Onset of flow induced tonal noise in corrugated pipe segments

Corrugated pipes combine small-scale rigidity and large-scale flexibility, which make them very useful in industrial applications. The flow through such a pipe can induce strong undesirable tonal noise (whistling) and even drive integrity threatening structural vibrations. Placing a corrugated segment along a smooth pipe reduces the whistling, while this composite pipe still retains some global flexibility. The whistling is reduced by thermoviscous damping in the smooth pipe segment. For a given corrugated segment and flow velocity, one would like to predict the smooth pipe length just sufficient to avoid tonal noise: the onset of whistling. A linear model based on empirical data is proposed that predicts the conditions at the onset of whistling for a composite pipe at moderately high Reynolds numbers, Re: 3000 < Re < 100,000. Experimental results for corrugated pipes of eight different corrugation geometries are presented revealing fair agreement with the theory. Based on these results, a universal qualitative prediction tool is obtained valid for corrugated pipe segments long compared to the acoustic wave-length.