Aeroacoustic near-field study of a ducted helicopter tail rotor with different vane count by use of phase-lagged boundaries

A numerical study of the aeroacoustics for a ducted helicopter tail rotor with 3 different vane numbers is presented. Computations were carried out under hover flight conditions. The reference geometry incorporated 10 rotor blades and 11 stator vanes. Additionally, a configuration with 7 vanes and a 19-vaned configuration, which should be favourable in terms of the cut-off condition of the 1st harmonic, were analysed. The investigated stage was modelled as single passage, whereas phase-lagged boundary conditions were used in order to take the exact blade ratio into account. To obtain the unsteady flow field as well as the acoustic near-field the fully turbulent, three-dimensional, Favre averaged Navier-Stokes (FANS) equations that were solved on a structured multi-block mesh using the flow solver TRACE. In addition to global parameters (e.g. thrust and shaft-power), the study aims to determine the differences in stage acoustics due to the variation of the vane count.