3D CAA methodology using synthetic turbulence to assess turbulence-cascade interaction noise emission and reduction from serrated airfoils

International audience; The context of this study is the development of innovative stator concepts to reduce noise from rotor/stator interaction in future high bypass engines. Leading edge serrations are examined using a hybrid CFD/CAA method. A stochastic approach is considered for the turbulence generation based on a Fourier modes decomposition. A methodology to obtain a fully 3D turbulence field, while taking into account periodic and wall boundary conditions is developed and a formulation is finally provided to obtain a perfectly incompressible stochastic field. The influence of the turbulence structure on far-field acoustic spectra is first discussed for the baseline computation case. In a second step, numerically assessed noise reductions from the serrated design are favorably compared with an analytical solution and a semi-empirical law. An overall sound power level reduction around 4 to 6 dB is obtained at three acoustics certification points. Finally, the aerodynamic performances of the serrated airfoil are evaluated through RANS computations and an improved variant of the initial design is proposed, allowing for acceptable penalties at the aerodynamic design point.