A parametric study on the whistling of multiple side branch system as a model for corrugated pipes

Corrugated pipes are widely used in industry due to their inherent character of being globally flexible and locally rigid. Under certain conditions flow through the corrugated pipes causes severe noise and vibration problems. Thus, to understand the phenomenon and parameters that play role is a real asset for industry. This study is a continuation of a research based on multiple side branch system and presented together with results of an investigation performed on corrugated pipes. Many similarities between the corrugated pipes and multiple side branch system have been observed. A Strouhal number which uses as characteristic length the cavity width plus the upstream edge radius yields the best collapse of the data for both corrugated pipes and multiple side branch system. For both systems the upstream edge radius of the cavity has significant effect on pressure fluctuation amplitudes. It can increase the amplitude of the pressure fluctuation by an order of magnitude compared to sharp edges. The radius of the downstream edge has a less pronounced effect on the sound production. Strouhal numbers display two hydrodynamic modes the first with a Strouhal number around 0.1 and the second one varying in the range between 0.4 and 0.6. The variation in critical Strouhal number for the second hydrodynamic mode correlates with the relative corrugation volume compared to the pipe volume. Experiments with corrugated pipes reveal that 1st hydrodynamic mode is limited to configuration with small relative corrugation volume. The first hydrodynamic mode was not yet observed in the multiple side-branch systems.