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SYNCHRONIZED VORTEX SHEDDING AND SOUND GENERATION IN A CORRUGATED PIPE : A GLOBAL STABILITY APPROACH

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Corrugated pipes, such as gas hoses or electrical sheaths, are objects which combine a local rigidity and global flexibility, and are thus largely used in a number of engineering applications. At critical conditions, the flow through such a pipe can produce a loud whistling sound. This phenomenon is undesirable in industrial application because it can result in strong mechanical vibration and damage to the structure. On the other hand, the phenomenon is also at the origin of a musical toy called the "hummer" (sometimes also described as "the voice of the dragon") in which the flow is produced by centrifugal effect when swirling the pipe above one’s head. The mechanism responsible for such a whistling has made the object of recent experimental and numerical studies. The origin of the mechanism lies in a coupling between vortex shedding occurring in a periodic way above the cavities which constitute the wall of the pipe, and an acoustic standing wave. The latter has the effect of stimulating the emission of vortices in a synchronized way, which in turn provide energy to the acoustic wave. The whole phenomenon can thus be described as a SASER (for "Sound Amplification by Stimulated Emission of Radiation"). Since the wavelengths
corresponding to the acoustic part of the flow are much larger than the size of the corrugations, the flow at the scale of a single (or a few) cavities can be assumed, as a first approximation, to be incompressible. A recent experimental and numerical study has explored the interaction between adjacent cavities, and has shown that depending on the cavity
spacing, the interaction can be constructive (when vortices are shed in a synchronized way) or destructive (when vortex shedding occurs with a phase opposition between adjacent cavities). The objective of the present work is to investigate such couplings using a global stability approach of the flow at the size of the cavities.

Author(s):

[CANCELLED]    

Serena Russo    
Dipartimento di Ingegneria Industriale (DIIN), Università di Salerno
Italy

Flavio Gianneti    
Dipartimento di Ingegneria Industriale (DIIN), Università di Salerno
Italy

Paolo Luchini    
Dipartimento di Ingegneria Industriale (DIIN), Università di Salerno
Italy

David Fabre    
Institut de Mécanique des Fluides de Toulouse (IMFT), Université de Toulouse
France