Thermal convection in inclined cylindrical containers

By means of direct numerical simulations (DNS) we investigate the effect of a tilt angle beta, 0 <= beta <= pi/2, of a Rayleigh-Benard convection (RBC) cell of aspect ratio 1, on the Nusselt number Nu and Reynolds number Re. The considered Rayleigh numbers Ra range from 10(6) to 10(8), the Prandtl numbers range from 0.1 to 100 and the total number of the studied cases is 108. We show that the Nu(beta)/Nu(0) dependence is not universal and is strongly influenced by a combination of Ra and Pr. Thus, with a small inclination beta of the RBC cell, the Nusselt number can decrease or increase, compared to that in the RBC case, for large and small Pr, respectively. A slight cell tilt may not only stabilize the plane of the large-scale circulation (LSC) but can also enforce an LSC for cases when the preferred state in the perfect RBC case is not an LSC but a more complicated multiple-roll state. Close to beta = pi/2, Nu and Re decrease with increasing beta in all considered cases. Generally, the Nu(beta)/Nu(0) dependence is a complicated, non-monotonic function of beta.