Vortex ring formation in starting forced plumes with negative and positive buoyancy

• DOI: 10.1063/1.4966648
• Publication Date: 2016-11-08T18:00:19Z
• Authors: L. Gao; S. C. M. Yu
• Keywords: Dimensionless quantity

The limiting process of vortex ring formation in starting forced plumes, with Richardson number the range −0.06 ≤ Ri 0.06, was studied numerically under Boussinesq approximation. examination dynamics flow evolution reveals that plume-ambient density difference affects pinch-off mainly through three mechanisms, i.e., baroclinic production vorticity, buoyancy acceleration (or deceleration) on vortical structures, and its effect trailing shear layer instability. As increases from negative to positive values, regimes can be identified terms interaction patterns during process, weak-interaction regime (−0.06 < − 0.02), transition (−0.02 0), strong-interaction (0 0.06). By eliminating influence vorticity production, circulation method proposed for jets is revised determine buoyant F plumes. Besides F, another dimensionless time scale (dubbed as separation S), which corresponds end by vanishment flux feeding leading ring. numerical results show variation trends against change near critical value Ric ≈ 0.02. In regime, both increase rapidly Ri. While alike, at a much slower rate than declines dramatically increases. Finally, qualitative explanation based effects dynamic properties patterns.