Effect of surface roughness element on near wall turbulence with zero-pressure gradient

• Published in: Science China. Physics, mechanics & astronomy Vol. 58; no. 6; pp. 95 - 102
• Main Authors: Zhang, Xin, Pan, Chong, Shen, JunQi, Wang, JinJun
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.06.2015; Springer Nature B.V
• Subjects: Astronomy; Boundary layers; Classical and Continuum Physics; Fluid dynamics; Fluid flow; Kinematics; Low speed; Observations and Techniques; Physics; Physics and Astronomy; Probability distribution; Regularization; Roughness; Statistical analysis; Streak; Surface roughness; Surface roughness effects; Turbulence; Turbulent boundary layer; Turbulent flow; Walls; 元素; 压力梯度; 条纹间距; 湍流边界层; 脉动强度; 表面粗糙度; 运动效果; 近壁湍流; 064702; turbulent coherent structures; low-speed streak; flow control
• ISSN: 1674-7348; 1869-1927
• DOI: 10.1007/s11433-015-5677-4

In the present paper, we present an investigation on the effect of roughness elements onto near-wall kinematics of a zero- pressure-gradient turbulent boundary layer. An array of spanwisely-aligned cylindrical roughness elements was attached to the wall surface to regulate the near-wall low-speed streaky structures. With both qualitative visualization and quantitative meas- urement, we found that the regularization only occurs in the region below the height of the roughness elements. Statistical analysis on the probability distribution of the streak spanwise spacing showed that the mean spanwise streak spacing is domi- nated by the roughness elements; however, the latter＇s effect is in competition with the intrinsic streak generation mechanisms of smooth wall turbulence. Below the top of the roughness elements, local streamwise turbulent fluctuation intensity can be reduced by about 10%. We used POD analysis to depict such regularization effect in terms of near-wall structure modulation. We further found that if the spanwise spacing of roughness elements increased to be larger than the mean streak spacing in the smooth wall turbulence, there is no streak-regularization effect in the buffer region, so that the near-wall streamwise turbulent fluctuation intensity doesn＇t reduce.