Modeling unsteady and perturbed combustion of heterogeneous composite propellants

The paper reports further developments of a numerical model for the combustion of composite solid propellants. Improvements include a better simulation of the fluid-dynamics by considering full Navier–Stokes equations coupled with species conservation, mass balance and energy balance equations. The model is also able to simulate the process under the action of an external perturbation, which is produced by a time-dependent heat flux impinging the propellant surface (e.g. laser source). Results of the model are reported in the paper in terms of two-dimensional distribution of most relevant variables, including gas concentration, velocity and temperature. The model has been validated against data of ignition delay available in the literature. The present study confirms that a simplified approach for fluid-dynamics is acceptable above a characteristic distance from the propellant surface, which is shortened at low values of the particle size and pressure. The analysis of model results under perturbed conditions demonstrates the pulsating impinging flux largely influences the propellant performance, the burning rate being largely increased by the irradiation. A periodic pulsating flux induces an oscillatory behavior of the burning process. At low perturbation frequency, the propellant is forced to burn at the same frequency of the external source. At high perturbation frequency, this effect disappears and typical fluctuations induced by the propellant heterogeneity are again evident. The transition between lower to higher frequencies (100–500 Hz) leads to emphasize the standard deviation of the observed time-dependent outputs (e.g. exit temperature), denoting the onset a resonance effect.