Spatiotemporal information propagation in confined supersonic reacting flows

The interplay between mass injection, heat release, and boundary layer development plays a key role in dictating the dynamics and stability of confined supersonic flows. The relative impacts of these factors and the timescales over which they influence the upstream and downstream flow can provide critical insights into how different operating modes develop. As such, this work presents a series of simulations of an experimental axisymmetric direct connect flowpath. The mass flow rates and chemical compositions of the injection stages are varied, and subsequent information propagation and mode transitions are analyzed using spatiotemporal correlations of cross-sectional averaged quantities. Increasing the injection flow rate decreases the time lags and durations of positive correlations between pressure and heat release at various points along the flowpath. Meanwhile, in dual-mode cases with lower injection flow rates, these correlations develop after longer time delays and persist for a longer times, illustrating how information propagates more gradually in these scenarios. Over the full flowpath, positive correlations persist for comparatively long times between (1) the upstream isolator pressure and the pressure elsewhere, and (2) the pressure in the downstream diverging combustor section and the upstream pressure. As such, the influence of the pressure in the intermediate constant-area combustor section decays more rapidly. Conditional statistics suggest that flow blockage and pressurization from the injected mass reduce the local ignition delay, thereby facilitating increased pressurization via heat release in a positive feedback loop.