Aerodynamics and aeroacoustics study of the flow around an automotive fan airfoil

Turbulent flows around airfoils are very challenging to simulate accurately because of the complex flow phenomena, including leading-edge boundary layer separation, shear layer transition to turbulent behavior, reattachment and trailing-edge vortex shedding. In this paper, the flow around a CD (Controlled-Diffusion) airfoil is studied at a Reynolds number of 160,000 using Large-Eddy Simulations (LES). The in-house hybrid spectral/finite element SFELES solver [1] is used to solve the flow. The aim of this research is to study the unsteady turbulent boundary layer and to predict the corresponding wall-pressure spectrum which will be used for the noise predictions, to implement and evaluate the new SGS model proposed recently by G. Ghorbaniasl et al. [2] and to study the influence of the LES sub grid-scale models on the results. Another goal is to calculate the radiated broadband trailing-edge noise by applying Amiet's aeroacoustic theory and its extensions [3, 41 using the wall-pressure spectrum for a station near the trailing edge. The sound pressure level and its directivity are computed for the three SGS models. The aerodynamics and aeroacoustics results are compared with experimental results obtained by Moreau and Roger [5] and Moreau et al. [6] as well as other numerical results obtained by Christophe [7] using OpenFoam and Wang et al. [8] using a hybrid finite differences/spectral solver. The high variability of the leading edge recirculation bubble size with the SGS model is found. The predicted noise spectra is found insensitive to the choice of the SGS model, the difference does not exceed 2 dB for frequencies of interest (100-2000 Hz). This is linked to the insensitivity of the wall-pressure spectra to the choice of the SGS model.