A systematic investigation of roughness height and wavelength in turbulent pipe flow in the transitionally rough regime

Abstract

Direct numerical simulations (DNS) are conducted for turbulent flow through pipes with three-dimensional sinusoidal roughnesses explicitly represented by body-conforming grids. The same viscous-scaled roughness geometry is first simulated at a range of different Reynolds numbers to investigate the effects of low Reynolds numbers and low R0/h, where R0 is the pipe radius and h is the roughness height. Results for the present class of surfaces show that the Hama roughness function ΔU+ is only marginally affected by low Reynolds numbers (or low R0/h), and observations of outer-layer similarity (or lack thereof) show no signs of sensitivity to Reynolds number. Then, building on this, a systemati..