Prediction of Air Flow Noise in Ducts due to the Presence of Fixed Obstacles

Regular paper

Nicolas Papaxanthos

Université de Technologie de Compiègne

Wednesday 3 june, 2015, 16:00 - 16:20

0.3 Copenhagen (49)

The work deals with the noise produced by the interaction of a low Mach number flow with fixed obstacles inserted in a rectangular duct. Such a study is necessary for noise control in most HVAC applications and, in particular, for automotive air conditioning systems. The computation of flow noise is accomplished following a hybrid approach. First, the results of a CFD simulation using unsteady incompressible LES are compared with measurements using particle image velocimetry systems. The procedure allows to compare the mean flow velocities in the three directions as well as the turbulent kinetic energy. Second, the radiated acoustic pressure is calculated via the Lighthill’s acoustic analogy using different integral formulations. One is based on the fluctuating drag forces acting on the obstacles. The other one requires the knowledge of the aerodynamic pressures on all surfaces including the duct. This latter, though more demanding from a computational point of view has the advantage of being applicable to any arbitrary geometry and permits to take into account the diffraction effects taking place in the duct. The case of a constriction such as a diaphragm is investigated in details. Noise spectra obtained with the two integral formulations are compared with measurements using an active 2N-port model for flow generated noise.

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