The study deals with nonlinear acoustical effects localised at the open-end of a cylindrical tube. The termination impedance is measured using a two microphone method. Due to the separation of the acoustic flow at the pipe end, the real part of the termination impedance depends on the volume velocity at the open end. It is shown that the radius of curvature of the edges of the open end of the tube has a crucial influence on the amplitude of the nonlinear losses. Several regimes are shown for the low radii of curvature. c 2003 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS acoustics / wave guide / radiation impedance / nonlinearity
Impédance terminale d'un tuyau cylindrique ouvert à fort niveau sonore
Résumé. L'étude porte sur les effets acoustiques non-linéaires localisés à la sortie d'un tube cylin-drique. Des mesures de l'impédance terminale réalisées à l'aide d'une méthode à deux microphones montrent que les pertes -partie réelle de l'impédance terminale -augmentent avec la vitesse moyenne en sortie de tube. L'importance de ces pertes dépend fortement du rayon de courbure des bords intérieurs à la sortie de tube. Les pertes peuvent être interprétées comme la conséquence de la séparation de l'écoulement acoustique en sortie de tube. Pour les faibles rayons de courbure, plusieurs régimes sont mis en évidence.
At high acoustic level, non-linear losses at the end of a tube are usually interpreted as the consequence of a jet formation at the tube end resulting in annular vortices dissipating part of the acoustic energy. Previous work has shown that two different regimes may occur. The present work, using particle image velocimetry visualization, lattice Boltzmann method simulation in 2D, and an analytical model, shows that the two different regimes correspond to situations for which the annular vortices remain attached to the tube (low acoustic particle velocity) or detached (high acoustic particle velocity).
The question of what limits the amplitude of the oscillations of clarinet-like instruments is investigated. The study is based on numerical simulations in which two kind of losses are taken into account: linear losses and non-linear losses localised at the open end of the tube. The influence of the amount of losses on the saturation process and on the playing range of clarinet-like instruments is shown. Results are confirmed by experiments using an artificial mouth in which the non-linear losses are varied using several terminations with different geometries.
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