Direct numerical simulation study on convective heat transfer of two tandem permeable square cylinders.

This study focuses on two-dimensional heat transfer and unsteady flow past two tandem heated porous square cylinders using lattice Boltzmann method combined with block-structured topology-confined mesh refinement. The effects of the Reynolds number (30 ≤ R e ≤ 150), the Darcy number ( 10 − 5 ≤ D a ≤ 10 − 2 ), and spacing ratio (1.5 ≤ L / D ≤ 5 , where L and D are distance of two adjacent cylinder centers and square cylinder length, respectively) are investigated. The intended analysis links hydrodynamic and heat transfer coefficients and wake structures in parameter space of R e − D a − L / D to fluid mechanics. For upstream cylinder, drag coefficients decrease with a reduction of Da and range of R e ≥ 100 , while wake length increases with an increment of L / D ratio at the same range of Re. Time-averaged normalized velocity increases at higher permeability levels. A significant augmentation in a time-averaged Nusselt number is reported for an increase in Da and full L / D range. For downstream cylinder, the interaction of fluid vortices in the gap between the cylinders affects the flow pattern, causing irregularities in the drag coefficient variation. The impacts of L / D on the wake length is more obvious than that of Da. Both the wake length and time-averaged Nusselt number values are proportional to an increase in L / D. Consequently, all the investigated results of the upstream cylinder are significantly altered from those of the downstream cylinder due to the shadowing effect of the upstream cylinder. [ABSTRACT FROM AUTHOR]