Time-resolved and volumetric PIV measurements of a transitional separation bubble on an SD7003 airfoil
Time-resolved and volumetric PIV measurements of a transitional separation bubble on an SD7003 airfoil
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DOI：
10.1007/s00348-007-0421-0
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发表时间：
2008-04-01
影响因子：
2.4
通讯作者：
Schroeder, W.
中科院分区：
文献类型：
--
作者：
Burgmann, S.;Dannemann, J.;Schroeder, W.
为了全面了解Kelvin-Helmholtz不稳定性对翼型吸力侧过渡分离气泡扑动的影响及其对翼型性能的影响，研究了分离气泡下游端涡的时空结构。由于气泡的变化会引起压力分布的变化，因此对瞬时速度场的研究对于了解翼型整体性能的细节是必不可少的。对SD7003翼型上表面再附区在不同攻角下的涡系形成进行了详细分析。在雷诺数Re-c为100000的情况下，层流边界层在迎角为4度时分离。由于过渡过程，分离的剪切层在局部受限的回流区周围发生湍流再附着。为了确定分离气泡的位置并描述再附着的动力学，在单个光片上进行了时间分辨的PIV测量。为了阐明再附着区流型在时间和空间上的空间结构，应用了立体扫描PIV装置。流场被记录在至少十个连续的光片平面上，利用两个环绕65度视角的高速相机来检测光片内的所有三个速度分量，由于扫描速度高，导致了时间分辨体积测量。测量结果证实了准周期涡旋结构的发展。给出了由Kelvin-Helmholtz(KH)不稳定性初始化的涡旋卷起的时间动力学和涡卷过程的空间发展。在此基础上，提出了一个由C形涡的形成及其向螺丝刀的转变所组成的旋涡结构演化模型。
To comprehensively understand the effects of Kelvin-Helmholtz instabilities on a transitional separation bubble on the suction side of an airfoil regarding as to flapping of the bubble and its impact on the airfoil performance, the temporal and spatial structure of the vortices occurring at the downstream end of the separation bubble is investigated. Since the bubble variation leads to a change of the pressure distribution, the investigation of the instantaneous velocity field is essential to understand the details of the overall airfoil performance. This vortex formation in the reattachment region on the upper surface of an SD7003 airfoil is analyzed in detail at different angles of attack. At a Reynolds number Re-c 100,000 the laminar boundary layer separates at angles of attack >4 degrees. Due to transition processes, turbulent reattachment of the separated shear layer occurs enclosing a locally confined recirculation region. To identify the location of the separation bubble and to describe the dynamics of the reattachment, a time-resolved PIV measurement in a single light-sheet is performed. To elucidate the spatial structure of the flow patterns in the reattachment region in time and space, a stereo scanning PIV set-up is applied. The flow field is recorded in at least ten successive light-sheet planes with two high-speed cameras enclosing a viewing angle of 65 degrees to detect all three velocity components within a light-sheet leading to a time-resolved volumetric measurement due to a high scanning speed. The measurements evidence the development of quasi-periodic vortex structures. The temporal dynamics of the vortex roll-up, initialized by the Kelvin-Helmholtz (KH) instability, is shown as well as the spatial development of the vortex roll-up process. Based on these measurements a model for the evolving vortex structure consisting of the formation of c-shape vortices and their transformation into screwdriver vortices is introduced.