Active Instability Suppression Using Vortex-Droplet Interaction

Active instability suppression was demonstrated in an axisymmetric dump combustor which developed self-sustained oscillations under certain conditions. The control strategy was based on pulsed liquid-fuel injection whose frequency and timing were controlled actively. Both open- and closed-loop controls were demonstrated with and without a simple feedback loop. For open-loop control that runs without feedback, the injection frequency was changed shifting the operating regime to more benign conditions. In closed-loop control, only the fuel injection timing was adjusted in relation to the pressure oscillation phase. This affected the degree of interaction between injected droplets and large-scale periodic features of the flow, since the initial slip velocity was a function of the injection timing. The resulting change in spatial and temporal distributions of fuel droplets made it possible to manipulate the phase of local heat release oscillations and affected the amplitude of pressure oscillations. Up to 15 dB reduction in sound pressure level was observed with the present control approach.