Dynamics of the transition region (grey area) in sensitized hybrid (U)RANS/LES modeling framework

Typically, a simple extension of RANS (Reynolds-Averaged Navier-Stokes) turbulence models, designed and calibrated in the steady framework, to an un- steady calculation (URANS) will result in a steady flow field, particularly for stable flows, i.e., attached and mildly separated flows. URANS methods fail to capture energetic and essential unsteady dynamics for globally unstable flows, even for massively separated flows. Therefore, an (instability) sensitized eddy- resolving model is designed based on the k-ζ-f model [1] and applied to attached and separated wall-bounded flow configurations – channel and periodic hill flows. Specifically, the model maintains the effects of vortex stretching, which appear to capture a departure from equilibrium more effectively. Particular focus has been placed on identifying the requirements for accurate description of grey re- gion dynamics between URANS and Large-eddy simulation mode. Additionally, the sensitivity of the resulting hybrid model regarding mesh resolution, mesh design, and the underlying RANS model has been investigated and compared to the IDDES methodology. The model demonstrates a robust and consistent be- havior when applied to different flow regimes at different mesh resolution/design and Reynolds numbers.

[1] DR Laurence, JC Uribe, and SV Utyuzhnikov. A robust formulation of the v2- f model. Flow, Turbulence and Combustion, 73(3):169–185, 2005.