Experimental and numerical studies of turbulent flows over two-dimensional and three-dimensional rough surfaces under an adverse pressure gradient

The effects of surface roughness and other surface topographical feature on turbulent boundary layer (TBL) development have been widely explored, especially for flow cases with a constant streamwise pressure gradient distribution. In the case where the TBL is exposed to the action of an adverse pressure gradient (APG), flow separation is expected to occur and the classical mechanisms responsible for energy transport between the inner and outer part of the TBL are invalid. The combined effect of roughness and APG on the TBL is not easy to predict, especially due to the lack of databases containing relevant research data. The main aims of the present study were to conduct experimental investigations and to perform large eddy simulations to determine the effects of different surface topographies (two-dimensional (2D) and three-dimensional (3D)) on turbulent flow development over a smooth wall under a strong APG downstream of the corrugation. The investigation was performed with a fixed value of the Reynolds number Re-theta = 4900. In particular, the differences in the production and dynamics of near-wall vortical structures under different corrugation geometries were studied. It was found that the higher amplitude of 2D wavy surface the greater production of turbulence and the earlier separation of the TBL. The response of the TBL differed according to the 3D topography, where it was characterized by a greater streamwise velocity deficit, lower growth of all components of the velocity fluctuations, and a smaller increase in the normal velocity gradient relative to the 2D case with comparable amplitude. The results also demonstrated that the 3D case generated smaller and less energetic structures on the flat plate downstream of the corrugation compared with the 2D case. (c) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

The effects of surface roughness and pressure gradient on turbulent boundary layer development were investigated in this study. The results showed that higher amplitude of the 2D wavy surface increased turbulence production and led to earlier separation of the TBL. In contrast, the 3D topography resulted in a greater streamwise velocity deficit, lower growth of velocity fluctuations, and smaller and less energetic structures downstream of the corrugation compared to the 2D case.