A Simple DDES Shielding Technique to Mitigate Modeled-Stress Depletion and Promote Rapid RANS-to-LES Transition

This work presents a straightforward modification to the standard DDES shielding function that mitigates both modeled-stress depletion and delayed LES transition—two persistent challenges for hybrid RANS-LES methods. The approach centers on a new suppression function that weakens or deactivates RANS shielding when separated or detached flow is detected, based solely on the local flow orientation and the gradient of wall-normal distance. The formulation is entirely local, relying only on quantities within the solution stencil that are already available in the underlying RANS model, and it can be readily implemented into existing DDES codes. Although presented here in the context of SA-based DDES, the technique is general and amenable to alternate RANS closures. The new method is implemented in both FUN3D’s finite-volume and stabilized finite-element solvers. It is first evaluated on a simple attached flow over a NACA 0012 airfoil and then on several NASA High-Lift Common Research Model (CRM-HL) configurations from the Fifth High-Lift Prediction Workshop (HLPW-5). The modification is shown to effectively mitigate modeled-stress depletion with increasing grid refinement and is compared with wall-modeled LES and wind-tunnel experiments on the CRM-HL in full landing configuration.