The Evolution of Turbulent Micro-vortices and their Effect on Convection Heat Transfer in Porous Media

TL;DR

This paper investigates how microscale vortices influence turbulent convection heat transfer in porous media, revealing the correlation between vortex dynamics and heat transfer efficiency through LES simulations.

Contribution

It provides new insights into microscale vortex behavior and their impact on heat transfer, aiding the development of improved macroscale models for turbulent porous media flow.

Findings

Vortex attachment/detachment affects local Nusselt number.

Spectral similarity links pressure drag and heat transfer.

Vortex shedding influences overall heat transfer performance.

Abstract

New insight into the contribution of the microscale vortex evolution towards convection heat transfer in porous media is presented in this paper. The objective is to determine how the microscale vortices influence convection heat transfer in turbulent flow inside porous media. The microscale temperature distribution is analyzed using flow visualization in 2D using streamlines and in 3D using Q structures. The pertinent observations are supplemented with the comparison of surface skin friction and heat transfer using: (1) surface skin friction lines and (2) joint PDF of pressure and skin friction coefficients, along with the Nusselt number. The microscale flow phenomena observed are corroborated with the features of the frequency spectra of the drag coefficient and macroscale Nusselt number. The Large Eddy Simulation technique is used to investigate the flow field inside a periodic porous medium. The Reynolds numbers of the flow are 300 and 500. The porous medium consists of solid obstacles in the shape of square and circular cylinders. Two distinct flow regimes are represented by using the porosities of 0.50 and 0.87. The results show that the surface Nusselt number distribution is dependent on whether the micro-vortices are attached to or detached from the surface of the obstacle. The spectra of the macroscale Nusselt number and the pressure drag are similar signifying a correlation between the dynamics of heat transfer and the microscale turbulent structures. Both vortex shedding and secondary flow instabilities are observed that significantly influence the Nusselt number. The fundamental insight gained in this paper can inform the development of more robust macroscale models of convection heat transfer in turbulent flow in porous media.