Trailing Edge Noise Predictions Using Compressible LES and Acoustic Analogy

Abstract

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 (LES) are conducted for a NACA0012 airfoil with blunt rounded trailing edge for three flow configurations with different freestream Mach numbers (M∞ = 0.115 and 0.4) and angles of incidence (AoA = 0 and 5 deg.). The Reynolds number based on the airfoil chord is fixed at Rec = 408000. The acoustic predictions are performed by the Ffowcs Williams & Hawkings (FWH) acoustic analogy formulation and incorporate convective effects. Surface and volume integrations of dipole and quadrupole source terms appearing in the FWH equation are performed using a 3D wideband multi-level adaptive fast multipole method (FMM) in order to accelerate the calculations of aeroacoustic integrals. The effects of Mach number and non-linear quadrupole sources are assessed. In order to validate the numerical solutions, flow simulation and acoustic prediction results are compared to experimental data available in the literature and excellent agreement is observed. Non-linear quadrupole noise sources play an important role in farfield sound radiation for the higher Mach number flow configuration, M∞ = 0.4, for both the tonal peak frequency and higher frequencies. A scaling study is performed and, although surface pressure spectra scale with hydrodynamic scaling, farfield 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.