On non-Oberbeck-Boussinesq effects in cessation-led reversals in Rayleigh-Bénard convection

Abstract eng:
The non-Oberbeck-Boussinesq (NOB) effects on flow reversals in two-dimensional (2D) Rayleigh-Bénard convection (RBC) are studied by direct numerical simulation. The Prandtl number is fixed to 0.71. The flow reversals are triggered by NOB effects when Rayleigh number (Ra) is approximately in the range of 105 S Ra S 1.5 X 107. Once the NOB effects are included, the flow pattern of only one dominant roll, becomes unstable and turns into its symmetric counterpart while the flow circulates clockwise and counter-clockwise in tum, i.e. reversal. The parameter range where flow reversals occur is considerably affected by temperature differential a. It is found the flow reversals are led by the growth in size of the single cold comer roll, and two kinds of physical mechanisms are identified to be responsible for the comer roll's growth: baroclinicity and asymmetry of buoyancy force.

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