基于时间解析PIV的圆柱绕流尾迹特性研究

采用时间解析PIV（采样频率为1000Hz）在0.55m×0.4m声学风洞中测量了直径D=20mm圆柱后方7.5倍直径、圆柱两侧各3.3倍直径所围成范围内的绕流尾迹在雷诺数Re=2.74×104下的非定常流场。针对PIV获得的速度场数据，进行流场和频谱特性分析，探讨了圆柱绕流尾迹中的平均流场和脉动流场特性，以及旋涡脱落的频率特性。提出了基于速度场之间相关性的相位平均分析方法，系统分析了圆柱上下两侧旋涡交替生成、脱落、发展并耗散的完整演化过程。结果表明:在圆柱后方存在一个低速回流区，其中心0.8D的位置附近是流动结构变化最剧烈的区域；圆柱后方1.9D位置附近是上/下两侧脱落旋涡交汇、耦合的区域，湍流脉动最强；圆柱绕流尾迹中，旋涡脱落频率对应的斯特劳哈尔数稳定在0.2左右；基于速度场之间相关性的相位平均分析方法简单有效，可以准确地识别绕流尾迹中旋涡交替脱落和发展的时空演化过程，在非定常流场测量方面具有普遍推广意义。

Measurements of circular cylinder's wake using time-resolved PIV

Time-resolved particle image velocimetry (PIV) with sampling frequency f=1000Hz was used in 0.55m×0.4m aeroacoustic wind tunnel to test the unsteady characteristics of the flow behind a D=20mm diameter circular cylinder in an area of 7.5 times the diameter long and 6.6 times the diameter wide at Reynolds numbers of 2.74×104.The characteristics of the mean and pulsating flow fields, as well as the frequency characteristics of the cylinder's wake have been revealed.A phase-averaged analysis method based on the cross-correlation coefficients among the PIV velocity vectors has been proposed to capture the process of vortex production, shedding, development and dissipation.The results indicate that there exists a low-speed recirculated flow area behind the circular cylinder, where the flow structure changes most intensively.The vortices shed from the upper and lower sides of the circular cylinder cross and correlate around the 1.9D downstream area, where the turbulence is the strongest.Strouhal number corresponding to the vortex shedding frequency of the cylinder's wake is stable around 0.2.The proposed phase-averaged analysis method is simple but efficient to study the spatial-temporal evolutions of the vortex shedding, which can be easily applied to other areas in unsteady flow field measurement.