Numerical Assessment of CROR Noise Shielding with a Coupled Mohring Analogy and BEM Approach

摘要

In this work, scattering and shielding of the tonal noise from contra-rotating open rotors (CROR) by surrounding parts is investigated. The computational tool chain is based on unsteady Reynolds-averaged Navier-Stokes (URANS) simulations providing permeable hull surface data for a Ffowcs Williams and Hawkings (FWH) type evaluation, which is coupled with a Fast Multipole Boundary Element Method (FM-BEM) to account for shielding by the air-frame. The effect of a background mean flow is taken into account by applying a Lorentz transform to the BEM problem and using the Mohring analogy instead of the FWH formulation to obtain the incident acoustic field. Validation of the Mohring/BEM coupling method is shown on the basis of a model CROR with shielding geometries. The tool chain is then applied to a full scale CROR 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.