Pore-scale large eddy simulation of turbulent flow and heat transfer over porous media

Abstract

• Fluid flow and heat transfer in a composite porous-fluid system is explored using LES. • Portion of the fluid entering to the porous region leaks to the non-porous region. • Counter-rotating vortex pairs is observed within and above the porous region. • Contour of temperature shows Kelvin-Helmholtz instabilities above the interface. • In contrast to the solid block, flow laminarisation occurs on the porous block. This paper investigates turbulent fluid flow and heat transfer over a porous medium in a channel using pore-scale large eddy simulation. Special attention is placed on the exchange of heat and flow between the porous and non-porous regions through the interface between the two regions. For this purpose, two different porous systems made of a packed bed of spheres and rectangular rods are analysed and the results are compared against a solid block case of the same size. Flow visualization shows that a significant portion of the fluid entering the porous blocks leaks from the porous region to the non-porous region through the porous-fluid interface. To discuss the effects of this flow leakage on the flow features and heat transfer, discussions are made regarding velocity, pressure, and temperature fields, as well as coherent structures, and turbulence production. The flow pattern inside the porous region indicates that the flow leakage clogs the pore channels inside the porous medium which induces a significant reduction in the streamwise momentum of the pore flow. In addition, coherent structures show that flow leakage leads to the creation of counter-rotating vortex pairs of fluid flow within and above the porous block that results in the formation of organized hairpin structures. Finally, the comparison of turbulence production for the porous and solid cases together with the onset growth of the Kelvin-Helmholtz instability on the porous-fluid interface show a reduction in turbulent kinetic energy above the leading edge of porous blocks. This observation implies that for the porous cases the transition to turbulence is postponed to the downstream of the porous block and it is not achieved as fast as the solid block.