Experimental Investigation of Elliptic Jet Control using Airtabs

Abstract

An elliptical nozzle (the aspect ratio AR is equal to 2) with an equivalent diameter of 10 mm is experimentally investigated at the Mach number M = 0.4 with the secondary fluidic injection of M = 0.6 minijets with four air tabs placed diametrically opposite to another at the nozzle exit plane. The high-speed jet facility is used to characterize the jet behaviour of the manipulated jet with the uncontrolled open jet. The effects of the minijet mass flow rate and the diameter ratio (air tab diameter/nozzle exit diameter) are analysed. In this experimental investigation four air tabs of 0.4, 0.5, 1 mm diameters being placed at the elliptical convergent nozzle exit at 90° to each another. As distinct from the circular nozzle, non-uniform vortices may be generated from the larger and shorter curvature of the major and minor axis of the elliptical nozzle, thus increasing the mass entrainment from the ambient to the main jet core. Air tabs not only generating the streamwise vortices and also induces Kelvin–Helmholtz instability due to the momentum difference in the primary jet due to the secondary jet thus promoting the mixing which reflects in the rapid reduction in pressure in the potential core region of the jet. Compared to the uncontrolled jet, the percentage of reduction in potential core is obtained as 40, 45, and 80% with the 0.4, 0.5 and 1 mm air tabs, respectively. Also, from the radial profile, a significant jet distortion is observed due to the amount of the energy added in the primary jet and the penetration of the secondary jets which is more significant in the minor axis as compared to the major axis of the elliptical nozzle. From the pressure plots and the analytical investigation, it is documented that 1 mm air tabs which sustain more momentum flux thus enhancing the entrainment ratio to the primary jet as compare to the 0.4 and 0.5 mm air tabs-controlled jets.