Taylor-Couette and Rayleigh-Bénard turbulence: the role of the boundaries

It is hard to overestimate the importance of turbulent convection, either thermally driven or driven by rotation, for a deeper understanding of various natural phenomena. In the lab, the two most popular fundamental configurations to perform research in turbulent convection are Taylor-Couette (TC) flow–the flow bounded between two independently coaxial rotating cylinders, and Rayleigh-Bénard (RB) flow–the flow in a box heated from below and cooled from above. They have been used to test new concepts for fluid dynamics, starting from linear instability, to nonlinear dynamics and chaos, to pattern formation, and to turbulence. Over the years, much attention has been paid to the scaling relations between the driving forces and the global transport properties. It has been found that the interplay between the boundary layer and bulk flow determines these scaling relations. Thus, it is important to modify the boundaries to probe how the system responds and to better understand the role of BLs. The simplest way is to change the boundary from smooth to rough. In this thesis, we focus on TC and RB turbulence with wall roughness. The key questions we ask in this thesis are that: How does the change of boundary affect the flow structure and the scaling laws in TC and RB turbulence? Is it possible to achieve the asymptotic ultimate regime with wall roughness? Do different types of roughness (symmetry or asymmetry, height, shape, sparseness) have different effects on the transport?