Abstract
In trapped vortex combustor (TVCs), where a cavity is used for flame stabilisation, large-amplitude periodic pressure fluctuations can occur at certain operating conditions due to flow-acoustics lock-in. In the present study, experiments were carried out in a laboratory-scale trapped vortex combustor by varying cavity sizes (L/D = 0.75–2.65). Unsteady pressure measurements reveal a bifurcation route of limit cycle → steeper limit cycle (with higher harmonics) → quasi-periodic → strange non-chaotic attractors (SNAs) → chaos as cavity size is increased (L/D). This overall transition leads to a 70% reduction in pressure amplitude and as such can be treated as a passive control strategy to mitigate unwanted oscillations. We employ a reduced-order model that incorporates this flow-acoustic lock-in. This model includes a feedback mechanism that accounts for the influence of acoustic modes on the vortex-shedding event. This feedback mechanism induces changes in the timescale of vortex impingement as cavity size varies, leading the system through the experimentally observed non-linear regimes. We validate our model by comparing its predictions with experimental results, highlighting its ability to capture the intricate dynamics observed in cavity-based combustors.
