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

In the study, the influence of cell tilting on flow dynamics is explored experimentally in a rectangular cell (aspect ratios Gamma(x) = 1 and Gamma(y) = 0.25 ). The measurements are carried out in a wide range of tilt angles (0 <= beta <= pi/2 rad) at Prandtl number (Pr similar or equal to 6.3 ) and Rayleigh number (Ra similar or equal to 4.42 x 10(9) ). With the velocity measurements, the large-scale circulation (LSC) is found to be sensitive to the symmetry of the system. In the level case, the LSC is at about quarter width of the cell. As the cell is slightly tilted (beta similar or equal to 0.04 rad), the LSC moves quickly towards the boundary. With increasing beta , the LSC changes gradually from oblique ellipse-like to square-like, and to more complicated patterns. Oscillation has been found for almost all beta, and are strongest at around beta similar or equal to 0.48 rad. As beta increases, the Reynolds number (Re) initially also increases, until it reaches its maximum at the transition angle beta = 0 .15 rad, after which it gradually decreases. The cell tilting causes a pronounced reduction of the Nusselt number (Nu). As beta increases from 0 to 0.15, 1.05 and pi/2 rad, the reduction of Nu is approximately 1.4 %, 5% and 18 %, respectively. Over the ranges of 0 <= beta <= 0.15 rad, 0.15 <= beta <= 1.05 rad and 1.05 <= beta <= pi/2 rad, the decay slopes are 8.57 x 10 (2), 3.27 x 10 (2) and 0.24 rad (-1), respectively.