Structural/acoustic interaction in air-conditioning ducts in the presence of mean flow

The finite element method is applied to the modelling of noise breakout from air-conditioning ducts which are rectangular in cross-section and lined with a bulk reacting sound absorbent. Mean flow in the central airway is also included in the model. An eigenvalue formulation is employed to couple the acoustic pressure field inside the duct to the displacement of the duct walls. Numerical predictions for the axial wavenumbers of the first “structural” and “acoustic” modes are examined both with and without mean flow