A study of non-linear acoustic flows at the open end of a tube using particle image velocimetry

• Main Author: Skulina, David John
• Format: Dissertation
• Language: English
• Published: University of Edinburgh 2005

The radiation of sound from the open end of a resonant tube is relatively well understood at low acoustic amplitudes in terms of linear acoustics. At high acoustic amplitudes, however, additional non-linear loss mechanisms such as vortex shedding and jet streaming are known to affect the sound field at the open end and the efficiency with which a standing wave is maintained within a tube. This has implications in a number of fields, notably in musical instrument design and in the automotive industry. Particle Image Velocimetry (PIV) is used to acquire full-field instantaneous velocity information of the acoustic particle velocity field at the open end of a cylindrical tube in which a high amplitude should field has been generated by a loudspeaker. Five different tube terminations are used to examine the effect of varying the geometry of the open end on the flow phenomena observed. A qualitative identification of number of flow regimes is made and a number of techniques are used to evaluate the non-linear losses numerically. PIV results are used in combination with pressure measurements to evaluate the termination impedance and a comparison is drawn with results made by conventional methods. Jet streaming is investigated and the associated energy dissipation is estimated. Vortex sound theory is then used to measure the acoustical losses caused by boundary layer separation and the resultant generation of vortex structures.