Experimental Studies on Supersonic Jet Control Using Shifted Air Tabs

Abstract

Mixing of Mach 2.1 jet issuing from a straight convergent-divergent circular nozzle, in the presence of sonic air tabs at the exit and shifted locations along the jet axis was investigated experimentally at Nozzle Pressure Ratios (NPRs) 3 to 6, in steps of 1. Two constant area tubes of 1 mm diameter positioned diametrically opposite to each other, at 0D, 0.25D, 0.50D and 0.75D (where D is the nozzle exit diameter), were used for fluidic injection. The Injection Pressure Ratio (IPR) of air tabs was varied from 3 to 6 in steps of 1. The Mach 2.1 jet operated at NPR in the range of overexpanded states corresponding to NPR 3 6 was controlled with the sonic air tabs operating at the underexpanded state corresponding to 3 to 6. The impact of the Injection Pressure Ratio (IPR) and the location of air tabs on jet mixing was studied from the measured Pitot pressure along all three axes from the nozzle exit, particularly along the jet centerline (X-axis). The centerline decay of jets confirms that the air tab promotes jet mixing with the entrained air mass and the mixing promotion caused by the air tab is dependent on tab location, IPR as well as NPR. In the presence of air tabs, the jet possesses shorter core and experiences faster decay than the uncontrolled jet. Also, the air tabs were effective in reducing the number of shock cells and rendering the waves weaker in the jet core. Regarding the impact of IPR, the study found a consistent trend wherein increasing IPR led to a reduction in the core length of the jet. This reduction was observed across a range of NPRs from 3 to 6. The percentage reduction in core length becomes more pronounced as the IPRs increase for all NPRs.The maximum percentage reduction in core length was achieved at IPR 6 for all NPRs, when air tabs are positioned at the nozzle exit (0D) and 0.25D from the nozzle exit. Notably, the most significant reduction in core length occurred at IPR 6, indicating the critical role of higher pressure ratios in controlling jet behavior. However, it was observed