圆盘绕流近尾迹实验研究

Experimental study on the near wake of a circular disk

采用烟线和PIV实验研究Re=22400时直径与厚度比D/H=5圆盘近尾迹(x/D<5)流场结构。流向平面烟线显示表明圆盘尾迹有稳定的回流区和随机扭曲倾斜的三维涡旋结构。对烟线平面PIV测速数据统计平均,发现该回流区具有较好的对称性,且长度为2.1 D。对PIV数据进行POD重构,发现流向雷诺正应力和切应力峰值出现在回流区两侧剪切层,横向雷诺正应力峰值出现在回流区驻点附近,其正是烟线显示涡旋结构脱落区域。圆盘尾迹涡旋结构的产生和脱落源于剪切层的不稳定性及其与回流区的相互作用。圆盘尾迹前两个模态含能仅为10.9%和10.2%,表明湍流结构的随机性;前10个模态含能45.9%可较好描述流场的平均雷诺切应力。

Using smoke wires and PIV technique, the near wake（x/D^5） of circular disk with an aspect of D/H~ 5 at Re-~ 22400 was experimentally studied. Flow visualization using smoke wires showed that there was a stable recirculation zone and stochastic, distorted and tilted three-dimensional vortices behind the disk. By statistic average analysis of a series of cartogra- phies obtained by PIV technique, it was found that the mean flow field was symmetric with a re- circulation zone in length of 2.1D. POD analysis was applied to the PIV data, reconstruction of the first pair of eigenmodes manifested that the peaks of uz and uv located in the shear layer be- tween the free stream and the recirculation zone, and the peak of v2appeared near the stagnation point of the recirculation zone, where vortices were shedding displayed by smoke wires. As a conclusion, vortices generation and shedding in the wake originated from shear layer instability and its interaction with the recirculation zone. The first and second POD modes represent only 10.9% and 10.2% of total turbulent kinetic energy, which means that turbulence structures is relatively stochastic. The first ten modes represent 45.9% of total energy, therefore, the mean Reynolds shear stress can be well described.