The impact of random 3D roughness on natural convection along a vertical plate

This study simulates natural convection on vertical surfaces with random roughness under Reynolds number conditions of 106. The roughness of these surfaces is arranged randomly, making the simulation closer to real-world conditions. To handle natural convection in low-speed compressible flows, our solver treats the fluid as compressible to solve the complete Navier-Stokes equations. Observations show that adjacent peaks generate vortices, limiting the heat circulation between valleys and the surrounding cooler air. Influenced by buoyancy, the slower upstream flow over rough surfaces stabilize heat transfer in the valleys and slightly accelerates the flow near the peaks, resulting in higher local Nusselt numbers on the peaks. As the flow velocity increases, the disturbances caused by rough elements become more pronounced, leading to a more chaotic flow pattern downstream, thereby affecting the overall heat transfer. This phenomenon becomes more pronounced with increasing surface roughness. The overall distribution of Nusselt numbers shows higher and more concentrated values upstream compared to downstream. Despite local Nusselt numbers on rough surfaces generally being higher than those on smooth surfaces, the average Nusselt numbers are lower on the rough surfaces due to the longer time required for heat transfer on rough surfaces.