Conditional Reynolds Stress in the Turbulent Near-wall Region onSmooth and Micro-grooved Surfaces

摘要

Measurements in a zero pressure gradient turbulent boundary layer over a V-shaped micro-groovedsurface and a smooth one have been performed using a two-component LDV. The experimental results forthe smooth surface are in good agreement with the existing data. Data obtained in the near-wall regionabove the valley of the grooved surface are compared with those above the smooth surface. The meanvelocity profiles show upward shift in the log-law region for the micro-grooved case. Turbulent intensitiesand turbulent kinetic energy as well as the Reynolds shear stress above the grooves are mitigated.Reynolds shear stress decomposition using quadrant analysis method indicates that grooved surface indrag reduction configuration weakens ejection and sweep events of the turbulent coherent motions, anddecrease the burst frequency of low speed streaks. As a result, the momentum and kinetic exchange areimpeded, which may serve as a clue for unveiling the drag reduction mechanism by grooves.