Large eddy simulation of a transitional flow over an airfoil
Turbulence is made of eddies that appear over a wide range of scales, large eddies are anisotropic, whilst small eddies are isotropic. In order to avoid direct numerical simulation (DNS), some level of modeling should be introduced to reduce computational cost.
The large eddy simulation is a computational method that allows the removal of eddies at the smallest scales using a low-pass filter which is applied to the Navier-Stokes equation.
All the equations in an LES computational method are time dependent, the length attribute to the filter used in the method is called the cutoff length which is related to the mesh spacing. Scales of motions that are larger than the cutoff length are resolved in the simulation and those that are smaller than the cutoff length are modeled.
For Large Eddy Simulations to produce reasonable flow predictions, the modeled scales of motions should be isotropic and in average 80% of the energy cascade must be resolved.
Smagorisnky Subgrid Model
Finite values of eddy viscosity is predicted by the model in laminar areas where there is shear.