Rectangular Sonic Jet Control with Supersonic Fluidic Injectors

Numerical simulation of an underexpanded rectangular sonic jet controlled with a pair of normally injected supersonic minijets on mixing promotion was carried out using a commercial computational fluid dynamics (CFD) solver. Results from three-dimensional (3D) Reynold’s-averaged Navier Stokes simulations exhibited very good agreement with experimental results for all the cases studied. Detailed analysis was carried out to quantify the influence of mass flow rate ratio and orientation of the air-tab injected along minor axis and diagonal axis, and pressure gradient at nozzle exit on the jet mixing. Centerline Mach number decay, density gradient contours, generation and propagation of streamwise vortices, axis switching, average shear layer thickness, and mass entrainment are used to quantify the jet mixing. It was found that fluidic injection along diagonal axis generates asymmetrical counter-rotating streamwise vortices causing rapid jet spread along the minor axis, resulting in axis switching and enhanced mass entrainment, leading to a shorter core and rapid characteristic decay. Although injection along the minor axis is capable of reducing shock strength, the decay caused by it is only marginal. Effectiveness of the fluidic injection diminishes with increases in the favorable pressure gradient. A maximum of about 53% reduction in jet core length was caused by injection along diagonal (IAD), corresponding to a mass flow rate ratio of 4%.