Turbulent flow over transitionally rough surfaces with varying roughness densities

Abstract

We investigate rough-wall turbulent flows through direct numerical simulations of flow over three-dimensional transitionally rough sinusoidal surfaces. The roughness Reynolds number is fixed at , where is the sinusoidal semi-amplitude, and the sinusoidal wavelength is varied, resulting in the roughness solidity (frontal area divided by plan area) ranging from 0.05 to 0.54. The high cost of resolving both the flow around the dense roughness elements and the bulk flow is circumvented by the use of the minimal-span channel technique, recently demonstrated by Chung eta al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) to accurately determine the Hama roughness function, . Good agreement of the s..