Abstract
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.
Highlights
Turbulent two-phase flows are ubiquitous in many mechanical, chemical, and metallurgical systems such as liquid atomizers, bubble column reactors, emulsions, and continuous casting
By implementing the corrected eddy viscosity term into the three functional closure models for the subgrid stresses, surface tension force, and the residual term in continuity equation, a complete two-phase large eddy simulation (LES) platform is established which is used for the coarse-grid simulation of two turbulent interfacial flow benchmarks
An a-posteriori analysis of a fully-functional, Favre-filtered LES-volume of fluid method (VOF) approach is presented in which all the subgrid scale (SGS) terms are modeled based on a revisited eddy viscosity assumption for the two-phase LES
Summary
Turbulent two-phase flows are ubiquitous in many mechanical, chemical, and metallurgical systems such as liquid atomizers, bubble column reactors, emulsions, and continuous casting. They tested the validity of this conclusion by an a-posteriori simulation of the liquid jet atomization problem (Ketterl et al, 2019) In another a-priori study, Vincent et al (2018) conducted a comprehensive analysis of the different structural and function SGS models using the turbulent phase inversion (PI) problem and reported that the approximate deconvolution method (ADM) (Stolz and Adams, 1999) reveals the highest correlations with fine-grid data for all the unresolved terms. By implementing the corrected eddy viscosity term into the three functional closure models for the subgrid stresses, surface tension force, and the residual term in continuity equation, a complete two-phase LES platform is established which is used for the coarse-grid simulation of two turbulent interfacial flow benchmarks.
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