Heat transport enhancement by rotating bottom endwall in a cylindrical Rayleigh-Benard convection

Rotating thermal convection, commonly encountered in natural and industrial environments, is typically influenced by both buoyancy forces and boundary rotation. In this study, we conduct direct numerical simulations to explore the effect of rotating bottom on the flow structure and heat transport of Rayleigh-B & eacute;nard convection (RBC) in a cylindrical cavity. This cavity has a radius-to-height ratio of 1 and is filled with an incompressible fluid with a Prandtl number of 0.7. Our results show that the axisymmetric convection pattern, observed in RBC for Ra is an element of[4000,8000] without rotation, transitions into a double roll structure at low rotating speeds ( omega), while for Ra <= 4000, the pattern remains axisymmetric, independent of omega. We then focus on the impact of bottom rotation on heat transport in the axisymmetric regime. Based on the variation in the Nusselt number (Nu) with omega, two distinct regimes are identified: a convection-dominated regime at low omega, where Nu closely resembles that of standard RBC, and a rotation-dominated regime at high omega, where strong shear induced by the rotating bottom intensifies the meridional circulation, significantly boosting global heat flux. The critical rotating speed, omega*, marking the transition between these regimes, follows different power-law relations below and above the buoyant convection onset ( Ra-c): omega*similar to Ra-0.64 for Ra<Ra(c)and omega*similar to Ra0.33 for Ra>Ra-c. As omega increases, the exponents for Nu similar to Ra lambda and Re similar to Ra gamma evolve before converging to lambda approximate to 0.3 and gamma=0.5, respectively. Scaling laws for Nu and Re as functions of omega and Ra in the rotation-dominated regime are finally derived: Nu similar to Ra-0.3 omega(0.64) and Re similar to Ra-0.5 omega.