Hybrid Overset-LES Simulations of Noise Reduction Concepts of Loaded Airfoils

The noise reduction potential of a loaded airfoil is investigated by means of a novel Overset-LES simulation method. This aerodynamic noise prediction tool solves the compressible Navier-Stokes equations, supplemented with a sub-filter-stress model, in perturbation form over a background flow. The such obtained noise sources are subsequently propagated with wave propagation equations to the far-field (e.g., with the Acoustic Perturbation Equations). This hybrid prediction method is applied to a noise reduction investigation of a loaded airfoil. For this purpose, two geometries are considered, i.e., a reference geometry and a modified geometry with a long-chord slat. The effect of the long-chord slat on the turbulent sound sources is investigated by mainly considering turbulence statistics in the slat cove and shear-layer reattachment location. Moreover, the acoustic far-field propagation revealed the influence of a long-chord slat on the directivity. The slat noise reduction primarily results from the combined effect of the less intense shear-layer instabilities and the larger distance between reattachment location and upper trailing-edge, rather than a shielding effect by the long-chord slat. The predicted noise reduction matches well with values reported in literature.