Numerical simulation of turbulence interaction noise applied to a serrated airfoil

Abstract

Turbulent wakes generated by turbofan blades and interacting with the outlet guide vanes are known to be
mainly contributing to broadband noise emission of aero-engines at approach conditions. Analytical approaches,
such as the well-known Amiet's model can be adopted to estimate the noise generated by turbulent flows
impacting thin airfoils, but they are limited by the flat-plate assumptions. The development of numerical
methods allowing more complex geometries and realistic flows is required. The method, described in the present
paper, is based on a CAA code solving the nonlinear Euler equations. The upstream turbulence is synthesized
from a stochastic model and injected into the computational domain through an adapted boundary condition. It is
first validated in 2D and 3D against academic flat plate configurations by comparison with Amiet solutions
(exact in such cases). Then, 3D computations are applied to simulate the effect of a passive treatment (leading
edge serrations) aiming at reducing turbulence interaction noise of an isolated airfoil studied in the framework of
European project FLOCON. First calculations on baseline conditions are shown to be able to reproduce the
measured spectra and far-field directivities, and the acoustic performances of the serrations (3-4 dB PWL
reduction) are fairly well assessed too.

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