Prediction of Air Flow Noise in Ducts due to the Presence of Fixed Obstacles
Regular paper
Université de Technologie de Compiègne
Wednesday 3 june, 2015, 16:00 - 16:20
0.3 Copenhagen (49)
Abstract:
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.