Thermal Convection in a Tilted Rectangular Cell with Aspect Ratio 0.5

Thermal convection in a three-dimensional tilted rectangular cell with aspect ratio 0.5 is studied using direct numerical simulations within both Oberbeck-Boussinesq (OB) approximation and strong non-Oberbeck-Boussinesq (NOB) effects. The considered Rayleigh numbers Ra range from 10(5) to 10(7), the working fluid is air at 300 K, and the corresponding Prandtl number Pr is 0.71. Within the OB approximation, it is found that there exist multiple states for Ra = 10(5) and hysteresis for Ra = 10(6) For a relatively small tilt angle beta, the large-scale circulation can either orient along one of the vertical diagonal planes (denoted by M-d mode) or orient parallel to the front wall (denoted by M-p mode). Which of the two modes transports heat more efficiently is not definitive, and it depends on the Rayleigh number Ra For Ra = 107 and beta=0 degrees, the time-averaged flow field contains four rolls in the upper half and lower half of the cell, respectively, Ra and M-p modes only developing in tilted cells. By investigating NOB effects in tilted convection for fixed Ra = 10 6, it is found that the NOB effects on the Nusselt number Nu., the Reynolds number Re and the central temperature T-c for different beta ranges are different. NOB effects can either increase or decrease Nu, Re and T-c when beta is varied.