Effect of Tab Parameters on Near-Field Jet Plume Development

A full understanding of jet mixing behavior is essential in the aircraft design process, particularly when propulsion system integration issues are considered (for example, jet afterbody interactions, jet plume characterization, and jet noise reduction). The present work is motivated by an interest in unconventional jet exhaust nozzle design, specifically tabbed nozzles. The near-field mixing performance arising from a simple axisymetric jet shear layer and three-dimensional perturbed jet shear layers created via a range of solid tab designs introduced at the nozzle exit plane has been studied under subsonic and supersonic operating conditions. The effects of velocity ratio, tab shape, tab number, and tab orientation angle are investigated. Flow visualization of the tab effects is accomplished via laser-induced fluorescence in low-speed flow and schlieren imaging under supersonic conditions. The mean and rms axial velocity as well as pitot pressure and total temperature profiles have been measured along the jet centerline and on orthogonal cruciform radial traverse lines downstream of the nozzle exit. The performance of the solid tab in causing bifurcation of the jet was found to follow the same trend under both subsonic and supersonic conditions, indicating that the dominant features of the streamwise vorticity introduced by the tabs are essentially independent of the Mach number. The experimental results revealed that the decay of the jet core velocity was only weakly dependent on velocity ratio (over the range studied here), tab orientation angle, and tab shape. The mixing of the jet was, however, a strong function of the tab projected area, tab width, and tab number. The optimum tab number was found to be 2.