Impact of secondary flow parameters on thrust performance of an annular air inlet nozzle

The influence of operating altitude and annular inlet mass flow on the thrust performance of an annular air inlet nozzle was investigated through numerical simulation methods to analyze the working process of the nozzle. Based on an analytical strategy of dividing the airflow inside the nozzle into primary combustion gas and secondary flow for separate investigation， the flow characteristics of the airflow in the annular air inlet nozzle were obtained. The influence of different inlet mass flow on thrust performance at various operating altitudes was explored. The results show that under the synergistic effect of the convergent and divergent accelerating flow channel and the intensified expansion zone as well as the speed transition zone， the secondary flow expand and accelerate in the nozzle， and when the secondary inlet mass flow varies from 1 to 75 kg/s， the nozzle has additional dynamic thrust of 5.1%，6.1%， 4.3% at 5 ，10， 15 km operating altitude， respectively， so that the specific impulse has an increase of 4.3%，4%，and 3.7%， correspondingly. Below the altitude of 10 km，the inlet mass flow and thrust performance of the annular air inlet nozzle has a positive relationship； at the altitude of 10~20 km， optimal thrust performance can be achieved when the inlet mass flow is 15%~20% of mainstream gas flow； and above the altitude of 30 km， the inlet mass flow and thrust performance of the annular air inlet nozzle has a negative relationship. The results suggest that the advantage of annular air inlet nozzle can be mainly achieved at low altitude.