Development of Alternative Shielding Functions for Detached-Eddy Simulations

This paper presents recent developments in finding alternative shielding functions in the framework of Delayed Detached-Eddy Simulation (DDES). The weaknesses of the standard shielding function are elaborated for the turbulent flow over a flat plate and an axisymmetric adverse pressure gradient flow. In both cases a small filter width compared to the boundary layer height caused a degeneration of the shielding function and led to severe model stress depletion. To overcome the strong grid dependency of the standard shielding two alternative shielding functions are proposed. The first determines the boundary layer edge by integrating the vorticity in the wall-normal direction, while separated flow is identified based on a comparative analysis of the individual vorticity components. For the second switching function the boundary layer edge is estimated by evaluating a localized formulation of the Bernoulli equation. The shielding disintegrates under resolved turbulent content by a sensor that includes the \(\sigma \)-velocity gradient operator. The novel shieldings are verified for basic canonical test cases. Compared to DDES, a superior protection of attached boundary layers could be demonstrated.