Recent progress on reliability assessment of large-eddy simulation

Reliability assessment of large-eddy simulation (LES) of turbulent flows requires consideration of errors due to shortcomings in the modeling of sub-filter scale dynamics and due to discretization of the governing filtered Navier–Stokes equations. The Integral Length-Scale Approximation (ILSA) model is a pioneering sub-filter parameterization that incorporates both these contributions to the total simulation error, and provides user control over the desired accuracy of a simulation. It combines an imposed target for the ‘sub-filter activity’ and a flow-specific length-scale definition to achieve LES predictions with pre-defined fidelity level. The performance of the ‘global’ and the ‘local’ formulations of ILSA, implemented as eddy-viscosity models, for turbulent channel flow and for separated turbulent flow over a backward-facing step are investigated here. We show excellent agreement with reference direct numerical simulations, with experimental data and with predictions based on other, well-established sub-filter models. The computational overhead is found to be close to that of a basic Smagorinsky sub-filter model.