed by the interest in the micro-electro-mechanical-systems (MEMS) based on the concept of flow control. On the other hand, the propulsion mechanisms of aquatic animals, birds and insects have also been attracted. However, the relationship between the vortex structure behind the moving airfoil and the dynamic thrust acting on them for low Reynolds number region have been understood sufficiently. In this study, the wake structure behind the moving airfoil and the dynamic behaviors of vortices near the trailing edge of them have been visualized in a water tunnel for low Reynolds number region, and the dynamic thrust acting on them have been measured by using a six-axes sensor.In the case of quarter-chord axis with higher non-dimensional pitching rate and large pitching amplitude, the distance between the vortices in the thrust producing vortex street was much shorter. It was considered that the jet was produced behind a pitching airfoil. As a result, the large dynamic thrust was produced in almost regions during one pitching cycle and the averaged dynamic thrust during one pitching cycle increased as the non-dimensional pitching rate increased. It was necessary to form the thrust producing vortex street with short distance between vortices in order to generate the large dynamic thrust.

已经通过数值和实验方法对运动翼型周围的非稳态分离进行了许多研究。其中大多数是针对 Re = 10^6 以上的高雷诺数区域执行的。最近，由于对基于流动控制概念的微机电系统（MEMS）的兴趣，一些关于低雷诺数区域非定常流动的研究已经展开。另一方面，水生动物、鸟类和昆虫的推进机制也被吸引了。然而，低雷诺数区域运动翼型背后的涡结构与作用在其上的动态推力之间的关系已经得到充分理解。在本研究中，在低雷诺数区域的水洞中对运动翼型后面的尾流结构及其后缘附近的涡流动态行为进行了可视化，并使用六轴测力计测量了作用在其上的动态推力。在无量纲俯仰速率较高、俯仰幅度较大的四分之一弦轴的情况下，产生推力的涡街中涡之间的距离要短得多。人们认为喷射是在俯仰翼型后面产生的。结果表明，在一个俯仰周期内，几乎所有区域都产生了较大的动推力，并且随着无量纲俯仰速率的增大，一个俯仰周期内的平均动推力也随之增大。为了产生大的动推力，需要形成涡间距短的产生推力的涡街。