Three dimensional reacting flow analysis of a cavity-based scramjet combustor

Rouzbar, Ramin
Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process. Combustion at high speeds cause various problems as flame instability and poor fuel-air mixing efficiency. One of the methods used to overcome these problems is to recess cavity in the combustor wall where secondary flow is generated. In this study, a CFD tool is developed to analyze the reacting flow passing through the cavity-based scramjet combustor. Developed CFD code is based on three dimensional coupled Navier-Stokes and finite rate chemistry equations. Ethylene-air reduced chemical reaction model is used as fuel-air combination. Non-dimensionalized governing equations are discretized by Finite Volume Method (FVM) and Newton GMRES method is used to solve the coupled system of equations. First and second order schemes are investigated with different flux vector splitting methods. Moreover, flux limiters are implemented to improve the convergence of the second order schemes. It is found that second order schemes and Van Leer flux vector splitting methods are more accurate. In order to remove the dependency of the solutions on grid resolution, mesh refinement is done. In addition, effect of various fuel injection angles and injector locations on the efficiency of the combustor are investigated. It is found that 90 degree fuel injection angle gives the best mixing efficiency while addition of downstream injectors do not contribute to the overall efficiency. To sum up, the fundamental aim of this study is to analyze the reacting flow through the scramjet combustor efficiently and also examine new methods to improve the performance of the combustor.