Optimising transport in shear flows over heterogeneous rough walls

A majority of engineering and environmental flows develops over spatially heterogeneous rough surfaces, where the topography of the surface contains a wide variety of length scales. Recent investigations have pointed out that strong secondary currents develop in shear flows over these surfaces, modifying the transport across the shear layer. However, there remain several open questions. For instance, it is not clear what is the leading length scale for the formation of these currents, nor if the formation of these structures is universal across different flows. What is also lacking are tools and understanding to ''engineer'' optimal rough surfaces that, e.g., maximize transport properties, to achieve, e.g. maximum heat transfer or minimum drag. In this project, we will first develop a computational framework based on RANS modelling and adjoint equations that will allow us to design heterogeneous surfaces with optimal attributes. Secondly, complementary DNS of the optimal surfaces will be performed to develop a detailed understanding of the generation mechanisms of secondary currents.