Analytical Prediction of Wake-Interaction Noise in Counter-Rotating Open Rotors

An analytical methodology for the prediction of tonal Counter-Rotation Open Rotor wake- interaction noise is presented. Unsteady loadings on the blades are obtained from an ex- tension of Amiet's theory for gust-airfoil interaction accounting for airfoil sweep and chord variations in the span-wise direction. The far-field sound is formulated in the frequency domain from the generic formula of acoustic dipoles rotating in a uniformly moving atmo- sphere, according to Ffowcs Williams & Hawkings' analogy. The expression includes the effect of dipole radial component and blade camber on noise radiation. The methodology is assessed by comparison with URANS results and wind-tunnel measurements.