Inert-droplet and combustion effects on turbulence in a diluted diffusion flame

The inert-droplet and combustion effects on turbulence in a diluted diffusion flame are investigated using direct numerical simulation (DNS) through parametric study. The computational configuration is a temporally-developing reacting mixing layer laden with close to 17 × 106 inert evaporating droplets. The gas phase is described in the Eulerian frame while the discrete droplet phase is traced in the Lagrangian frame, with strong two-way coupling between the two phases through mass, momentum, and energy exchange. In the two-way coupling, distributing droplet source terms onto the Eulerian grids is a key procedure. Different distribution methods are compared to examine its impact on the statistics, including correlations between droplet source term and gas phase flow variables. The physical parameter considered is the characteristic droplet evaporation time, which is varied with the latent heat of vapourisation and plays a crucial role in both dynamic and evaporation effects of droplets on the turbulent reacting flow. To detail the analysis, the transport equation for the turbulence kinetic energy (TKE) is employed, in which the droplet contributions are categorised into three terms. The direct droplet and combustion effects on the TKE and their effects on the turbulence production and dissipation rate, pressure-dilatation are then scrutinised and compared to analyse the interactions among turbulence, combustion, and inert droplets in the multi-phase reacting flow.