Sub-grid Scale Modeling in Large Eddy Simulation with Variable Eddy-Viscosity Coefficient

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Javad Taghinia Name of the doctoral dissertation Sub-grid Scale Modeling in Large Eddy Simulation with Variable Eddy Viscosity Coefficient Publisher School of Engineering Unit Department of Applied Mechanics Series Aalto University publication series DOCTORAL DISSERTATIONS 195/2015 Field of research Fluid Dynamics Manuscript submitted 21 April 2015 Date of the defence 26 November 2015 Permission to publish granted (date) 27 October 2015 Language English Monograph Article dissertation (summary + original articles) Abstract Two new sub-grid scale models for large eddy simulation (LES) are presented; namely zero and one-equation SGS models. These models utilize a novel method for calculating Cu in which the model coefficient is determined from the strain-rate and vorticity parameters. Therefore, it responds to both the shear and vorticity dominated flows that are far from equilibrium. The Cu usually ensures realizability of the resolved normal stresses in question. Unlike the dynamic Smagorinsky model (DSM), both models need only a single filter making them more robust for use in the majority of fluid flow problems. In addition, they require no ad-hoc strategies for achieving the numerical stabilization. Finally, one can save some computational effort in the proposed models, since the test-filtering operation on the SGS stress is not required. In other words, the current models can be considered as a good compromise between accuracy and manageability; particularly, as simple as the original Smagorinsky model and as accurate as the DSM. The performance of the new models are demonstrated through the comparison with experimental and DNS data of well-documented flows, consisting of fully developed channel flows, indoor airflow, flow over circular cylinder and jet impingement on a concave surface. The predictions are in good agreement with the available data. The test cases are selected such as to justify the ability of the model to replicate the combined effects of low-Reynolds number (LRN), near-wall turbulence and nonequilibrium. Comparisons also indicate that the present model offers competitiveness with the existing SGS models.Two new sub-grid scale models for large eddy simulation (LES) are presented; namely zero and one-equation SGS models. These models utilize a novel method for calculating Cu in which the model coefficient is determined from the strain-rate and vorticity parameters. Therefore, it responds to both the shear and vorticity dominated flows that are far from equilibrium. The Cu usually ensures realizability of the resolved normal stresses in question. Unlike the dynamic Smagorinsky model (DSM), both models need only a single filter making them more robust for use in the majority of fluid flow problems. In addition, they require no ad-hoc strategies for achieving the numerical stabilization. Finally, one can save some computational effort in the proposed models, since the test-filtering operation on the SGS stress is not required. In other words, the current models can be considered as a good compromise between accuracy and manageability; particularly, as simple as the original Smagorinsky model and as accurate as the DSM. The performance of the new models are demonstrated through the comparison with experimental and DNS data of well-documented flows, consisting of fully developed channel flows, indoor airflow, flow over circular cylinder and jet impingement on a concave surface. The predictions are in good agreement with the available data. The test cases are selected such as to justify the ability of the model to replicate the combined effects of low-Reynolds number (LRN), near-wall turbulence and nonequilibrium. Comparisons also indicate that the present model offers competitiveness with the existing SGS models.