Large eddy simulation of effects of primary rocket jet on low frequency combustion instability in a RBCC combustor

This paper reports on effects of primary rocket jet parameters, which are among the most probable sources of combustion instability in a Rocket-Based Combined-Cycle (RBCC) engine, on combustion characteristics of a RBCC combustor numerically. Compressible Large Eddy Simulation (LES) with kerosene sprayed and vaporized is performed on an experimental RBCC combustor. Coupling with a reduced three-step chemical kinetics of kerosene, the LES is used to investigate the large amplitude and low frequency longitudinal oscillations in the engine. LES results are compared with experimental observations in pressure oscillation amplitude and frequency in the low components, all show good agreement. Influence of the primary rocket jet on pressure oscillations of the combustor is analyzed and the relation of its high speed jet oscillation characteristics with that of the combustor is recognized. Results reveal that the unsteady high temperature jet comes out of the rocket, which is always rich in fuel, has a significant influence on the vaporization and combustion features of the fuel downstream of the secondary fuel struts, and consequently on combustion features of the combustor. LES solver is validated with experimental data for a model scramjet located in the Institute for Chemical Propulsion of the German Aerospace Centre (DLR) and shows good predictions.