Assessment of scaling laws for mixing fields in inter-droplet space

Droplet evaporation and subsequent mixing of the fuel vapor with the turbulent surrounding hot oxidizer has been simulated using direct numerical simulations (DNS). The kerosene droplets are fully resolved with realistic boundary conditions at the liquid-vapor interface to ensure the correct heat and mass transfer between the two phases. The study focuses on combustible mixture preparation in the inter-droplet space at scales larger than the quasi-laminar near droplet zone. The data are analysed with respect to key quantities for mixture fraction based combustion models such as mixture fraction distribution and its dissipation. The DNS is compared with scaling relationships for the wake and for length scales of Kolmogorov size where the wake seizes to be the dominant flow structure. The scaling relationships agree reasonably well with DNS data and they may serve as sub-grid scale closures for combustion models such as conditional moment closure or flamelets. Their respective regions of validity are quantified for the different cases of turbulence intensity that are investigated here.