Control of flow induced vibrations by means of resonators

This paper focuses on flow-induced acoustic vibrations in piping with closed side branches. These self-sustained oscillations can be very violent, causing an unpleasant or harmful noise. In addition, serious mechanical damages to the pipe supports are possible, due to the consequent mechanical vibrations. Since it is often impossible to completely avoid the problem, it is necessary to resort to strategies in order to mitigate its effects, or by shifting the operating conditions in which they can occur towards different frequencies. This paper deals with the possible use of Helmholtz resonators applied to side branches in order to attenuate noise or to shift the dangerous conditions of resonance. A numerical model is used to study the response of the system in the frequency domain. Initially a side branch with a standard resonator is simulated to highlight the physical phenomena and to study the influence of the main parameters (geometry and position of the resonator). Then some modifications of the simple resonator are proposed in order to increase the dissipation effects in the neck and improve the attenuation of the acoustic vibrations. In particular, the effect of a helical shaped neck and of a composite neck made up of a bundle of narrow ducts is shown. Finally, the potentialities of a double resonator are investigated.