Lattice Boltzmann simulations of flow and heat transfer from a permeable triangular cylinder under the influence of aiding buoyancy

Mesoscopic numerical simulations have been carried out to learn about the flow and heat transfer characteristics of a 2-D permeable triangular cylinder, aligned at two different orientations under the influence of aiding buoyancy. Objective of this study is to investigate the effects of Darcy number and forebody shape on the hydrodynamic and thermal behaviour of the porous cylinder, under forced convection (i.e. Ri = 0) and aiding buoyancy conditions (Ri = 0.5 and 1) for a Prandtl number value of 0.71 (air). The ranges of Reynolds number (Re) and Darcy number (Da) considered in this study are 1 <= Re <= 40 and 10(-6) <= Da <= 10(-2), respectively. Lattice Boltzmann method with two distribution functions is employed to perform the numerical experiments. Alongwith BGK collision operator, a body force term with viscous and inertial effects of the porous medium is employed at the porous zone. Detailed results are exhibited in the form of wake length, drag coefficient, streamlines, isotherm contours, heat transfer enhancement ratio and mean Nusselt number. Furthermore, a comparative investigation of drag coefficient and mean Nusselt number of permeable triangular cylinder (apex and side facing flow) with that of the square cylinder is carried out at Da = 10(-6) for different buoyancy levels. Under aiding buoyancy condition (i.e. Ri > 0), the side facing triangular cylinder experiences less drag force than the apex facing for all values of Da. A significant thermal dissipation is observed for increasing values of non-dimensional permeability (or Da) and Richardson number. Furthermore, simple expressions for mean Nusselt number, valid for the range of parameters embraced in the present study, are also provided. The appropriate selection of non-dimensional permeability under different buoyancy conditions is important while applying porous media modeling technique in diverse fields of engineering. (C) 2017 Elsevier Ltd. All rights reserved.