Reynolds Stress and PDF Modeling of Two-Way Coupling and Vaporisation Interaction in a Turbulent Spray Flame

Abstract

In turbulent spray flames the momentum and mass transfer between fuel droplets and gas phase influence the turbulence properties of the gas phase. The importance of these two-way coupling effects are investigated numerically by means of a transported Probability Density Function (PDF) method and compared with experimental data of a turbulent non-premixed methanol spray flame obtained by Karpetis and Gomez. We focus on the development of a Reynolds stress model that takes into account the presence of particles and vaporisation. A hybrid Finite Volume/ Monte Carlo method is used to solve the gas phase properties and a Lagrangian particle method is used to solve the dispersed phase properties. The model for the pressure-rate-of-strain is extended to take into account interaction effects and an exact model for the effect of vaporisation on the turbulence dissipation is proposed. The drag reduction and the heat and mass transfer coefficient of the fuel droplets due to vaporisation is taken into account based on numerical correlations found by Chiang, Raju and Sirignano. Comparison between simulations and experimental data show that two-way coupling and vaporisation prevent the droplets from completely relaxing to the gas phase conditions. The two-way coupling terms appearing in the model for the pressure-rate-of-strain are of the same order of magnitude as the classical two-way coupling terms and can therefore not be neglected.