Second Paper: Lateral Helmholtz Resonator Silencer with Turbulence Absorption

Abstract

Lateral Helmholtz resonators are ineffective for fast flow because of the turbulence caused by the movement of the gas mass from the resonator neck into the main pipe flow. The absorption of this turbulence at its source is an effective method for keeping the resonator silencing ability at a high level. Experimental results on an acoustic filter formed by resonators for flow velocities up to 80 m/s, so treated, are compared with the theory. There is evidence of lateral resonance of the gas column in the exhaust pipe at high flow velocities, detected as an intense noise of a discrete frequency (1000 Hz). The excitation of this resonance was found to be due to the pseudo-acoustic wave caused by the neck jets in the resonator. The influence of the flow upon the natural frequency of the resonator is also discussed. The Reynolds number of the flow seems to play an essential role on this point.