Abstract
Parallel triangle tube arrays with pitch ratios in the range of 1·2–4·2 have been tested at Reynolds numbers up to 9×104to investigate the vorticity shedding and acoustic resonance mechanisms. Three different components of flow periodicities have been observed. The flow periodicity with the highest Strouhal number (S3) is the weakest component. It is caused by a shear-layer instability in small pitch ratio arrays and at low Reynolds numbers. The S2component is associated with small-scale vortex shedding at the first row. The third component has the lowest Strouhal number (S1) and is the strongest. It is generated by large-scale, alternating vortex shedding at deeper rows, and it becomes dominant at all rows at high Reynolds numbers. For tube arrays with pitch ratios less than 3·4, the onset of acoustic resonances could not be related to the natural flow periodicities mentioned above. This behaviour is in contrast with that of normal triangle arrays, but similar to the acoustic behaviour of in-line arrays. Strouhal number charts for the natural flow periodicities and for the onset of acoustic resonances have been developed.
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