Multimodal Method for Flow-induced Acoustic Resonance in Successive Deep Axisymmetric Cavities in a Duct
Regular paper
LAUM
Wednesday 3 june, 2015, 09:40 - 10:00
0.3 Copenhagen (49)
Abstract:
Acoustic pulsations in axisymentric cavities in a flow duct have been observed
in
many engineering applications, such as gas transport systems and aeroengines.
The
pulsations result from the coupling between the hydrodynamic instabilities of
the
shear layer emanating from the upstream edges of the cavities and the cavity
acoustic modes, through a feedback loop. Both the sound amplification and the
self-excited tones that are directly related to flow-induced pulsations have
been
reported. In some cases, the resonance modes are trapped in the cavities, thus
exhibit zero radiation losses and produce significantly high-level pressure
pulsations. Therefore, the flow-induced pulsations are undesirable because of
the
noise emission and the probable fatigue issues.
The objectives of the present work are to predict the pulsations in a
cavities-
duct configuration, to study the coupling mechanism between the shear layer
and
the acoustic modes in detail, and to demonstrate the effects of the
interaction
between adjacent cavities. It is also believed that the results help to cast
light
on new control strategies of the pulsations.
The numerical model is established based on the multimodal method, in which
the
radial modes of 2D cylindrical duct segments are solved. Matching the modes at
the
interfaces between the segments gives the reflection and transmission
coefficients
of the cavities-duct system, showing the coupling state of the shear layer and
the
acoustic modes. The numerical results are also compared with the experimental
results.