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The focus of this paper is to systematically study the influence of solidobstacle surface roughness in porous media on the microscale flow physics andreport its effect on macroscale drag and Nusselt number. The Reynolds averagedflow field is numerically simulated for a flow through a periodic porous mediumconsisting of an in-line arrangement of square cylinders with square roughnessparticles on the cylinder surface. Two flow regimes are identified with respectto the surface roughness particle height: fine and coarse roughness regimes.The effect of the roughness particles in the fine roughness regime is limitedto the near-wall boundary layer around the solid obstacle surface. In thecoarse roughness regime, the roughness particles modify the microscale flowfield in the entire pore space of the porous medium. In the fine roughnessregime, the heat transfer from the rough solid obstacles to the fluid insidethe porous medium is less than that from a smooth solid obstacle. In the coarseroughness regime, there is an enhancement in the heat transfer from the roughsolid obstacle to the fluid inside the porous medium. Total drag reduction isalso observed in the fine roughness regime for the smallest roughness particleheight. The surface roughness particle spacing determines the fractional areaof the solid obstacle surface covered by recirculating, reattached, andstagnating flow. As the roughness particle spacing increases, there are twocompeting factors for the heat transfer rate: increase due to more surface areacovered by reattached flow, and decrease due to the decrease in the number ofroughness particles on the solid obstacle surface. Decreasing the porosity andincreasing the Reynolds number amplify the effect of the surface roughness onthe microscale flow.

Flow regimes and types of solid obstacle surface roughness in turbulent heat transfer inside periodic porous media