Control authority over a combustion instability investigated in CFD

Control authority is investigated for active damping of a combustion instability by modulation of the fuel flow. Two combustors, operating as quarter-wave thermo-acoustic oscillators, are modelled in ANSYS CFX. In experiments, active damping was applied successfully on one of these, but was not effective on the other. Active instability control is implemented in the model analogous to experiment. The goal of this research is to explain why the same implementation of active instability control, using the same controller, would be effective on one combustor geometry, but not on the other. Turbulent combustion is modelled by SAS-SST and the burning velocity model. The distribution of the convective time between fuel injector and flame is evaluated and used to estimate the response of the heat release to modulation of the fuel mass flow. The results can be used to predict the feasibility of this kind of active control.