Investigation of Airfoil Self-Noise Generation and Propagation Using Large Eddy Simulation, Analytical Models and Acoustic Analogy

Abstract

The present work concerns the investigation of airfoil noise generated by the unsteady flow past an airfoil and its subsequent propagation to the far-field. This study is of paramount importance for the design of aerodynamic configurations such as wings and high-lift devices, as well as wind turbine blades, fans and propellers. In this project, we will primarily investigate 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 instability waves along laminar boundary layers. The turbulent aerodynamic flows analyzed give rise to noise sources at a broad range of frequencies and spatial scales. Therefore, large eddy simulation (LES) is the numerical method of choice for the flow simulations since it captures the most energetic scales associated with noise generation at an affordable computational cost compared to direct numerical simulation (DNS). The acoustic predictions will be performed by the Ffowcs Williams-Hawkings (FWH) acoustic analogy formulation and by Amiet's trailing edge noise theory. The surface and volume integrations of dipole and quadrupole source terms appearing in the FWH equation will use a 3-D wideband multi-level adaptive fast multipole method (FMM) in order to accelerate the calculations. Such numerical tool allows the analysis of the noise radiation associated with surface and volume sources separately. Therefore, it is possible to investigate the effects of dipole and quadrupole sources for each configuration, as well as the effects of convection on the computation of noise radiated by these sources. Numerical simulations will be conducted for a NACA0012 airfoil for four flow configurations with different angles of incidence, freestream Mach numbers and boundary layer tripping combinations. For all configurations, the flow Reynolds number based on the airfoil chord will be fixed at Re=408,000. Flow simulation results and aeroacoustic predictions will be compared to experimental data available in the literature.