  A novel variant of Improved Delayed Detached-Eddy Simulation based on a
differential Reynolds-stress background model is presented. The approach aims
to combine the advantages of anisotropy-resolving Reynolds-stress closures in
the modelled RANS regions with consistent LES and wall-modelled LES behaviour
in the resolved flow regions. In computations of decaying isotropic turbulence
with a low-dissipative flow solver it is shown that a straightforward
hybridised Reynolds-stress model provides insufficient turbulent dissipation as
sub-grid closure in the LES regions and is therefore locally replaced by scalar
viscosity modelling. Simulations of periodic channel flows at different
Reynolds numbers and grid resolutions are used to calibrate and validate the
wall-modelled LES branch of the new model. A final application in embedded
wall-modelled LES of a flat-plate boundary layer is widely consistent with
results using the SST-RANS background model, but shows some deviations from the
Coles-Fernholz skin-friction correlation. In this regard, initial sensitivity
studies indicate possible adverse effects due to the synthetic-turbulence
approach used in these simulations.
