A comparative study of two-phase coupling models for a sparse-Lagrangian particle method

Simulations of spray combustion in statistically homogeneous turbulence with different droplet loadings are performed using a sparse-Lagrangian particle method called MMC. We compare different models for the distribution of the droplet source terms to the notional particles with corresponding CP-DNS data and solutions of a dense particle method that employs standard models for the two-phase coupling. Good agreement of unconditional mean and rms of the reactive scalars is found for both, the sparse particle method utilizing a one-to-one coupling technique between the droplets and the stochastic particles, and the dense particle method where the droplet mass is distributed equally to all particles within the computational cell. MMC predictions of the mixture fraction variance are somewhat superior to predictions by the dense particle method, but conditional fluctuations are underpredicted in both models. In contrast, MMC gives accurate predictions of the conditional mean temperature and its conditional variance if the droplet mass is preferentially distributed to particles closest to saturation conditions. The unconditional variance is, however, significantly overpredicted due to a pronounced peak at saturation conditions in the composition PDF. Attempts to incorporate the latter approach into the one-to-one coupling strategy are presented and allow for some control of gas-phase variance generation due to droplet evaporation. However, improvements have only been achieved for transitional periods but not for the entire duration of the spray combustion process, and - in the absence of suitable blending functions between the different approaches - the one-to-one coupling strategy currently seems the most appropriate choice for two-phase coupling in MMC.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

In this study, simulations of spray combustion in statistically homogeneous turbulence were carried out using the MMC method. The results were compared with experimental data and a dense particle method, and good agreement was observed in terms of mean and rms of reactive scalars. Although MMC predictions of mixture fraction variance were superior, both MMC and the dense particle method underpredicted conditional fluctuations. Accurate predictions of conditional mean temperature and its variance were achieved with MMC when the droplet mass was preferentially distributed to particles closest to saturation conditions. Attempts to incorporate this approach into the one-to-one coupling strategy showed some improvement but only for transitional periods. Overall, the one-to-one coupling strategy currently seems to be the most appropriate choice for two-phase coupling in MMC.