The Effect of Translational Vibration with Different Direction on Thermosolutal Convection Onset in a Superposed Fluid and Porous Layers Under Gravity

A linear stability analysis is carried out to investigate the onset of thermosolutal convection in a fluid layer overlying a fluid-saturated porous layer under the high-frequency small-amplitude translational vibration with different direction in the gravitational field. Distinct temperatures and concentrations are applied at the external boundaries of the two-layered fluid-porous domain in such a way that the buoyancy ratio (the ratio of density drop due to concentration difference to that due to temperature difference) has a positive value. The numerical calculations show that transverse (vertical) vibration suppresses convection by delaying its onset when the domain is heated from below. There is a jump-like transition from local to large-scale convective regimes with intensifying vibration. In the case of longitudinal (horizontal) vibration the convection onset value varies non-monotonically: it increases initially, reaches a maximum, and then decreases. The noticeable enhancement of convection is observed at the vibrational Rayleigh-Darcy number close to its value in weightlessness. The longitudinal vibration in contrast to the transverse one is additionally capable of creating convection when the two-layered domain is heated from above. In such a situation the flow has exclusively thermosolutal vibrational nature. With strengthening longitudinal vibration, the critical flow patterns replace each other in the following order: local flows - large-scale flows - long-wave flows with the system of vertically ordered vortexes - "super-shortwave" flows. If one applies at least a small concentration difference across the layers, all of the mentioned vibration effects manifest themselves at less temperature difference and vibration acceleration than they are in the case of pure thermal convection. The thermal and concentration density gradients reinforce each other at positive buoyancy ratios, so heat and mass transfer become most effective.