Vortex dynamics of a low aspect ratio cantilevered cylinder immersed in a boundary layer
Vortex dynamics of a low aspect ratio cantilevered cylinder immersed in a boundary layer
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DOI：
10.1017/jfm.2020.555
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发表时间：
2020-08
影响因子：
3.7
通讯作者：
S. Gildersleeve;M. Amitay
中科院分区：
文献类型：
--
作者：
S. Gildersleeve;M. Amitay
摘要利用油液显示和立体粒子图像测速技术，对小高径比悬臂圆柱销与平板绕流相互作用的流动物理进行了实验研究。对层流、过渡和湍流来流边界层的涡旋结构的相互作用进行了探讨，并研究了流动对附面层中销钉的展宽比及其相对淹没的敏感性。周围的流动对这些参数的细微变化非常敏感(两者都是1阶的)，这是由于销的自由端的流动与其尾迹之间的强烈相关性。这些流动结构受到外部流体夹带和靠近壁面的自诱导和剪切流相互竞争的机制的严重影响。特别是，观测到的涡旋特征在近尾迹中表现出很强的相互依赖性。对于湍流边界层，所形成的“拱形”结构在轴向略有伸展。而在层流入流条件下，剪切强度和湍流强度的降低有利于尾迹的扩大和背风边缘的下洗，形成一个凹形的M型涡旋，影响尾涡对的形成和演化。此外，较大的纵横比会增加进入尾迹的下洗强度，从而为近壁流动提供能量。然而，对于较小的展弦比，由于下洗减少和较弱的切变，涡旋特征之间的相互作用程度降低。文中对这些流动特性进行了详细的讨论。
Abstract The flow physics associated with the interaction of a low aspect ratio, cantilevered cylindrical pin with a flow over a flat plate was investigated experimentally using oil visualizations and stereoscopic particle image velocimetry. The interactions of the vortical structures were explored for laminar, transitional and turbulent incoming boundary layers, where the flow's sensitivity to the pin's aspect ratio and its relative submergence within the boundary layer was studied. The surrounding flow is highly sensitive to subtle changes in these parameters (both are order 1) due to strong dependence between the flow over the pin's free end and its wake. These flow structures are heavily influenced by competing mechanisms of self-induction and shear flow due to outer fluid entrainment and the proximity to the wall. In particular, the observed vortical features exhibit strong inter-dependencies in the near wake. For a turbulent boundary layer, the resultant ‘arch-like’ structure is observed to be slightly stretched in the axial direction. Whereas, under laminar inflow conditions, the reduced shear and turbulence intensity facilitate a wider wake and a stronger downwash from the leeward edge, resulting in a concave ‘M-shaped’ vortex, affecting the formation and evolution of the trailing vortex pair. In addition, larger aspect ratios result in an increased magnitude of downwash into the wake, which re-energizes the near-wall flow. Whereas, for lower aspect ratios, the level of interaction between vortical features decreases due to a reduced downwash and weaker shear. These flow characteristics are discussed in detail in the paper.