Aerodynamically generated acoustic resonance in a pipe with annular flow restrictors

An experimental study of the coupling between fluid dynamic instabilities a nd an acoustic held is performed for the case of a pipe with annular flow r estrictors, representing a segmented solid propellant booster. As long as t he distance between the restrictors remains smaller than the length of the how recovery region behind the upstream restrictor, the fluid flow can ampl ify the acoustic pereturbations at the frequencies of the acoustic modes,le ading to strong resonance for specific flow velocity ranges. A physical exp lanation is proposed, linking the amplification of the acoustic perturbatio n to the phase and frequency of vortex shedding from the restrictors. An ap proximate semi-empirical correlation is developed for the critical Strouhal number of the phenomenon as a function of the restrictor size and other pr oblem parameters. (C) 1999 Academic Press.