Superstructures in inclined thermal convection of low-Prandtl-number fluids

Any tilt of a Rayleigh-Benard convection (RBC) cell against gravity changes the global flow structure inside the cell. Recent experiments by Vasil'ev et al., Tech. Phys. 60 (2015), and Frick et al., Europhys. Lett. 109 (2015), with liquid sodium (Prandtl number Pr=0.0089) demonstrated that the heat transport in low-Pr fluids and for small diameter-to-height aspect ratio containers is especially sensitive to the inclination angle. Our study of inclined convection in a cylindrical container of the aspect ratio 1/5 is based on direct numerical simulations (DNS) and we consider Pr≤1. We demonstrate that flow superstructures like the large scale circulation and boundary layers (BLs) are influenced by both, the inclination angle and the lateral confinement. For inclined convection we observe the formation of two system-sized plume columns, a hot and a cold one, that impinge on the opposite BLs, see Zwirner and Shishkina, J. Fluid Mech. 850 (2018). In RBC the confined cell supports the formation of multiple rolls on top of each other.