圆柱绕流的流场特性及涡脱落规律研究

Experimental research on the flow characteristics and vortex shedding in the flow around a circular cylinder

采用粒子图像测速技术对630、800及950三种雷诺数条件下的圆柱绕流场进行了实验，给出了圆柱下游沿流动方向4倍圆柱直径和垂直方向3倍圆柱直径区域内的速度场、涡量场以及涡脱落现象的时空演化规律．结果表明：圆柱尾流区域位于垂直方向约1．5～2．5倍圆柱直径范围内，随着雷诺数增大，这一范围呈现缩小趋势，而主流对涡的拉伸和输运能力有所增强；涡脱落频率随雷诺数增大而增大，小雷诺数时能够较为完整地捕捉到涡生成、脱落、发展和耗散过程，由于PIV采集频率的限制，大雷诺数条件下涡脱落整个过程不易被完整捕捉到．

The flow around a circular cylinder under the Reynolds numbers of 630, 800 and 950 was studied experimentally by using particle image velocimetry （PIV）. The velocity and vorticity fields were given within the area in the longitudinal direction of 4 times of cylinder diameter and in the lateral direction of 3 times cylinder diameter and the spatial-temporal evolutions of vortex shedding were studied. The experimental results show that the wake is located within the lateral distance with 1.5 to 2.5 times of cylinder diameter, and the distance tends to be reduced as Reynolds number increases while the capabilities of vortex stretching and transport by the main flow increase. The frequency of vortex shedding increases with the increasing of Reynolds number. The process of vortex production, shedding, development and dissipation can be captured basically for the case of small Reynolds number. However, it is difficult to capture the entire process of vortex shedding for high Reynolds number because of the limit of frame grabbing frequency.