In this paper, we present a detailed and novel analysis of the mitigation mechanism of instability in a lean premixed, swirl-stabilized, labscale combustor by actuating the swirler. It has been reported in our previous work that increasing the swirler rotation rate mitigates the self-excited thermo-acoustic instability in a model lab-scale combustor, over a range of conditions. Here, it is found that for a given period of observation, instead of a continuous and gradual decrease in the time localized pressure amplitude from the fully unstable state towards the fully mitigated state, the fraction of the time during which instability is present is reduced. With increasing swirler rotation rates, the instability becomes more bursty and its frequency decreases progressively. Such an intermittent route to instability mitigation could be attributed to the background turbulent flow field and is reminiscent of the intermittent opposite transition (implemented by changing the Reynolds number) from a fully chaotic state to a fully unstable state as recently discovered in Nair et al.[1]. An attempt is made to model the behavior of pressure oscillations using the well-established mean-field Kuramoto model. The variation of the order parameter r, which measures synchronization of the oscillators provides critical insights on the transition from the unstable, intermittent to stable states.
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