Investigation of Subgrid-Scal Models in Large Eddy Simulation on the Unsteady Flow Around a Hydrofoil Using OpenFOAM

摘要

In this paper, we investigate the unsteady Reynolds-averaged Navier-Stokes simulations of the turbulent cavitating flow around a hydrofoil CLE. The primary objective of this study was to highlight the effect of subgrid-scale turbulence method in the prediction of unsteady vortical flow. In this work, the Smagorinsky and wall-adapting local eddy viscosity (WALE) models are selected to close the large eddy simulation equations. To investigate the limitations of these two models, the interactions between cavitation and vortices, the predicted streamlines, the velocities components, and the pressure oscillations have been discussed. The numerical results were compared with experimental results. These results showed that regardless of the selected turbulence model the development cycle of cavitation pocket is characterized by three levels: (first stage) the growth of attached pocket, (second stage) the separation of the attached pocket, and (last stage) the development and collapse of detached structures. The comparison between these two models shows that the WALE model takes into account both the rotation and strain rates, whereas the Smagorinsky model only takes into account the deformation rate of the turbulent structure. Besides, the WALE model is highly adaptive for wall-bounded flows. This advantage is explained by this ability to recover the near-wall scaling for the eddy viscosity. The WALE model has adopted a treatment without damping function or wall functions. Due to its algebraic nature, it offers a high-speed and efficient scheme compared to the Smagorinsky model. The study of the flow structures by iso-surface of the Q-criterion showed that the WALE model can predict the transition from laminar to the turbulent regime.