贴壁方柱湍流场高分辨率PIV实验研究

High-Resolution PIV Measurement of the Wake behind a Square Cylinder Flush-Mounted on the Wall

采用粒子图像速度场测试技术(PIV),测量了低速循环水槽中贴壁二维方柱湍流场.实验中采用了1100万像素CCD相机,所测得的速度矢量空间分辨率达0.72 mm×0.72 mm.通过对该分离再附湍流的1500个瞬时速度场数据进行统计分析,获得时均速度场及时均再附点精确位置,并得到了流向、法向速度分量的脉动强度和涡量场.此外,从流场回流因子分布可知低速回流区在法向的振荡幅度为0.15D(D为方柱截面边长),而沿流向上下游的振荡幅度分别为0.5D和2D,表明旋涡相干结构输运、再附过程以及回流区的低频振荡对流场影响较大.

The separated and reattaching turbulent flow over a two-dimensional square cylinder flushmounted on a plane wall was extensively measured by particle image velocimetry （PIV）. Toward this end, a low-speed recireulation water channel was established a CCD camera with 11 × 10^6 pixels was employed in experiments, by which the spatial resolution of the velocity vectors was determined to 0.72 mm×0.72 mm. Characteristics of the flow were statistically analyzed on 1 500 vector maps in terms of time-averaged vector field, turbulence intensity and vorticity distributions. The distribution of the reverse-flow intermittency in the flow field demonstrates 0.15D variation of the separation bubble in the wall-normal direction, while it reaches 0.5D and 2D in the streamwise direction at the upstream and downstream stations, respectively. This is attributed to the shedding and reattaching motion of large-scale coherent structures, and the low-frequency flapping motion of the separation bubble.