LAUSR

Abstract The present work is aimed at illustrating a hybrid analytical/numerical methodology that could be used at the early-design stage to predict the tonal noise of an axial-flow fan surrounded by solid surfaces. A model shrouded helicopter tail-rotor architecture is selected as a typical example of unconventional rotor-stator stage. The advanced design involves uneven rotor-blade spacing and leant stator vanes, one of which is replaced by the transmission shaft. Both the rotor and the stator generate tonal noise at the same frequencies, because of the potential distortion around the shaft and because of the impingement of the blade wakes on the vanes, respectively. Source-modes made of circular distributions of stationary sources properly phase-shifted are introduced to reproduce all sources in a unified way, based on analytical expressions. This part is based on simplified unsteady aerodynamic theories. The source-modes are then used as input in a numerical software solving the Helmholtz equation to assess the sound scattering by the shroud. The approach is applied only to the stator noise for illustration and typical results are discussed.