COMPUTATIONAL STUDY OF MIXED CONVECTION EFFECTS ON THE FLUID FLOW FORCES ON A ROTARY OSCILLATING CIRCULAR CYLINDER

Numerical experiments are performed to study the effects of thermal buoyancy force on the heat transfer characteris-tics of fluid flow around a rotary oscillating cylinder. The flow and thermal fields are characterized by the oscillation frequency and amplitude and the Richardson number (Ri). The instantaneous and time-averaged lift and drag force coefficients (CL and CD) as well as Nusselt number (Nu) are calculated in lock-on and non-lock-on flow states. A ther-mophysical influence upwind scheme is developed for a control volume finite element method (CVFEM) to incorporate buoyancy force in estimation of flow variables at control surfaces. The numerical results indicate the prominent effect of thermal buoyancy force on the onset of the lock-on flow state at an oscillation frequency and amplitude. Variation of oscillation frequency and amplitude shows different influences on the heat transfer characteristics in the lock-on and non-lock-on flow region. In the non-lock-on flow region, as the oscillation amplitude increases, maximum lift coefficient and average drag coefficient increases while the Nusselt number decreases. The vortex convection in the wake region is suppressed by thermal buoyancy force opposite to the incoming flow, resulting in a decrease in the time-averaged Nusselt number.