Large-Eddy Simulation

Large eddy simulation (LES) is a solution technique for the large, energetic eddies of a turbulent flow, in which the dissipative behavior of the small eddies is modelled. Consider the energy spectrum presented in the figure below.

The transfer of energy occurs from large to small eddies (energy cascade), where viscous dissipation takes place. In DNS, every frequency mode is resolved by the solution of the Navier-Stokes equation with appropriate resolution. In LES, the large eddies (low frequency) are resolved, while the small (high frequency) are not. Instead, they’re modelled by a subgrid stress. Ideally, the LES cut-off must be in the lower end of the inertial subrange.

Note

The inertial subrange is the scale range to which only energy transfer from large to small eddies (cascade) occurs. Hence it does not include the small scales in which viscous dissipation takes place.