Massive heat transfer enhancement of Rayleigh-Benard turbulence over rough surfaces and under horizontal vibration

We carried out direct numerical simulations of turbulent Rayleigh-Benard convection (RBC) with accounting for both the roughness and the external vibration over the Rayleigh number range 10(7) <= Ra <= 10(11) and the vibration frequency range 0 <= omega <= 1400. The triangular rough elements are uniformly distributed over the top and bottom surfaces, and the vibration is applied in the horizontal direction. It is shown that under the combined action of roughness and horizontal vibration, with increasing the vibration frequency omega, the heat transfer is initially decreased a little and then greatly enhanced after omega exceeds the critical value. The physical reason for massive heat-transfer-enhancement is that high frequency vibration destabilizes thermal boundary layers (BL) over rough surfaces, triggers abundant emissions of thermal plumes, and strengthens the motion of large-scale circulation (LSC), which consequently thins the thickness of thermal BL and heightens the convective transport. In addition, it is shown that vibration-induced heat-transfer-enhancement can obviously affect the scaling behavior between the heat flux and the Rayleigh number, and the scaling exponent increases with increasing omega, whereas the influence of vibration on the scaling behavior between the intensity of LSC and Ra is very weak.