Numerical simulation of a rough-wall pipe from the transitionally rough regime to the fully rough regime

Abstract

Turbulent flow of a rough-wall pipe is simulated using Direct Numerical Simulations (DNS) at low and medium Reynolds number from the transitionally rough regime to the fully rough regime. The rough surfaces simulated consist of three-dimensional sinusoidal roughness elements. The size of the roughness (roughness semi-amplitude height h+ and wavelength λ+) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. A method is developed to accurately calculate the roughness function ΔU+ for the simulations conducted at low Reynolds number. For this surface, the flow is fully rough when h+ ≈ 60 (simulated at Reτ = 540). This corresponds to k..