展向不同间距壁面粗糙元对近壁湍流拟序结构的影响

采用氢气泡流动显示技术,研究了壁面不同展向间距粗糙元对近壁湍流拟序结构的影响。实验中粗糙元布置在氢泡丝前,其间距按如下两种排列设置：粗糙元直径的0、1和3倍,等间距1、2和4cm;每种情况粗糙元直径均为2.3、4和6mm。基于平均流速和水力直径的流动雷诺数从14000到48000变化。实验观测了光滑壁面和粗糙元壁面的近壁湍流拟序结构条带特征。发现：对于两种不同排列,相同雷诺数和相同粗糙元间距条件下条带有量纲间距均随着粗糙元直径增大而减小,条带有量纲高度均随粗糙元直径的增大而增大;相同雷诺数和相同直径粗糙元条件下条带有量纲间距均随着展向间距增大而增大,条带有量纲高度均随展向间距的增大而减小。粗糙元壁面湍流条带有量纲间距均比光滑壁面小,条带有量纲高度均比光滑壁面大。研究结果对近壁湍流的流动控制具有重要指导意义。

Effects of roughness elements in different spanwise interval arrayal on near-wall turbulence coherent structures

This paper investigates effects of wall roughness elements on near-wall turbulence coherent structures by means of hydrogen bubble flow visualization technology.The roughness elements in diameter of 2.3,4,or 6mm are arranged upstream before the hydrogen bubble wire on the bottom wall for two different ways：multiples of roughness elements diameter and equal-interval.The Reynolds number,based on the mean velocity and channel hydraulic diameter,is changed from 14000 to 48000.The characteristics of near-wall turbulence coherent structures are visualized and analyzed for smooth and rough wall.Both statistical low-speed streak number and vortex height decrease with increasing of the roughness elements interval at the same Reynolds number and roughness elements size.The streak number is greater and the vortex height is higher than those of smooth wall turbulence.The results are valuable for near-wall turbulent flow control.