Detached eddy simulation

Detached eddy simulation, usually shortened to DES, is a hybrid turbulence modelling approach used in computational fluid dynamics. It starts from a Reynolds-averaged Navier-Stokes (RANS) model and changes how that model behaves in parts of the flow field. Regions close to solid boundaries, and regions where the turbulent length scale is smaller than the largest grid dimension, are solved in the RANS mode. Where the turbulent length scale becomes larger than the local grid spacing, the model switches to a subgrid scale formulation of the kind used in large eddy simulation (LES), and the flow is solved in the LES mode. Because the fine, expensive resolution that pure LES needs is only demanded away from the walls, the grid requirements are lower and the cost of the computation falls considerably. DES was first formulated for the Spalart-Allmaras model, where it acts like LES with a wall model, but it can be built on other RANS models, such as two equation models, by changing the length scale the model uses, in which case it behaves as a hybrid RANS-LES model. It is a non-zonal approach that gives one smooth velocity field across the RANS and LES regions, although generating the grid is more complicated than for plain RANS or LES because of the switch between the two modes.