Particle image velocimetry measurement and vortex sound analysis of high-amplitude acoustically generated flows in open ended tubes

Abstract

Periodic vortex shedding induced by an acoustic field has been observed by several authors at orifices and at the open ends of tubes. It is a well-known dissipative mechanism and affects the sound field at the open end of a tube and the efficiency with which a standing wave can be maintained within it. This has obvious implications in the playability and design of musical wind instruments. To quantify the losses associated with vortex generation and shedding at the open end of a tube a method for the evaluation of PIV velocity maps using vortex sound theory is outlined. Comparison between the results of the vortex sound calculations and the velocity fields measured from the PIV vector maps allows both qualitative and quantitative descriptions of the acoustical effect of vortex shedding on losses over the acoustic cycle. It is found that the net acoustical losses due to the interaction of vortices with the acoustic field are most significant in a region within 2.5 mm of the open end. Out of this region, vortices act as a net source of sound, but are of lesser magnitude. [Work supported by EPSRC.]