Research Information System
Journal of Propulsion and Power, vol.37, no.5, pp.780-791, 2021 (SCI-Expanded)
Experiments have been carried out to investigate the effect of cowl length variation on performance characteristics
of a single expansion ramp nozzle. The performance parameters were estimated for cowl lengths of 0, 25, 50, 75, and
100% with respect to the horizontal length of the ramp. Experiments were conducted for different nozzle pressure
ratios ranging between 1.5 and 9. The wall static pressure distribution data were measured from the tests to estimate
the various performance parameters, such as axial thrust, normal force, gross thrust, thrust vectoring angle, and
coefficient of pitching moment. High-speed schlieren imaging was used to visualize the flow separation and shock
patterns and to measure the jet width. The flow was separated from the ramp wall up to a nozzle pressure ratio of 3 for
all cowl cases. The shorter cowl length delays the downstream movement of shock-induced boundary separation
inside the nozzle as compared to the longer cowl. The cowl trailing-edge flow was more underexpanded than the ramp
tip flow. As cowl length increases, the increased restriction results in higher axial thrust and also increases the normal
force. The pitching moment and thrust vectoring were dominated by normal force. Overall, as the nozzle pressure
ratio increases, the axial force and jet width increase, whereas the normal force and the pitching moment increase up
to a certain level and then decrease. As the cowl length increases, the axial thrust, normal thrust, pitching moment, and
thrust vector angle increase, while the jet width decreases.