Large Eddy Simulation (LES) has had very limited impact on industrial CFD simulations, mainly due to its high computational costs. There are only very few technical applications, where LES can be applied within the entire computational domain. Such flows are typically of very low Reynolds number, or flows where wall boundary layers are not important (free shear flows). Especially the high resolution requirements for wall bounded flows even at moderate Reynolds numbers have severely limited the usage of LES.

In order to allow the resolution of large turbulent structures in industrial flow simulations, hybrid models like Scale-Adaptive Simulation (SAS) (see Scale-Adaptive Simulation (SAS) Model), Detached Eddy Simulation (DES) (see Detached Eddy Simulation (DES)), Shielded Detached Eddy Simulation (SDES) (Shielded Detached Eddy Simulation (SDES)), and Stress-Blended Eddy Simulation (SBES) (Stress-Blended Eddy Simulation (SBES)) have been developed. For these models, the wall boundary layers are typically covered by the RANS part of the model and turbulence is only resolved in large separated (detached) zones. The unsteadiness in the simulations is generated from a global flow instability as observed behind bluff bodies. However, such an approach is not always suitable, as not all flows exhibit a sufficiently strong instability to generate turbulent structures by themselves. In such situations, zonal models are desirable, where a clear distinction between RANS and LES regions can be made and where turbulence is converted from RANS to LES by suitable methods at the interface. One such approach is ELES, where you generate RANS and LES zones during the grid generation phase, select appropriate models for each zone, and define the appropriate treatment at the interface. ELES is therefore not a new turbulence model, but the combination of RANS and LES models joined by appropriate interface conditions.