Favre-filtered LES-VOF of two-phase flows with eddy viscosity-based subgrid closure models: An a-posteriori analysis

Developing functional closure models for all the subgrid scale (SGS) physics in the large eddy simulation (LES) of turbulent two-phase flows is yet a challenging task due to the complicated turbulence-interface interactions. Our recent study (Saeedipour and Schneiderbauer, 2019) has revisited the classical eddy viscosity concept for the two-phase flows and proposed a new approach to include surface tension into the subgrid eddy viscosity. It has revealed an a-priori competence for the accurate simulation of the interfacial turbulence using the volume of fluid (VOF) method. The present study aims to exploit the potentials of this approach in an a-posteriori manner, which could be an important step towards the fully-functional LES models for two-phase flows. On the basis of the Favre-filtered governing equations, the corrected eddy viscosity model is adopted to close the convective, surface tension, and continuity SGS terms and establishes a functional LES-VOF approach. The models are implemented into an OpenFOAM-based geometric VOF solver. To perform the a-posteriori analysis two benchmark problems are considered: (i) a 2D turbulent phase inversion as also used for a-priori analysis, and (ii) a 3D freely-decaying, homogeneous isotropic turbulent flow in the presence of an initially flat interface. The results reveal that compared to the conventional Smagorinsky model, the proposed LES-VOF method reveals a better performance in predicting the local turbulence characteristics as well as the energy spectra, particularly at flows with density contrasts. Also, the size distribution of the droplets shows a better agreement with the fully-resolved data. The a-posteriori analysis further unveils the importance of subgrid surface tension and the SGS residual term in the continuity equation in the development of the interfacial characteristics. The original contribution of this study lies in proposing a full LES approach for the two-phase flows with functional SGS models based on the revisited eddy viscosity concept. This method can be used for more accurate coarse-grid simulation of industrial problems with dispersed droplet regimes.

Automated summary

Developing functional closure models for subgrid scale (SGS) physics in large eddy simulation (LES) of turbulent two-phase flows is challenging due to complicated turbulence-interface interactions. A new approach incorporating surface tension into subgrid eddy viscosity has shown promise for accurate simulation of interfacial turbulence. Implementing this approach in an a-posteriori manner has demonstrated improved performance in predicting local turbulence characteristics and energy spectra, particularly in flows with density contrasts.