LAMINAR CROSS-BUOYANCY MIXED CONVECTION AROUND A CONFINED TRIANGULAR BLUFF BODY

Abstract

Ihe numerical simulations in 2-D are carried out to investigate the effects of cross-buoyancy on the flow and heat transfer characteristics over an equilateral triangular bluff body placed at the central axis of horizontal channel with its vertex facing the flow, at low and intermediate Reynolds numbers. The results are generated for the ranges of control parameters as I< Re <150 and Richardson number (Ri) = 0-2. The pressure-velocity coupling equations are resolved by using SIMPLE algorithm on a collocated grid system. The variations in overall drag coefficients, lift coefficients, Strouhal number and average Nusselt number are found and discussed for the preceding conditions, to conclude as to how the control parameters like Reynolds and Richardson numbers effect the confined flow and heat transfer phenomena. For all the three Richardson numbers studied, it was found that there is a decrease in overall drag coefficient with increasing Reynolds number up to around Re=100. Thereafter the total drag coefficient (CD) shows an increasing trend. For a fixed Richardson number (Ri), an average Nusselt number (Nit is found to increase with increasing Reynolds number. However, at any fixed Reynolds number an average Nusselt number shows soft but varying response towards increasing buoyancy (Ri>0). The percentage enhancement of approximately 3% in an average Nusselt number is lound for Re40, for all values covered under this study while comparing the values of average Nusselt number at Ri=l and 2 with respect to that at Ri0. A simple heat transfer correlation is given to relate the values of Nu and Re for Richardson numbers 1 and 2. Furthermore, extensive simulations have been carried out to calculate the critical Reynolds numbers (Ret) showing the transition of flow from a symmetric to a periodic regime with changing Richardson numbers. As the critical Reynolds number for the forced convection (Ri0) is reported elsewhere (Srikanth et al. 2010), for the mixed convection the Re values lie between Re61 and 62 for Ri=l and between Re90 and 91 for Ri=2.