Numerical investigation of effect of buoyancy on the wake of a heated cylinder in contra flow

Flow over a cylinder is a classically and practically interesting problem. A number of studies focus on the vortex shedding and wake instability of an unheated cylinder. Inspite of its applications flow over a heated cylinder operating in a mixed convection region has received very little attention. The present study aims at the numerical investigation of unsteady heat transfer for a laminar flow past a circular cylinder with small aspect ratio (L/d=7) or finite spanwise length with no-slip wall conditions. A circular cylinder is exposed to approaching flow stream in the direction of gravity or opposing the direction of buoyant force (contra flow). The Reynolds number and the temperature of the incoming flow are set as Re=130 and 297 K respectively. The temperature of the heated cylinder is varied between 297 K to 358 K corresponding to Richardson number varying between Ri=0.0 and Ri=1.05. The analysis performed focuses on the effect of buoyancy on the wake instability in terms of vortex shedding frequency, drag forces, wake centerline velocities, averaged Nusselt number and transition phenomenon. In addition to this, preliminary study is conducted to understand the influence of small aspect ratio and end effects on the transition mechanism due to heating. Numerical results are compared to available experimental data and some new results are presented.