Near field entrainment characteristics and recirculation zones in a swirling liquid jet

Entrainment and mixing are desirable in many industrial applications involving chemical reactors and combustion chambers. Here, we explored the near-field entrainment characteristics in a swirling liquid jet injected into an ambient gaseous phase. We have carried out three-dimensional numerical simulations using the open-source code Gerris for a wide range of swirl numbers 0.5≤S≤1.55 and Reynolds number range of 50≤Re≤300. The main objectives of the present work are to understand the near field entrainment characteristics of the swirling jet and the development of recirculation zones in the ambient air. The results indicate that, the entrainment is enhanced at higher swirl strength for a constant Reynolds number. The maximum entrainment has been found to occur at the shear layer between the swirling liquid jet and ambient air. Also, multiple recirculation zones develops outside the liquid vortex core which facilitates better mixing in the flow. It is also observed that the ambient air experiences a toroidal recirculation in the flow field, which leads to shearing and breakup of the liquid-air interface. Furthermore, we have also computed the entrainment coefficient (C_e) which varies from 0 to 0.15. These entrainment coefficients are comparable to the entrainment coefficients obtained for thermal plumes but lesser than the entrainment coefficients observed for free turbulent jets and plunging jets.