Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime

Abstract

Direct Numerical Simulations (DNS) are earned out in a turbulent rough-wall pipe at low and medium Reynolds numbers. The rough surface, which is comprised of three-dimensional sinusoidal roughness elements, was viscously scaled from the transitionally rough regime to the fully rough regime. The main aim of this study is to analyse the behaviour of the near-wall cycle as the surface condition changes from smooth through to fully rough. When analysing the streamwise velocity, a triple decomposition is used to distinguish between the fluctuations due to the spatial variation with the actual turbulent fluctuations. For small roughness height (h+ < 15), the near-wall cycle streaks occurs above th..