图1. (a) 二维水洞装置图,$x$ 方向为重力方向,$y$ 方向为水平方向,$z$ 方向为皂膜厚度方向. 皂膜平面由两根直径为 0.32mm 的尼龙绳组成. 为了形成湍流场,在皂膜上游水平插入一排栅格. 激光器照亮距离栅格为 $S$ 的下游绿色区域,该区域内的流场轨迹信息被两台高速相机捕捉. (b) 栅格布置的实物图. 上方水平排列的圆柱小棒为栅格,竖直的亮线为尼龙绳,两根尼龙绳中间为竖直往下流动的皂膜. 由于 532nm 激光的散射,整个流场呈现绿色背景

Fig.1. (a) Two-dimensional water tunnel setup, $x$ axis is the gravity direction, $y$ axis is the horizontal direction, $z$ axis is the film thickness direction. The plane of soap film is consisted by two nylon ropes whose diameter are 0.32mm. To create turbulent flow, we insert a comb in the upstream. The laser illuminates the downstream regions below the comb, whose flow trajectories are recorded by two high speed cameras. (b) The real image of comb equipment. The upper cylinders make up a comb, the vertical bright lines are nylon ropes, and the soap film flows down between the ropes. The whole flow are in green background, owing the scatter from 532nm laser