Computations of axisymmetric plug-nozzle flowfields: Flow structures and thrust performance

Plug-nozzle flowfields are analyzed by the numerical simulations. The method of characteristics is used to design the plug contour, and several types of plug nozzles are considered by truncating the length of the nozzle at different positions. Plug-nozzles' altitude-compensating features are confirmed by the computed results, and the base pressure turns out to play an important role to maintain the thrust performance of the nozzle for high-truncation configurations. The altitude clearly influences the base-pressure distributions under the assumption that the chamber pressure is constant during the ascent. The computed thrust difference between the contoured and the conical nozzle linearly increased as a function of the pressure ratio. The thrust performance of the contoured plug nozzle is estimated to be about 5-6% higher than the conical plug nozzle. Various conditions of external flows over the plug nozzle are also imposed, and the result shows that the external flow does not influence the pressure distribution on the nozzle surface for the pressure ratios higher than the designed point.