Large-Eddy Simulation of Transition to Turbulence using the Two-Level Simulation Approach

In the present study, the two-level simulation (TLS) model,1 a multi-scale modeling strategy, is assessed for its capabilities for large-eddy simulation (LES) of transition to turbulence in the Taylor-Green vortex (TGV) flow. The TLS model was originally developed for high Reynolds number (Re) fully developed turbulent flows, and later was extended in form of the hybrid TLS-LES strategy for efficient computation of such flows by additively blending the TLS model with a conventional LES strategy. Compared to the conventional algebraic and transport equation based subgrid-scale closures (SGS) for LES, where the effects of the unresolved small-scales (SS) of motion on the resolved large-scales (LS) of motion are modeled, in the TLS model, both large- and small-scales are explicitly evolved in a coupled manner. In this study, the capabilities of the TLS model for capturing the features of flow during the laminar to turbulent transition is assessed by considering the Taylor-Green vortex (TGV) flow at Re = 800, which exhibits transition and subsequent turbulence decay. The assessment of the TLS model in an a priori manner shows that the two-scale decomposition strategy and the modeling assumptions are adequate for this particular flow. The a posteriori assessment of the TLS model and a comparison with the conventional LES strategy shows its improved performance in capturing aspects of transition in the TGV flow.