Experimental determination of the boundaries of the region of existence of anomalous convection flow in an tilted cube

This paper presents an experimentally study of the bifurcation of steady-state air convection in a cubic cavity heated from below under controlled deviations from equilibrium heating conditions due to a slow quasisteady-state tilt of the cavity at a predetermined angle $\alpha$. It is found that in the supercritical range of Rayleigh numbers $\mathrm{Ra}$ at a tilt of the cavity not exceeding $7^{\circ}$, the existence of two stable steady-state convection regimes (normal and anomalous) with circulation in opposite directions is possible. A study is made of the transformations of the temperature distribution in the middle (with respect to the planes in which heat exchangers are located) plane during transition from the anomalous flow regime to the normal regime by instantaneous rotation of the entire mass of air in the cavity around the vertical axis by an angle of $90$ to $135^{\circ}$. It is shown that this rotation occurs when the tilt of the cavity exceeds a critical value $\alpha_{cr}(\mathrm{Ra})$, which was determined experimentally for Rayleigh numbers $0<\mathrm{Ra}<25\mathrm{Ra}_{cr}$, where $\mathrm{Ra}_{cr}$ is the critical Rayleigh number for stability of mechanical equilibrium for heating from below.