4.10 Detached Eddy Simulation (DES)

This section describes the theory behind the Detached Eddy Simulation (DES) model. For details about using the model in ANSYS FLUENT, see this chapter and this section in the separate User's Guide.

Overview

ANSYS FLUENT offers three different models for the detached eddy simulation: the Spalart-Allmaras model, the realizable $k$- $\epsilon$ model, and the SST $k$- $\omega$ model.

In the DES approach, the unsteady RANS models are employed in the boundary layer, while the LES treatment is applied to the separated regions. The LES region is normally associated with the core turbulent region where large unsteady turbulence scales play a dominant role. In this region, the DES models recover LES-like subgrid models. In the near-wall region, the respective RANS models are recovered.

DES models have been specifically designed to address high Reynolds number wall bounded flows, where the cost of a near-wall resolving Large Eddy Simulation would be prohibitive. The difference with the LES model is that it relies only on the required resolution in the boundary layers. 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 ANSYS FLUENT, the DES model is based on the one-equation Spalart-Allmaras model, the realizable $k$- $\epsilon$ model, and the SST $k$- $\omega$ model. The computational costs, when using the DES models, is less than LES computational costs, but greater than RANS.