RESEARCH OF SUPERSONIC FLOW IN SHORTENED NOZZLES OF ROCKET ENGINES WITH A BELL-SHAPED TIP

Abstract

The flow in a shortened nozzle with a bell-shaped tip is considered. A comparison of the wave structures of the supersonic gas flow in shortened nozzles with short and long tips formed by compression and stretching of the original bell-shaped nozzle for connection, respectively, with the long and short conical part of the base nozzle at the same nozzle length was carried out. Under operation conditions at sea level and low pressure at the nozzle inlet (P0<50·105 Ра), a large-scale vortex structure, starting from the corner point of the nozzle inlet, is observed in both nozzles. In addition, in the long tip, a small-scale vortex is observed on the wall near its cut. A barrel-shaped wave structure of hanging jumps with a closing Mach disc is formed in the flow in both nozzles, inside which a "saddle-shaped" wave structure of low intensity is noticed. In the separation flow in the tip (when Р0<50·105 Ра and Рн = 1·105 Ра), the pressure on the wall in the separation zone is slightly lower (by ≈ 5-10%) than the external pressure Рн. When the engine is operating in the upper layers of the atmosphere, the static pressure on the section of both tips is proportional to the pressure at the entrance of the nozzle. In the cross-section, starting from the axis of the nozzle to ~0.89 R/Ra (the ratio of the current value of the radius R to the radius of the nozzle wall at the outlet Ra), the pressure decreases to a value proportional to the pressure at the nozzle inlet. Then, it increases linearly to the value of the pressure on the tip wall, which is proportional to the pressure at the nozzle inlet. This is due to the wave structure of the flow inside the nozzle. It was established that with a decrease in the length of the nozzle conical part, the impulse coefficient of the nozzle decreases significantly for operating at sea level and slightly decreases for operating in the upper layers of the atmosphere. The results of calculations correlate satisfactorily with the experimental study results of the flows in shortened nozzles with a bell-shaped tip