Simulation of thermo-acoustic instabilities including mean flow effects in the time domain

Thermo-acoustic instabilities may arise in various technical combustion systems, such as industrial and household burners, gas turbines, afterburners or rocket engines. These self-excited oscillations originate from the interaction of combustor acoustics and flame dynamics. To predict their occurrence it is necessary to describe the interaction between the propagation of acoustic perturbations, flame behaviour and acoustic losses correctly. Most methods for calculating thermo-acoustic instabilities suffer from a high degree of simplification. Mean flow effects are usually completely neglected. A new approach for the simulation of combustion instabilities in the time domain including mean flow effects is presented. The basic idea of the method is to solve the unsteady linearised governing equations for a three-dimensional combustor geometry. A rocket engine where mean flow effects are particularly strong is used as example. It is shown that this method delivers promising results that do not require the use of nozzle admittances. The differences in oscillation amplitudes with and without consideration of the mean flow are highlighted.