EFFECTS OF BUOYANCY ON THE TURBULENT WAKE OF A HORIZONTAL CYLINDER IN CROSS-FLOW

摘要

While heat transfer around bluff-bodies have been extensively studied in natural and forced convection regime, the mixed convection regime has not still yet brought so much attention ; however the latter has direct interest either in various engineering applications or for fundamental point of views. Direct Numerical Simulation was applied in this paper to study the buoyancy effects in the wake of a horizontal cylinder in cross-flow for Re_∞=1000 and Ri=2.77. In the framework of mixed convection regime, results mainly focus on the role of thermal field and buoyancy effects. The main visible impact in the thermal field introduction is the asymmetry in the cylinder wake. In addition, typical mushroom-like structures driven by thermal field develop along the wake. From an unsteady point of view, a thermal wave develops from the bottom of the cylinder and the latter follows the cylinder surface. As a consequence, the upper shear-layer that occurs in isotherm case is strongly disturbed because of the interaction with the thermal wave and the lower shear-layer is stretched in the flow direction. Comparisons with the isotherm case help us to better understand the role of the thermal field and the effects of buoyancy in the transition to turbulence.