Magnetic-field effect on thermal convection of a nematic liquid crystal at large Rayleigh numbers
AbstractWe report on near-turbulent thermal convection of a nematic liquid crystal heated from below in a cylindrical cell with an aspect ratio (diameter/height) equal to 0.50 for Rayleigh numbers $2\times 1{0}^{7} \lesssim \mathit{Ra}\lesssim 3\times 1{0}^{8} $ and a Prandtl number of about 355. The Nusselt number $\mathit{Nu}$ as a function of $\mathit{Ra}$ did not differ significantly from that of an isotropic fluid. In a vertical magnetic field $\mathbi{H}$, we found $\mathit{Nu}(H)/ \mathit{Nu}(0)= 1+ a(\mathit{Ra}){H}^{2} $, with $a(\mathit{Ra})= 0. 24{\mathit{Ra}}^{0. 75} ~{\mathrm{G} }^{- 2} $. We present a model that describes the $H$ dependence in terms of a change of the thermal conductivity in the thermal boundary layers due to a field-induced director alignment.