Study on the development of a laminar buoyant starting plume following a thermal

Abstract

Direct numerical simulations are conducted to study the dynamics of a laminar forced plume with sudden removal of the momentum source. The pinch-off process dependent on two non-dimensional parameters (Richardson number and injection duration) is analyzed, and the effects of the two parameters on the catching time when the pure plume catches up with the thermal ahead and the corresponding catching height are investigated. Four stages of the flow development, i.e., initial accelerating stage, transition and pinch-off stage, approaching stage, and interaction stage, are observed. It is found that with the Richardson number increasing, the thermal cap ascends to a higher height and the temperature near the heat source becomes lower. The increase of the Richardson number can cause the accumulation of heat beneath the thinnest stem, and the increase of injection duration can accelerate the accumulation of heat in the stem. It is observed that the fresh pure plume may catch up with the thermal ahead. The increase of injection duration can cause the increase of the catching time and catching height, while the increase of the Richardson number leads to the decrease of the catching time for a short injection duration.