EFFECTS OF A CYLINDRICAL SOLID SHIELD ON THE ENTRAINMENT OF AMBIENT AIR INTO TURBULENT AND LAMINAR ARGON PLASMA JETS

摘要

Modeling study is conducted in this paper to reveal how the length of a coaxial cylindrical solid shield affects the air entrainment into the turbulent and laminar argon plasma jets. It is shown that the axially-decaying rates of plasma temperature, axial velocity and argon mass fraction in the turbulent plasma jet are much larger than their laminar counterparts, because the turbulent transport mechanism dominant in the turbulent jet is much more effective than the molecular transport mechanism in the laminar jet and thus much more air is entrained into the turbulent plasma jet. It is found that the solid shield can appreciably change the flow pattern in the region outside the plasma main-jet, but the plasma temperature, axial velocity and argon mass fraction distributions in the main jet region are less influenced by adding the solid shield. When a solid shield is added, a toroidal recirculation vortex appears near the corner between the shield wall and the torch rear-wall, and the axial size of the recirculation vortex appearing in the flow field lengthens with increasing shield length. However, the mass flow rate of the ambient air entrained into the plasma jet cannot be appreciably reduced by the solid shield.