CAA-Simulation of Flap Noise Generation using Perturbation Equations

The interaction of vorticity with high lift systems of airfoils is an important source of airframe noise. In the framework of the SWING project, noise generation measurements at a wing section of a modern transport aircraft with deployed flap have been performed, where the influence of a flap cove cover on the radiated sound was examined. In the present paper, these experiments will be studied numerically using the DLR CAA-code PIANO. In PIANO, the interaction of a single vortex with a flap is calculated by the solution of nonlinear perturbation equations with a RANS mean flow. Non-linearities are taken into account up to first order. Self excited oscillations of the disturbance quantities, which are a consequence of the unstable mean flow field are tried to suppress by introduction of a wall damping term in the momentum equations which shall enforce a no slip boundary condition also for the disturbance flow field. It will be shown that the success of this procedure depends on the details of the mean flow field. Qualitative agreement with the experimental results has been found