Turbulence modifications in a turbulent boundary layer over spanwise-alternating roughness lanes

摘要

Turbulence modifications over a rough wall with spanwise-varying roughness are investigated at Re_τ≈2,000, using particle image velocimetry (PIV) and hotwire anemometry. The rough wall is comprised of spanwise-alternating longitudinal lanes of two different roughness heights (with a ratio of 8 between the high and low roughness heights). The width of the high-roughness lanes is half of that of low-roughness ones. PIV measurements are performed in a wall-parallel plane located in the logarithmic region, while hotwire measurements are made in a cross-stream plane. In a time-averaged sense, Large-scale counter-rotating roll-modes, are observed in the cross-stream plane over the rough wall, with downwash and upwash common flows displayed over the high- and low-roughness lanes, respectively. Meanwhile, elevated and reduced streamwise velocities occur over the high- and low-roughness lanes, respectively. Significant modifications of Reynolds stresses and vortex activities are also observed, which will be presented in the conference talk.