FLUENT offers three different models for the detached eddy simulation: the Spalart-Allmaras model, the realizable
model, and the SST
In the DES approach, the unsteady RANS models are employed in the near-wall regions, while the filtered versions of the same models are used in the regions away from the near-wall. The LES region is normally associated with the core turbulent region where large turbulence scales play a dominant role. In this region, the DES models recover the respective subgrid models. In the near-wall region, the respective RANS models are recovered.
The application of DES, however, may still require significant CPU resources and therefore, as a general guideline, it is recommended that the conventional turbulence models employing the Reynolds-averaged approach be used for practical calculations.
The DES models, often referred to as the hybrid LES/RANS models combine RANS modeling with LES for applications such as high-Re external aerodynamics simulations. In FLUENT, the DES model is based on the one-equation Spalart-Allmaras model, the realizable - model, and the SST - model. The computational costs, when using the DES models, is less than LES computational costs, but greater than RANS.