The Simulation of Airframe Noise Applying Euler-Perturbation and Acoustic Analogy Approaches

Kurzfassung

The application of perturbation approaches to simulate airframe noise mechanisms of aircraft during landing approach is discussed. Euler-perturbation approaches that simulate sound generation at obstacles due to upstream injected test-vorticity allow to assess the efficiency of a geometry to transform vortical energy into acoustic energy. Acoustic analogies with sources determined either by an unsteady flow simulation or described statistically yield hybrid two-step methods that in addition take into account the turbulent source strength. An acoustic analogy is presented that uses acoustic perturbation equations (APE)for the simulation of the acoustic radiation problem in space and time. The acoustic convection and refraction effects are part of the simulation of wave propagation such that the source domain is limited to the vicinity of the sound generating geometry where the unsteady vorticity has a considerable magnitude. Using linearized acoustic perturbation equations the unbounded growth of hydrodynamic instabilities in critical mean flows is prevented completely. Computational results for trailing edge noise based on a Large Eddy Simulation (LES) of the compressible flow problem and acoustic perturbation equations for the acoustic simulation are presented. The acoustic source terms are computed furthermore from a synthetic turbulence model and first results for trailing edge noise are presented. The far field sound field is computed via Kirchhoff extrapolation.