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The attitude control of a rocket engine using the control surfaces becomes cumbersome particularly in larger rockets with high payload. In such cases, a more effective means of producing forces for controlling the flight is the deflection of exhaust gases, referred to as the gas-dynamic steering or the thrust vector control. In this study, the effect of a strut on the exhaust gas deflection, deployed at the locations; 0.62 L, 0.72 L and 0.8 L in the divergent-portion of a Mach 1.84 nozzle at over-expanded, correctly-expanded and under-expanded states of the jet, has been experimentally investigated. The level of expansion at the nozzle exit is varied by changing the settling chamber pressures from 4 bar to 8 bar, in steps of 2 bar. Further, to study the effect of aspect ratio, the height of strut is varied as 1.5 mm, 2.5 mm and 3.5 mm. The strut of height 3.5 mm, deployed at x/L = 0.72, is found to be the most effective thrust vector control at overexpanded conditions; with a maximum jet deflection of about 3.6 o , obtained at a settling chamber pressure of 4 bar. The Schlieren flow visualization images confirm the findings of wall static pressure data.

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To improve the stealth capability of a military aircraft, the reduction in core length is essential to reduce the heat signature and the noise characteristics of the engine exhaust. The efficacy of rectangular vortex generators in achieving these objectives has been demonstrated by several researchers, owing to their simplicity. One way of producing the mixed-size vortices is by providing corrugations on the edge of the tab (actuator). Therefore, in the current study, two tabs of aspect ratio 1.5, mounted diametrically opposite to each other at the outlet of a Mach 1.73 circular nozzle, are examined at varying levels of expansions, ranging from overexpanded to underexpanded jet states. In addition, to generate the mixed-size vortices, three corrugation geometries, i.e., rectangular, triangular, and semicircular, are configured along the tab edges. Both quantitative and qualitative investigations are carried out by using the pitot probe to measure the stagnation pressures and by utilizing a shadowgraph technique to visualize the flow field. The corrugated tabs generated a significant mixing, and among them, the tabs with triangular corrugations are found to be most effective. A maximum reduction of about 99.7% in the supersonic core is obtained with triangular corrugated tabs at near-correct-expansion, corresponding to nozzle pressure ratio (NPR) 5. Interestingly, the semicircular corrugated tab significantly reduces the asymmetry near the nozzle exit plane. The shadowgraph images confirm the efficacy of different corrugated tabs in reducing the strength of the waves, prevalent in the supersonic core.

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