MIXED CONVECTION FLOW AND HEAT TRANSFER PHENOMENA ACROSS TRAPEZOIDAL BLUFF BODIES: A COMPARATIVE STUDY

Abstract

Two-dimensional numerical simulations have been realized to explore and evaluate the laminar mixed convection flow and heat transfer across a heated trapezoidal bluff body in an unconfined domain. Two different configurations of the trapezoidal bluff body viz. expanded and tapered have been considered and a comparison has been evaluated at different operational parameters. The spectrum of physical control parameters considered as Reynolds number (Re)=10-50, Richardson number (Ri)=0-1 and Prandtl number (Pr)=0.7 (air). A finite volume method implemented on the collocated grid arrangement has been employed for numerical computations. The flow and heat transfer characteristics have been represented by streamline and isotherm contours respectively at varying values of Re and Ri. Drag and lift coefficients for the tapered body is found higher as compared to the expanded body for same operating conditions. However, average Nusselt number is greater for an expanded body as compared to a tapered body. With increase in Re at a given Ri, drag coefficient is found to decrease in steady regime, but it increases in time-periodic regime. On advancing Ri, drag and lift coefficients decrease for the steady state regime for both the geometries. A correlation expressing the functional relationship of average Nusselt number with Re and Ri for both geometries have been proposed. Critical Reynolds number at Ri=0.5 for the expanded geometry is found to be between Re=46 and 47, while for the tapered body it is found to be between Re=35 and 36. Maximum heat transfer enhancement for the expanded body at Ri=0.5 and Ri=1 with respect to Ri=0 is found to be approximately 8.5% and 2% respectively. Similarly, for the tapered body maximum augmentation in heat transfer for the above mentioned conditions is found to be approximately 6% and 2%. Maximum heat transfer enhancement for the tapered body with respect to the expanded body at Ri=0, 0.5 and 1 is found to be approximately 26%, 24% and 21% respectively