Corrugated pipe segment with anechoic termination: critical Mach number for whistling

Corrugated pipes combine local stiffness with global flexibility, which makes them very useful. A drawback of corrugated pipes is the whistling, which results from coupling of vortex shedding with acoustic plane waves due to the flow through the pipe. We consider the possibility to reduce whistling by placing a short corrugated pipe segment along a long smooth pipe. A linear model is proposed in which the magnitude of the dipolar sound source is determined empirically. The model allows to estimate the critical Mach number of the flow through the pipe above which the whistling will always occur even for anechoic pipe terminations.