Interaction of the acoustic oscillations of the combustion products in the chamber of a propulsion system with structural vibrations

The most critical operating conditions of propulsion system chambers are often due to the development of dynamic processes characterized by excess values of operational parameters. Pressure surges and a sharp increase in the local temperature of the combustion products may result in a structural failure of the combustion chamber and a critical behavior of the propulsion system, to the point of combustion termination. An approach was developed to solving problems of propulsion system dynamics – assessment of the effect of the acoustic oscillations of the combustion products in the chamber with account for their interaction with the solid-propellant propulsion system structure and for propellant oscillation and structural vibration damping on dynamic (acoustic) processes in the combustion chamber. The dynamic interaction of the operating process in solid-propellant propulsion systems with the spatial vibrations of the chamber structure was studied numerically. To get insight into its mechanism, the dynamic interaction between pressure oscillations and longitudinal structural vibrations was studied with adding a harmonic disturbance (~1 % of the thrust). It was shown that the dynamic coupling between the structural vibrations and the acoustic oscillations in the bulk of the combustion products should be taken into account in studying the strength of propulsion systems. This dynamic coupling manifests itself actively when the eigenfrequencies of the structural vibrations are close to those of the acoustic oscillations. It is shown that at some frequencies (depending on the phase relationships) the acoustic oscillations of the combustion chamber pressure may increase or decrease. Controlling this dynamic process with the aim to reduce the oscillation level for a certain flight time period calls for a further study of the effect of the following factors on these dynamic processes: the geometry of the combustion chamber, its operational conditions, and the presence of damping elements.