Hydrodynamic interference in corrugated pipe whistling

Corrugated pipe whistling is mainly controled by the synchronisation of vortex shedding at each cavity by global acoustic standing waves, pipe modes. The vortex shedding of one cavity can however interfer with the vortex shedding of the next cavity. Such constructive, as well as destructive, interference has been demonstrated for a tandem of two cavities. The significance of this phenomenon is studied for corrugated pipes. The whistling of three pipes with 32 cavities differently distributed over equal total pipe length has been measured. While there is a clear indication for constructive hydrodynamic interference for pipes with sinusoidal corrugations, the results are also affected by the difference in cavity distribution over the standing waves. An acoustical velocity is needed to generate sound. The cavities do not produce sound when placed close to a pressure anti-node. In order to clarify the hydrodynamic interference numerical URANS simulations have been carried out. These indicate a quite significant constructive hydrodynamic interaction.