Response of soot formation to fuel inlet perturbation in an aero-engine model combustor

Soot formation and evolution are highly sensitive to fuel inlet perturbations, especially in confined turbulent swirling flows, where complex flow dynamics can amplify the impact of the perturbations. In this context, it is essential to quantitatively analyze the sensitivity of soot evolution to the perturbation. To this end, large-eddy simulations with system identification (LES/SI) of an aero-engine model combustor are conducted with state-of-the-art soot models. The sooting swirl flames are modelled as a single-input single-output (SISO) system. Similar to the flame transfer function F, a soot transfer function S is defined to characterise the response of soot to the inflow perturbation. The results show that for sufficiently small perturbations, the system can be assumed to be linear and time-invariant, and hence both F and S can be obtained from the unit impulse response (UIR) by a z-transform. Furthermore, it is found that S exhibits large amplitudes in the low-frequency band (22–150 Hz) and has negligible amplitude after exceeding 400 Hz that corresponds to the characteristic frequency of precessing vortex core (PVC). On the other hand, F exhibits three amplitude extrema at 400 Hz, 800 Hz, and 1200 Hz, respectively. Compared to flame response delay, soot response delay is very sensitive to the perturbation frequency. This work presents an opportunity to investigate soot from a nonlinear dynamics perspective.