The interaction between turbulence, chemical kinetics and droplet dynamics plays an important role in reacting flows and can lead to instability. Understanding the underlying mechanisms that drive these processes is critical for predicting and controlling them, and may significantly enhance combustion efficiency which is a crucial design parameter for gas-turbines and propulsion systems.
In this talk, I will present results from theoretical and experimental studies of different reacting flow configurations. Employing large eddy simulations, we show that under lean premixed conditions the dynamic response of a turbulent reactive flow is strongly impacted by the fuel chemistry. In order to gain insight into some of the underlying mechanisms we formulate a new linear stability model that incorporates the impact of finite rate chemistry on the hydrodynamic stability of shear flows. In contrast to previous studies which typically assume that the velocity field is independent of the kinetic rates, temperature coupled mechanisms are accounted for through a variable density Navier-Stokes formulation. This formulation is shown to agree with results of our recent experimental and computational studies and suggests a physical explanation for the observed impact of finite rate chemistry on turbulent shear flow instability.
Adding particles and droplets to the reactive flow may alter its structure and stability. I will revisit Saffman’s seminal work on the stability of particle-laden flows, and present a new concept for the analysis of hydrodynamic stability of multiphase flows using the sectional approach. Preliminary results reveal the impact of droplet evaporation on the stability of the Hagen-Poiseuille flow. Remarkably, while the addition of non-evaporating particles tends to stabilize the flow, volatile droplets of the same size can destabilize the flow. This may also imply an earlier transition to turbulence in flows advecting volatile droplets.
