Mechanism of momentum transportation in the intermediate wake of a heated cylinder

Abstract

Measurements in the wake of a heated cylinder are made by a thermo-anemometer. The purpose is to make clear the effects of buoyancy of heated cylinder on the mechanism of momentum transportation in the wake. In this work, the diameter of the cylinder is D=0.030 m, Reynolds numbers Re_D=U₀D/ν are 3000～10000, Δθ=0～225 K and Richardson number Ri_D=gβΔθD/U₀²=0～0.0568. The causes of antisymmetric configuration in the horizontal heated cylinder wake are the downward motion of the vortex streets in upstream sections, and in downstream sections, the upward stretching of upper side vortices due to buoyancy. The antisymmetric wake configuration, caused by heating, affects on the mechanism of momentum transportation. In the upstream sections, velocity fluctuation at the vortex shedding frequency f_c plays an important role in the momentum transportation, but in the downstream sections, the breakdown of the shedding vortices are accelerated by heating, and the main contribution to the momentum transportation supersedes by velocity fluctuations at frequencies lower than f_c.