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Non-linéarité acoustique localisée à l'extrémité ouverte d'un tube. Mesure, modélisation et application aux instruments à vent.

Abstract : The study deals with localised non-linear acoustic losses at the open end of a tube. Three aspects are considered: firstly, a description of the phenomenon by the measurement of the terminal impedance of the tube, secondly, the physical modeling of the phenomenon and finally the application to woodwind instruments.

In a first part, measurements of the terminal impedance using a two microphone method show that losses at the open end of the tube --- real part of the termination impedance in the first harmonic approximation --- increase with the acoustical velocity amplitude. Results show that the losses highly depend on the radius of curvature of the tube's inner edges. Moreover, for low values of the radius of curvature, two behaviours are observed. Particle image velocimetry (PIV) visualisations carried out at the University of Edinburgh confirm these two behaviours: in both cases, a vortex ring is created at the open end but it stays in the vicinity of the exit for low acoustical velocities whereas it is expelled for higher acoustical velocities.

The second part deals with the physical modeling of the phenomena. The application of the vortex-sound theory allows a direct estimation of the losses at the open end. Three calculations using this theory are carried out. The first calculation is analytical and is based on a discrete vortex ring which can be either fixed or mobile; the second one comes from PIV visualisations; and the third one is numerical, using the lattice Boltzmann method. The three calculations lead to similar results: non-linear losses find their origin in the formation of vortex rings at the end of the tube. These results are succesfully compared to impedance measurements.

The third part analyses the influence of non-linear losses on the behaviour of a side-holed wind instrument. Experiments and simulations show that the playing range of a wind instrument depends on the losses in the instrument and that the playing range can be extended by reducing the non-linear losses at the open end.
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Contributor : Mérouane Atig <>
Submitted on : Thursday, May 19, 2005 - 1:24:05 PM
Last modification on : Monday, October 19, 2020 - 11:06:14 AM
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  • HAL Id : tel-00009283, version 1

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Mérouane Atig. Non-linéarité acoustique localisée à l'extrémité ouverte d'un tube. Mesure, modélisation et application aux instruments à vent.. Acoustique [physics.class-ph]. Université du Maine, 2004. Français. ⟨tel-00009283⟩

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