The role of disordered dynamics on the nature of transition in a turbulent reactive flow system

Abstract: The transition from a chaotic to a periodic oscillatory state can be smooth or abrupt in real-world turbulent systems. Although there have been several mathematical studies, the occurrence of abrupt transitions in real-world systems such as turbulent reactive flow systems is not well understood. A turbulent reactive flow system consists of the flame, the acoustic field, and the hydrodynamic field interacting nonlinearly. Generally, as the Reynolds number is increased, a laminar flow becomes turbulent, and the range of time scales associated with the flow broadens. Yet, as the Reynolds number is increased in a turbulent reactive flow system, a single dominant time scale emerges in the acoustic pressure oscillations, indicated by its loss of multifractality. For such smooth and abrupt transitions from chaos to order, we study the evolution of correlated and uncorrelated dynamics between the acoustic pressure and the heat release rate oscillations in the spatiotemporal domain of the turbulent reactive system. The correlated dynamics that add or remove energy from the acoustic field are defined as conformists and contrarians, respectively. The uncorrelated dynamics, neither adds nor removes energy is defined as disorder. Conformist dynamics dominate the contrarian dynamics as order emerges from chaos. We discover that the spatial extent of the disordered dynamics plays a critical role in deciding the nature of the transition. During the smooth transition, we observe a significant presence of disordered dynamics in the spatial domain. In contrast, abrupt transitions are accompanied by the disappearance of disordered dynamics from the spatial domain.