Entrainment characteristics of a swirling liquid jet plunging in a quiescent pool of liquid

We have explored the entrainment characteristics of a swirling liquid jet plunging into a quiescent liquid pool. We carried out three-dimensional simulations for a range of swirl parameters $0.5\le S\le 1.6$ and axial Reynolds number of $4000\le Re\le 12000$. The main objective of the current investigation is to explore the impact of the swirl parameter on the entrainment characteristics of a swirling plunging jet. The results indicate that the air volume consistently increases up to a swirl parameter of $S=1.2$, beyond which it decreases for a fixed Reynolds number. The amount of air being entrained depends upon the trade-off between the axial inertia in competition with radial inertia and buoyancy. We have delineated the mechanism of transition through turbulent kinetic energy possessed by the swirling liquid jet for the range of swirl parameters considered. Further, the bubble penetration depth decreases with increasing swirl parameters. We also identified the breakup morphology of the initial air-cavity pinching-off into smaller air bubbles for the case of swirling plunging jets and compared it with their non-rotating counterpart.