水平槽道近壁面附近颗粒尾流特性的高分辨率PIV实验研究

Experimental Investigation on the Characteristics of Spherical Particle Wake in a Horizontal Channel Flow by High Resolution PIV

采用PIV测量方法,对不同雷诺数下球形颗粒的尾流特性进行了研究。实验中颗粒是10mm的不锈钢球,距壁面高度G/D(28)0、0.25、0.5和1.0,Rep(28)900、2500和5000,气相示踪粒子为峰值粒径2.5?m的雾化液滴。通过对实验得到的瞬态速度场进行分析,得到时均流线图和速度场。结果表明,G/D(28)0时,整体涡脱落强度明显减小,颗粒下部的漩涡脱落完全被抑制,在颗粒尾部形成一个顺时针回流区,大小约为颗粒尺寸的1.5倍。0.25?G/D?0.5时,壁面的存在使得颗粒尾流结构出现了不对称,呈一定的角度向上倾斜。随着颗粒与壁面距离的增加,壁面对颗粒尾流的影响减弱,在颗粒后缘会出现一对回流区,上方呈顺时针旋转,而下方呈逆时针,且回流区的长度先减小后增大。

The characteristics of sphere particle wake in a horizontal channel flow was experimentally investigated under different Reynolds numbers, using particle image velocimetry（PIV）. A steel ball of size with 10 mm in diameter was used as particle and atomized droplets with peak at about 2.5？m were used as ghost particle. Experiments were performed at Rep（28） 900, 2500, 5000. Time-averaged velocity vectors, patterns of streamlines and vorticity were examined from the point of flow physics for different sphere locations in the range of 0 ？ G/D ？ 1.0 where G was the space between the bottom point of the sphere and wall. It was found that for the case of the sphere touching the wall at G/D（28） 0, a large circulation region formed and covered whole the wake flow region, which size was about 1.5 times of particle diameter. At the gap ratios of G/D（28） 0.25 and 0.5, there is a tendency of the wake to move upward and the two recirculation regions become asymmetric about the sphere centerline. As the gap increased to a value of G/D（28） 1.0, the effect of the wall become weaker dramatically and the asymmetry of streamline decreased. With increasing the gap ratio, the length of the recirculation zone decreased firstly, and then increased.