Mixed convection around a circular cylinder in a buoyancy-opposing flow

Abstract

Numerical analysis of unsteady mixed convection about an unbounded heated circular cylinder placed in a downward vertical air-stream to study the influence of opposing thermal buoyancy on the flow behavior, skin friction, and heat transfer. For this purpose, the transient Navier–Stokes equations and the standard energy equation are solved numerically using the finite-volume method incorporated in our private house- code.  The investigation is carried out for Reynolds number of (Re = 10, 20, 30), and Richardson number of (Ri = 0 - 1), and at constant Prandtl number of (Pr = 0.71). The results, which are reported based on streamlines and isotherms, reveal that increasing the opposing buoyancy effect induces more flow instability in the upstream region, and produces twin counter-recirculating vortices. Also, it is revealed that this buoyancy effect increases both Nusselt number and the frictional coefficient. However, the increase in Reynolds number increases Nusselt number, but decreases the frictional coefficient.