A genuine technological issue–the thermal convection of liquid in a rotating cavity–is investigated experimentally. The experiments are conducted within a horizontal annulus with isothermal boundaries. The inner boundary of the annulus has a higher temperature, thus exerting a stabilising influence on the system. It is shown that when the layer rotation velocity diminishes, two-dimensional azimuthally periodic convective rolls, rotating together with the cavity, emerge in a threshold manner. The development of convection is accompanied by a significant intensification of heat transfer through the layer. It is shown that the averaged thermal convection excitation in the form of a system of two-dimensional rolls occurs against the background of oscillations of a non-isothermal fluid in the cavity reference frame caused by the gravity field. The excitation threshold and the structure of convective rolls are consistent with the results of the earlier theoretical studies by the authors performed using the equations of “vibrational” convection obtained by the averaging method. Furthermore, the experiments have revealed a new type of averaged flow in the form of a spatially periodic system of toroidal vortices. It is shown that a steady streaming, excited by the inertial oscillations of the fluid, is responsible for the generation of the toroidal vortices. These flows develop in a non-threshold manner and are most clearly manifested in a case of resonant excitation of one of the inertial modes.

Time-averaged thermal convection in a rotating horizontal annulus with a higher temperature at its inner boundary is studied. The centrifugal force plays a stabilizing role, while thermal convection is determined by the “thermovibrational mechanism”. Convective flow is excited due to oscillations of a non-isothermal rotating fluid. Thermal vibrational convection manifests in the form of two-dimensional vortices elongated along the axis of rotation, which develop in a threshold manner with an increase in the amplitude of fluid oscillations. The objective of the present study is to clarify the nature of another phenomenon, i.e., three-dimensional convective vortices observed in the experiments both before the excitation of the convection described above and in the supercritical region. The experimental study of the oscillatory and the time-averaged flow fields by particle image velocimetry is accompanied by the theoretical research of inertial waves. It is found that three-dimensional fluid flows owe their origin to inertial waves. This is confirmed by a high degree of agreement between the experimental and theoretical results. Experiments with cavities of different lengths indicate that the vortices are clearly seen in cavities that meet the conditions of resonant excitation of inertial modes. Furthermore, the length of the cavity has no effect on heat transfer, which is explained by the comparatively low intensity of the wave-induced flows. The main contribution to heat transfer is due to vortices elongated along the axis of rotation. The novel results are of significant practical importance in various fields.