Numerical investigations on solid-fueled ramjet inlet thermodynamic properties effects on generating self-sustained combustion instability

Abstract

In this work, combustion instability of the solid-fueled ramjet (involving diffusion-dominant combustion process) is investigated using a numerical model. Effects of inlet thermodynamic properties, such as inlet temperature Tin, Mach number Ma and mass flow rate m˙a on generating combustion instability are evaluated. The 2-dimensional (2D) model is first validated with 3-dimensional (3D) model and the experimental data. Further validations are conducted on chemical reaction model, heat transfer model and diffusion models and comparing the acoustic signature of a Ramjet combustor and mode-shapes with the experimental data available. It is then used to identify stable and unstable acoustic modes exited by unsteady heat release in the combustor. Large-scale temperature waves are observed to be convected downstream. To clarify the mechanism of such limit cycles, Rayleigh criterion is utilized by analyzing the phase difference between the acoustic pressure and unsteady heat release rate. In addition, attempts are made to determine Rayleigh index and the oscillations' growth rate. Finally, it is found that the inlet temperature plays little roles on affecting the limit cycle intensity. This is quite different from m˙a and Ma. Larger m˙a and/or Ma, more intensified limit cycle oscillations. In general, the model provides a useful low-computational-cost numerical platform to investigate thermoacoustic instability in a Ramjet combustor.