Supersonic jet control with shifted tabs

Mixing characteristics of a Mach 2 jet controlled by shifted tabs have been studied at different levels of expansion at the nozzle exit. Two identical rectangular flat tabs of aspect ratios (length/width) 3, 4, 5 and 6, offering 2.5% blockage each, located diametrically opposite, found that the mixing promotion caused by the shifted tab increases with increase of adverse pressure gradient (that is, below NPR 5). On the contrary, the mixing enhancement caused by tab placed at the nozzle exit decreases with increase of adverse pressure gradient. At higher NPRs from 5 to 8 for shifted tab configuration, the amplitude of centerline pitot pressure oscillation is considerably smaller than the uncontrolled jet. At lower NPRs, corresponding to expansion level p(e) /p(a,) from 0.383 to 0.511, shifted tab is found to be a better mixing promoter than the tab at the nozzle exit. But for expansion levels from 0.511 to 1.022, mixing promoted by tab at nozzle exit is better than the shifted tabs. Shifted tab at 0.5D results in about 55% reduction in core length, at NPR 3, and the corresponding core length reduction by tabs at 0.25D, 0.5D, and 0D is 25.93%, 22.2%, and 14.81%, respectively.