Multimodal Method for Flow-induced Acoustic Resonance in Successive Deep Axisymmetric Cavities in a Duct

Regular paper

Xiwen Dai


Wednesday 3 june, 2015, 09:40 - 10:00

0.3 Copenhagen (49)

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.

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