Numerical simulation of two-phase flow: Air-mist film cooling over a flat plate

The performance of air-mist film cooling is evaluated for varying mist concentrations (2-7%) and droplet diameters (5-30 mu m) using the Euler-Lagrange approach with the k - epsilon realizable model with enhanced wall treatment. The jet-crossflow interactions induce complex droplet dynamics, illustrating a highly skewed jet at the hole exit with the concentration of droplets and momentum on the windward side, while the counter-rotating vortex pair (CRVP) appears on the leeward side. The downstream evolutions of droplets, their evaporation, and the thermal field are considerably influenced by the mist concentration and droplet diameter. The introduction of droplets in the secondary flow brings in significant improvements in film cooling effectiveness both in streamwise and spanwise directions. Although the spanwise non-uniformity of the thermal field is high, droplets of 10 mu m at a mist concentration of 5% provide the optimal protection of the surface, where the trajectory of the secondary jet and that of droplets are in concurrence for the freestream conditions. The droplet dynamics exhibit the two-layer system for a relatively larger diameter, where droplets penetrate more into the crossflow and stay away from the surface.