Influence of skewed three-dimensional sinusoidal surface roughness on turbulent boundary layers

The impact of roughness skewness (ksk) on turbulent boundary layer (TBL) flow with a zero pressure gradient over three-dimensional (3D) sinusoidal rough surfaces was experimentally investigated using single hotwire anemometer. Nine 3D profiles were manufactured positive, negative, and values. Measurements taken at three different freestream velocities for each surface compared smooth wall TBL results. This study covered range friction Reynolds numbers (Reτ) from approximately 1000 to 4000, δ/k≈20 ± 2, where δ represents the local thickness, k is maximum height roughness, measured valley peak. results indicate that wall-unit normalized streamwise mean velocity all exhibit downward shift profiles. Surfaces positive produced highest drag, leading largest shift. coefficient (Cf) decreased as ksk decreased. percentage increase in Cf ΔU+ (the function) much larger when moving negative than skewness. small differences turbulence intensity higher-order statistics outer region support similarity hypothesis considered this study. autocorrelation revealed tend shorten average length structures near-wall region.