The convective motions in a rotating laterally-heated annulus have been studied experimentally. The main feature that differentiates this experiment from others done previously is a rigid lid which is in contact with the fluid. It has been found that the radial temperature differences at which the transition from lower symmetry to the vortex regime occur are different in the cases of positive and negative temperature gradients and that, in particular, the transition is a very strong function of Ω in the case of a negative temperature gradient. It has been observed further that the persisting vortices which form in the annulus always appear at the inner cylinder, whether the radial temperature difference is increased in a quasi-steady way, the radial temperature difference is applied suddenly while the mean temperature is maintained, the heating or cooling is applied suddenly on either the inner or outer cylinder only, thus changing the mean temperature, or whether the rotation of the annulus is started suddenly with the radial temperature difference applied beforehand. This is true regardless of whether the radial temperature gradient is positive or negative and there has not been a single instance in which a persisting vortex developed at the outer cylinder. Neither this observation nor the dependence of the transition temperature difference on Ω seems to be in agreement with the current theoretical descriptions of the annulus motions. On the other hand, the appearance of a warm cell, a counter cell and a cold cell in the time-dependent meridional motions observed in the experiments confirms the results of a numerical study of Williams (1967), which studies the symmetric motions in the annulus.
Turbulent thermal diffusion in a multi-fan turbulence generator with imposed mean temperature gradient
