Numerical investigation reveals reduced heat transport from small surface roughness in turbulent thermal convection, indicating fluid entrapment hinders overall heat flux.
Key Points
Investigate whether surface roughness always enhances heat transfer in turbulent Rayleigh–Bénard convection or can under certain conditions decrease it.
Conducted 2D numerical simulations across Rayleigh numbers from 10^7 to 10^11 over rough conducting plates.
Performed 3D simulations at a Rayleigh number of 10^8.
Maintained a constant Prandtl number of Pr = 0.7 for both 2D and 3D simulations.
Observed a reduction in Nusselt number (Nu) for small roughness heights (h), whereas heat-transport enhancement occurred only for larger roughness heights.
Identified a critical crossover roughness height (hc) that scales inversely with the Rayleigh number as hc ~ Ra^(-0.6).
Demonstrated that fluid trapped within cavities between small roughness elements thickens the thermal boundary layer, impeding heat transfer.