Application of multiphase flows in combustion

The reacting multiphase flows such as the synthesis of aerosols in turbulent flames and reacting spray flows involve coupled, three-way interactions between turbulence, chemistry, and particle/droplet dynamics. Lagrangian methods in large eddy simulation (LES) concept are commonly adopted for computational modelling of such flows which are relevant to a wide range of engineering applications. The Lagrangian methods track the evolution of discrete elements in the turbulent gaseous phase. Suitable closures are required to model the complex multiscale and multi-physics interactions between the continues and disperse phases. In reacting spray flows, the effect of inertia is important. In such flows, the Lagrangian methods (known also as parcel methods) can be derived from either a deterministic or stochastic points of view where the stochastic method solves the transport equation of probability density function (PDF) of the number of droplets in a Monte Carlo scheme. Different models are adopted for droplet’s dispersion, evaporation, breakup, and particle formation in reacting turbulent flows. Two-phase flow models have also been developed based on the population balance equation (PBE) that governs the evolution of the number density which is a function of particle size, shape, morphology, etc. Various approaches including the methods of moment and Monte Carlo methods have been used to solve the PBE. Key challenges in modelling such flows are closure for particle agglomeration, nucleation, and growth which are nonlinear functions of environmental parameters.