9. Lessons Learnt from Chimera Method Application to a Deploying Krueger Device

The motion of the Krueger flap—as the most promising leading edge high-lift system device for laminar wing technology—is characterized by a relatively large movement (about 140° deflection) at a relatively high deflection speed (up to 200°/s) compared to classical leading-edge devices. The configuration varies throughout the motion from a nearly sealed retracted position to a gapped flow in fully deflected position, comparable to a slat device. During its deployment or retraction phase, highly unsteady flow is observed, leading to both performance degradation and loads fluctuations on the different elements (Krueger panels for instance). For proper design and analysis, a validated numerical simulation tool considering both the change in external shape and the unsteady flow feature is necessary. The evaluation of such numerical tools and their validation based on dedicated experiments is the core of the UHURA EU funded project. In terms of numerical simulation, the Chimera method is an established method for simulation of moving bodies by employing overlapping grids. In the framework of the UHURA project, several partners applied their CFD capabilities, mainly URANS, based on the Chimera technique in order to validate the method for this specific application in comparison to wind tunnel tests. This paper outlines the different Chimera approaches ranging from structured/2D to hybrid/3D in steady and unsteady simulations for the different types of setups investigated, namely straight and swept wing with full-span and part-span Krueger flap. It summarizes common challenges and best practices for the application of the Chimera approach for such a device.