Rectangular jet with shear layer swirl: Rotation & mixing enhancement

Abstract

A rectangular jet emerging from a nozzle with embedded swirl vanes in its exit boundary layer is studied. The swirling shear layer imposes an external torque on the jet boundary where it causes jet rotation in the direction of axis switching, skew deformation as well as enhanced mixing. In moderate aspect ratio rectangular nozzles, e.g. AR = 5:1, a pair of co-rotating streamwise vortices is formed on the narrow boundary of the jet that dominates its dynamics in the near field. A vortex-induced model is developed that accounts for the rotation of the rectangular jet with embedded shear layer swirl. The model also shows that the jet rotation is diminished with increasing aspect ratio, as AR−2. The higher entrainment rate in the rotating jet with skew deformation causes the jet mass flow rate with shear layer swirl to be 20–25% higher than the corresponding plain rectangular nozzle of the same aspect ratio (x/De > 1). The proposed model is validated using computational simulation results of previous investigations that appeared in the literature.