Numerical Assessment of Open-Rotor Noise Shielding with a Coupled Approach

Abstract

In this work, scattering and shielding of the tonal noise from contrarotating open rotors by surrounding parts are investigated. The computational tool chain is based on unsteady Reynolds-averaged Navier–Stokes simulations providing permeable integration surface data for a Ffowcs Williams and Hawkings-type evaluation (“Sound Generated by Turbulence and Surfaces in Arbitrary Motion,” Philosophical Transactions of the Royal Society of London, Series A: Mathematical and Physical Sciences, Vol. 264, No. 1151, 1969, pp. 321–342), which is coupled with a fast multipole boundary-element method to account for shielding by the airframe. The effect of a background mean flow is taken into account by applying a Lorentz transform to the boundary-element problem and using the Möhring analogy instead of the Ffowcs Williams and Hawkings formulation to obtain the incident acoustic field. Validation of the Möhring/boundary-element coupling method is shown on the basis of a model contrarotating open rotor with shielding geometries and a mounting pylon. The tool chain is then applied to a full-scale open-rotor engine installed in different aircraft tail configurations (T tail, L tail, and U tail) to assess their influence on flyover and lateral noise in takeoff conditions.