Author(s): Adrian Wing-Keung Law; Jiao Jian Ai; S. C. M. Yu
Linked Author(s): Adrian Wing Keung Law
Keywords: Boussinesq starting forced plume; Penetration rate; Vortex dynamics
Abstract: The characteristics of Boussinesq starting forced plumes were investigated in this study. Two distinct zones in the transient plume penetration were identified, namely the Zone of Flow Development (ZFD) and Zone of Developed Flow (ZDF). ZFD refers to the near source region whereby the penetration rate is governed by the complex vortex dynamics initiated by the exit conditions that can include vortex coalescence, vortex leapfrogging, pinching off of the head vortex from the trailing stem and the eventual reconnection. The pinch-off and reconnection leads to an overshoot of the plume front which is a common observation reported in previous studies. The penetration rate in ZDF is more predictable and depends on the continuous feeding of buoyancy and momentum into the head vortex by the trailing buoyant-jet stem. Similarity solutions are developed for ZDF to describe the temporal variation of the penetration rate, by incorporating the behavior of an isolated buoyant vortex ring and recent laboratory results on the trailing buoyant jet. In particular, the variations of velocity ratios between the head vortex and trailing buoyant jet are computed. To verify the similarity solutions, experiments were conducted on vertical starting forced plumes using planar laser induced fluorescence (PLIF).