One-Dimensional Combustion Instability Studies with Moving Boundaries in an End-Burning Test Motor

Abstract

A quasi-steady one-dimensional arbitrary moving boundary code is progressively developed for the objective of solving; full transient, moving boundary, rocket motor internal flow field problem. In this analysis, the propellant surface is modeled as moving, contrary to the common approach that assumes a stationary propellantburning surface. A one-dimensional Godunov type exact Riemann Solver is developed that can handle the boundary conditions for advancing and retarding walls. Moving propellant boundaries are handled with fixed grid approach by clipping the boundary inside grid points. The classical time-dependent inflow/outflow characteristic boundary conditions are implemented for exhaust. The mass injected from the propellant surface is modeled as the mass generated inside the control volume, represented in the source terms of the Euler equations. The resulting code is verified for moving boundary test cases, nozzle type geometries, and small test motors. Finally solid propellant combustion instability prediction capability is searched for an end-burning test motor configuration by comparing different burn rate models. Both steady state burning rate and a transient burning rate law is applied as a boundary condition. Acoustic oscillations at different frequencies are observed during the operation time. The pulsed oscillations occurred in higher modes. Results are discussed for fast and slow regression rates, long motors and steady state pressure levels. Frequency analysis of the flow variables and burning rate variations are done real time during the computations using non-stationary data analysis techniques. Pressure response function of the model propellant is assumed known from experiments available from the literature.