Research on LES for Flows with Generation of Turbulence at Small Scales

present study was to identify The structure which is most responsible for Thetransfer and dissipation of the turbulent energyand conduct an assessment of the subgrid scale (SGS) models in large-eddy simulation (LES) on theaccuracy for a prediction of energy transfer associated with these structures.We have developed amethod to classify vortical structures into three categories, a flat sheeta cylindrical sheet and a tube core. We generated direct numerical simulation (DNS) data of thehomogeneous isotropic turbulence using 128 wid13 D1 and 256 wid13 D1 grid points for the cases withwithout inputs of external energy at the large or small scales.这是应该使用这些databases that the proposed method yields an accurate classification of the data into three regionswith the desired characteristics. By utilizing this method我们examined the contribution of these structures for the dissipation and cascade of turbulent energyin LES. It shown that dissipati…More on and forward energy transfer primarily arises in the flat sheet regionwhereas backward transfer primarily occurs in the compressed tube核心领域。in all of threeregions, an intense generation of the azimuthal vorticityplaced perpendicular to the most stretched vorticity, was noticed.Then，我们已经承诺了SGS models对结构结构的评估responsible for the transfer. the constant coefficient Smagorinsky model was an accurate model torepresent the forward transfer. In the dynamic Smagorinsky model （DSM）the effect of the strain on the model was reduced，and an prediction accuracy for the structures responsible for energy transfer was significantlylowered.These SGS models further assessed in actual LES. The Smagorinsky model yieldedoverestimate of forward transfer，and a poor prediction for an evolution of vortical structures. DSM yielded overestimate ofcontribution of the tube-core regionand a poor prediction of the dissipative structures. These drawbacks were circumvented in the SGSestimation model. Assessment of the results obtained in the present研究at higher Reynolds numberswill be left to future work. Less

The aim of the present study was to identify the structure which is most responsible for the transfer and dissipation of the turbulent energy, and conduct an assessment of the subgrid scale (SGS) models in large-eddy simulation (LES) on the accuracy for a prediction of energy transfer associated with these structures.We have developed a method to classify vortical structures into three categories, a flat sheet, a cylindrical sheet and a tube core. We generated direct numerical simulation (DNS) data of the homogeneous isotropic turbulence using 128ィイD13ィエD1 and 256ィイD13ィエD1 grid points for the cases with and without inputs of external energy at the large or small scales. It was shown using these databases that the proposed method yields an accurate classification of the data into three regions with the desired characteristics. By utilizing this method, we examined the contribution of these structures for the dissipation and cascade of turbulent energy in LES. It was shown that dissipati … More on and forward energy transfer primarily arises in the flat sheet region, whereas backward transfer primarily occurs in the compressed tube core region. In all of three regions, an intense generation of the azimuthal vorticity, placed perpendicular to the most stretched vorticity, was noticed.Then, we have conducted an assessment of the SGS models on its accuracy for prediction of the structures responsible for the transfer. The constant coefficient Smagorinsky model was an accurate model to represent the forward transfer. In the dynamic Smagorinsky model (DSM), the effect of the strain on the model was reduced, and an prediction accuracy for the structures responsible for energy transfer was significantly lowered.These SGS models were further assessed in actual LES. The Smagorinsky model yielded overestimate of forward transfer, and a poor prediction for an evolution of vortical structures. DSM yielded overestimate of contribution of the tube-core region, and a poor prediction of the dissipative structures. These drawbacks were circumvented in the SGS estimation model. Assessment of the results obtained in the present study at higher Reynolds numbers will be left to future work. Less