NUMERICAL STUDY OF SCRAM ACCELERATOR STARTING CHARACTERISTICS

A numerical study is carried out to investigate the ignition and the d etonation initiation process in a scram accelerator operating at a sup erdetonative mode. To simulate the scram accelerator launching process , a conical projectile is considered, injected with an initial velocit y of 2500 m/s from the 1 atm air into a 25 atm 2H(2) + O-2 + mN(2) mix ture. As a dilution gas, nitrogen is selected and assumed to be inert. The time accurate solutions of Reynolds averaged Navier-Stokes equati ons for chemically reacting flows are obtained by using a point-implic it method and an upwind-biased third-order scheme with a steady-state solution for airflow as an initial condition. To examine combustion ch aracteristics and ram-accelerator operation limits, mixture compositio ns are varied from 2H(2) + O-2 + 3.76N(2) to 2H(2) + O-2 + 9N(2) by ch anging the amount of N-2. The flowfield results show the detailed igni tion mechanism, the initiation process of the oblique detonation, and the starting characteristics of the scram accelerator. The results als o identify clearly the combustion characteristics of the operational f ailures at tower and upper dilution limits that have been observed in experiments. The visualized flow results of the present simulation pro vide a better understanding of the supersonic reacting how in a scram accelerator.