Manipulation of Supersonic Jet using Grooved Tabs

This study experimentally evaluated the mixing augmentation of twin tabs mounted along a diameter at the outlet of a convergent-divergent Mach 1.62 circular nozzle. The usefulness of the plain and grooved tabs is examined at various expansion levels prevailing at nozzle outlet. The tab's performance is assessed through pitot pressure distribution measured along and perpendicular to the jet centerline at different nozzle pressure ratios (NPRs). The shadowgraph technique visualized the shocks and expansion fans in uncontrolled and controlled jets. With the introduction of uncorrugated or plain tabs at the nozzle outlet operating under overexpanded conditions corresponding to NPR 4, the supersonic length (SL) was decreased only by 35.4%. On the other hand, the corrugated or grooved tabs under similar conditions decreased the SL substantially. Interestingly, the performance of grooved tabs was best at underexpanded conditions associated with NPR 6, where the SL was reduced by about 88%. The pressure profiles also established the superiority of tabs with grooved edges in mixing augmentation without introducing any significant asymmetry to the flow field. In addition, the Shadowgraph images also confirmed the weakening of shock strength and reduction of shock-cell length in the case of grooved tabs at the nozzle exit compared to the plain nozzle.