The effect of cell tilting on turbulent thermal convection in a rectangular cell

In this study the influence of cell tilting on flow dynamics and heat transport is explored experimentally within a rectangular cell (aspect ratios Γₓ=1 and Γy=0.25 ). The measurements are carried out over a wide range of tilt angles ( 0 β π/2\ rad ) at a constant Prandtl number ( Pr 6.3 ) and Rayleigh number ( Ra 4.42× 10⁹ ). The velocity measurements reveal that the large-scale circulation (LSC) is sensitive to the symmetry of the system. In the level case, the high-velocity band of the LSC concentrates at about a quarter of the cell width from the boundary. As the cell is slightly tilted ( β 0.04\ rad ), the position of the high-velocity band quickly moves towards the boundary. With increasing β , the LSC changes gradually from oblique ellipse-like to square-like, and other more complicated patterns. Oscillations have been found in the temperature and velocity fields for almost all β , and are strongest at around β 0.48\ rad . As β increases, the Reynolds number ( Re ) initially also increases, until it reaches its maximum at the transition angle β=0.15\ rad , after which it gradually decreases. The cell tilting causes a pronounced reduction of the Nusselt number ( Nu ). As β increases from 0 to 0.15, 1.05 and π/2\ rad , the reduction of Nu is approximately 1.4 %, 5 % and 18 %, respectively. Over the ranges of 0 β 0.15\ rad , 0.15 β 1.05\ rad and 1.05 β π/2\ rad , the decay slopes are 8.57× 10⁻² , 3.27× 10⁻² and 0.24\ rad⁻¹ , respectively.