Effects of heat release on turbulence characteristics in a three-dimensional spatially developing supersonic droplet-laden mixing layer

Abstract

By direct numerical simulations, the effects of heat release on turbulence characteristics are systematically investigated in a three-dimensional spatially developing supersonic droplet-laden mixing layer with the convective Mach number of 1.2. A one-step Arrhenius global reaction mechanism is employed for the combustion of n-decane and the liquid fuel is supposed to be fully atomized point droplets. The reactive and inert simulations are both conducted for comparison. The thermal-runaway ignition occurs in the transition region and the flame surfaces distribute at the upper and lower edges of the mixing layer. The diffusion combustion happens on the hot side, but the flame tends to extend towards the cold fuel layer with more vigorous chemical reactions, where the premixed combustion mode dominates. The combustion heat release makes the droplets gradually spread downwards and the tendency that the droplets accumulate in the low-temperature and high-density regions is augmented. Under the effects of chemical reactions, the mixing layer asymmetry is enhanced with the shear layer center further skewing towards the hot side and turbulence anisotropy is augmented due to the reduction of the pressure-strain rate. The fluctuations of temperature, density and species mass fractions are also augmented and two peaks appear at the positions of flame surfaces on the hot and cold sides, where the lower peak is more significant. However, the Reynolds stresses are attenuated, but exhibit the inflection points with larger magnitude on the cold side, which is attributed to the viscous transport and the enhancement of thermodynamic fluctuations.