Abstract

While our understanding of turbulence (particularly drag) over rough walls is relatively mature, we know much less about how other types of surface complexities such as chemical contrasts, fouling, pores, and compliance modify turbulence and thereby drag and heat transfer coefficients. The study of such surfaces is not only relevant for the prediction and control of turbulence, but it also provides physical insight into wall-bounded turbulence, particularly with respect to the emergence of surface-induced instabilities and other interactions of a modulating nature. I will first give an overview of ‘where we stand’ regarding turbulence over complex surfaces, highlighting the outstanding scientific questions. Then, I will describe our efforts in i) using homogenization and data-driven approaches to predict the roughness function in the transitionally and fully rough regimes; ii) characterizing coherent structures, entrainment and amplitude modulation of flows over anisotropic porous media and iii) controlling drag and heat transfer using slippery lubricated surfaces.