Unsteady Simulation of The Flow During the Deployment of High-Lift Systems

Kurzfassung

This study focuses on the numerical simulation of the unsteady two-dimensional flow during the deployment and retraction of the slats and flaps of a transport aircraft wing section, using the compressible unsteady RANS solver DLR Tau with the Chimera technique. The unsteady simulations reveal a sudden growth of the flow separation on the flap after the end of the movement of the devices. Except when this happens, the unsteady lift coefficient of the flap moving alone can be predicted by quasi-steady corrections. The motion of the slat has a much more complicated impact on the flow. Generally speaking, the time-delays are high. If confirmed, these effects may have a significant impact on flight dynamics. A Fourier analysis reveals a low-frequency oscillation which may be an eigenmode of the flap. It also reveals how the vortex shedding predicted at the trailing edge of the flap develops when the slat and the flap have stopped moving. This may be a relevant acoustic source. The Chimera method enables a great flexibility, but it introduces significant numerical dis-turbances for both steady and unsteady solutions. This study shows that they are mainly caused by interpolations performed from a fine mesh to a mesh having a lower resolution. An integral formulation is suggested to improve the non-conservative behavior of the method. The reliability of these results still has to be assessed thanks to other numerical simulations, as wind-tunnel or in-flight tests seem unfeasible.