Abstract

The feasibility of laminar flow control technology for future wing is bound to the development of a leading edge high-lift system that complies with the requirements on smooth surfaces to enable maintaining the laminar boundary layer flow, such as a Krueger flap. Although in principle the aerodynamic performance of a Krueger flap is known, the unsteady behaviour of the flow during deployment and retraction is completely unknown. This is as even more important as during deployment the Krueger flap is exposed to highly unfavourable positions perpendicular to the flow. To mitigate the risk of unfavourable aircraft behaviour, it is therefore expected that a Krueger flap has to be deflected significantly fast and may trigger unsteady aerodynamic effects. The European H2020 project UHURA, running from September 2018 to August 2022, has been focusing on the unsteady flow behaviour around such high-lift system and will first time deliver a deeper understanding of critical flow features at this type of high-lift device during their deployment and retraction together with a validated numerical procedure for its simulation. UHURA performed detailed experimental measurements in several wind tunnels to obtain a unique data set for validation purposes of Computational Fluid Dynamics (CFD) software, including detailed flow measurements by Particle Image Velocimetry (PIV) and other optical measurement technologies.

Abstract

The Chimera method [1] is an established method for simulation of overlapping grids. Meshing parts independently has made this method popular for complex geometries as well as moving bodies like propellers and rotors (e.g. [2]) or control surfaces (e.g. [3]). It is thus a promising method to simulate deflecting high-lift systems. 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 deg deflection) at a relatively high deflection speed (up to 200 deg/s) compared to classical leading edge devices. In terms of simulation, the grid properties of the overlapping mesh regions vary throughout the motion from a nearly sealed retracted position to a gapped flow in fully deflected position comparable to a slat device. This expects dynamic effects may get dominant and a valid simulation of this flow is needed for proper design and analysis. In the frame of the UHURA project1 , several partners applied their CFD capabilities based on Chimera in order to validate the method for this specific application in comparison to wind tunnel tests. The presentation outlines the different Chimera approaches ranging from structured/2D to hybrid/3D in steady and unsteady simulations for the different type of setups investigated, namely straight and swept wing with full-span and part-span Krueger flap. It summarizes common challenges and best practice for application of the Chimera approach for such a device.