Flow Induced Noise
The flow of gases past any cavity can lead to significant pressure pulsations and acoustic noise. For example, flow past dead-legs in a piping system or a recessed cavity in the fuselage of an aircraft or terrestrial vehicle, can lead to strong pressure pulsations leading to mechanical failure. This problem can become particularly severe when a feedback loop exists between the resonant system and the excitation phenomena, leading to lock-on and reinforcement of the fundamental excitation. Coanda has studied flow induced noise in various flow systems, designed passive and active spoilers, and mapped standing wave patterns in complex piping systems.
Shown here is an apparatus designed to measure the pressure amplitude at the closed end of a stepped dead-leg undergoing quarter-wave resonance induced by shear layer oscillation (D. Kiel and C. Foy, "Tone Generation in Stepped Side-Branches", INVC Conference Proceedings pp. 161-168, 1993)
Close end pressure amplitude data as a function of dead-leg geometry.
Aluminium inserts used to step down the diameter of the dead-leg from the main pipe section.