Abstract
Turbulent structure in a boundary layer developed over two different types of three-dimensional rough walls, namely, cavity and protrusion types have been investigated to understand effect of the geometrical feature on the turbulent statistics. Over the protrusion type of rough wall, the local skin friction coefficient is much larger than those of two-dimensional and the cavity type rough wall flows. As momentum thickness Reynolds number increases, the local skin friction coefficient tends to almost the same value over the two-dimensional and cavity type rough walls. Deficit in mean velocity profiles is the largest over the protrusion type of rough wall and takes almost the same value over the two-dimensional and cavity type rough walls. With higher-order moments of fluctuating velocity components, coherent vortical motions near the wall such as hairpin or necklace vortices are discussed to describe turbulent production and diffusion mechanisms in the near wall for the three-dimensional roughness.
