Trailing-Edge Noise Predictions Using Compressible Large-Eddy Simulation and Acoustic Analogy

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The present investigation of airfoil trailing-edge noise generation and propagation concerns the broadband noise that arises from the interaction of turbulent boundary layers with the airfoil trailing edge and the tonal noise that arises from vortex shedding generated by laminar boundary layers. Large-eddy simulations are conducted for a NACA0012 airfoil with rounded trailing edge for two flow configurations with different freestream Mach numbers (M1 � 0:115 and 0.4) for an angle of incidence of 5 deg. The Reynolds number based on the airfoil chord is fixed at Rec � 408;000. The acoustic predictions are performed by the Ffowcs Williams and Hawkings acoustic analogy formulation and incorporate convective effects. Surface and volume integrations of dipole and quadrupole source termsappearingintheFfowcsWilliamsandHawkingsequationareperformedusingathree-dimensionalwideband multileveladaptivefastmultipolemethodtoacceleratethecalculationsofaeroacousticintegrals.TheeffectsofMach numberandnonlinearquadrupolesources areassessed.Nonlinear quadrupolenoise sourcesplay animportant role infar-fieldsoundradiationforthehigherMachnumber flowconfiguration,M1 � 0:4.Ascalingstudyisperformed and, although surface pressure spectra scale with hydrodynamic scaling, far-field acoustics has a more complex behavior. The broad vortex-shedding tone generated by the laminar boundary layer vortex shedding noise causes a departure from the classical fifth power-law scaling, a behavior also seen in previous experiments.