| Popis: |
A method for predicting acoustic pressure radiated by a duct opening with internal axial flow, based upon mixed experimental and numerical tools, is presented. It is applied to a six‐bladed/one stator configuration axial fan cowled by a cylindrical duct 2.3 m long, 0.6 m in diameter and carrying a low‐speed axial flow (M0≤0.1). Experimental mappings of acoustic pressure, acoustic axial particle velocity, and axial mean flow velocity at blade passing frequencies upstream of the rotor are carried out using a probe made of a microphone and a single hot wire. The results show an acoustic field structure as expected by acoustic propagation laws in ducts. After a modal filtering, experimental radial acoustic potential profiles are input to the database for the prediction process. In the second step, the theoretical radiated far field is computed using a program based on a variational formulation by integral equations accounting for internal flow. The very good agreement between theoretical and experimental resu... |
