Flow and thrust characteristics of rectangular expansion-deflection nozzles

To enhance the thrust performance of single-stage-to-orbit (SSTO) vehicle nozzles across wide nozzle pressure ratio (NPR) ranges while mitigating thrust degradation in annular expansion-deflection nozzles under low NPR conditions, a systematic investigation was conducted on the flow characteristics of rectangular expansion-deflection nozzles (REDNs). Numerical and experimental methods were used to investigate the flow field of the REDN under different NPR conditions and demonstrate the altitude compensation mechanism of the nozzle. The results indicate that the main factors affecting the thrust and flow characteristics of the REDN are the external airflow entering the nozzle at low-NPR conditions and the mode transition process. A higher external airflow rate into the nozzle results in a higher thrust, whereas an early mode transition reduces the thrust performance. The designed REDN has a thrust coefficient of 0.913 at NPR = 10 and 0.962 at the designed state NPR = 288.667. In addition, the thrust coefficients of the designed REDN are higher than 0.88 in the NPR range of 10-530. The effects of nozzle width and pintle sidewall deflection angle on the performance are further investigated. The results show that the nozzle width affects the NPR at which the mode transition occurs and the unit flow rate of the external air entering the nozzle. The deflection angle of the pintle sidewall has a significant influence on the operating mode of the nozzle. With excellent thrust performance over the wide range of NPRs, the REDN demonstrates the potential for application on an SSTO vehicle.