Effects of rough walls on sheared annular centrifugal Rayleigh-Bénard convection

In this study, we investigate the coupling effects of roughness and wall shear in an annular centrifugal Rayleigh-Bénard convection system, where two cylinders rotate with different angular velocities. Two-dimensional direct numerical simulations are conducted within a Rayleigh number range of 106≤Ra≤108, and the nondimensional angular velocity difference (ω), representing wall shear, varied from 0 to 1. The Prandtl number is fixed at Pr=4.3, the inverse Rossby number at Ro-1=20, and the radius ratio at η=0.5. The interaction between wall shear and roughness leads to distinct heat transfer behavior in different regimes. In the buoyancy-dominant regime, an increase in the nondimensional angular velocity difference (ω) significantly enhances heat transfer. However, as ω continues to rise, a sharp reduction in heat transfer is observed in the transitional regime. Beyond a critical value of ω, the flow enters a shear-dominant regime, where heat transfer remains unchanged despite further increases in ω. The underlying mechanisms behind these distinct heat transfer behaviors are then elucidated. The enhancement of heat transport in the buoyancy-dominant regime is attributed to the introduction of external shear by the rotating rough walls, which reinforces convection and secondary flows within the cavities. Additionally, these secondary flows improve the efficiency of transporting the trapped hot and cold fluids outside the cavities, further enhancing heat transfer. However, in the transitional regime, the number of convection rolls rapidly decreases with increasing shear, eventually reaching a point where sustaining them becomes challenging. Consequently, a sharp reduction in heat transfer occurs. In the shear-dominant regime, heat transfer is primarily governed by diffusion, leading to a constant heat transport rate.