Onset of Horizontal Convection

Horizontal convection describes natural convection flow driven in an enclosure by non-uniform heating imposed across a horizontal boundary. Research has predominantly focused on the dynamics of horizontal convection in thermal equilibrium, where net heat flux through the forcing boundary or any horizontal level in the flow is zero. However, its early transient features and the dynamics of the transition to unsteady flow are not well understood. The current study numerically investigates the onset of horizontal convection with piecewise constant temperature and uniform heat flux along a bottom boundary of a rectangular enclosure. The onset is found to be characterised by an initial conduction phase followed by a Rayleigh-Bénard type of convection through the thermal boundary layer and finally, bulk overturning flows are established within the enclosure. These regimes and the effects of different heat flux amplitudes and frequencies on the onset of horizontal convection are characterised in the present work.