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The interaction of the turbulent wakes of the rotor with the outer guide vanes is one of the main broadband noise source in turbofan engines at approach conditions. Hence its prediction and reduction is a priority for engine manufacturers. The development of numerical methods is required as analytical approaches are limited to simple geometries and simplified flow configurations. The linearized Euler equations are solved in the time-domain to model the response of an isolated airfoil interacting with turbulence that is stochastically synthesized and injected in the computational domain through vorticity sources. This new method of injection has the advantages of being easy to implement and parallelize in an existing solver, whilst the generated turbulence is frozen. The method is firstly validated on a 2D free-field configuration. It is then applied, in the framework of the Fan Stage Broadband Noise Benchmarking Programme, to a two-dimensional NACA 65(12)-10 airfoil with no angle of attack and the results are validated through comparisons with experimental data. Afterwards, the effect of the angle of attack is studied and the results suggest that a one-component turbulent model is not satisfactory to perform accurate acoustic predictions with an angle of attack, as it overestimates the rate of decay of the acoustic spectra at high frequencies. The study of the influence of the integral length scale of the turbulence confirms that the airfoil leading edge response is only modulated by the incoming turbulence characteristics. Finally, the acoustic spectra predicted for different velocities show a better agreement with a flat plate analytical model when the velocity is increased.

CAA Study of Airfoil Broadband Interaction Noise Using Stochastic Turbulent Vorticity Sources<br />