The accordion reed is an example of a blown closed free reed. Unlike most of oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the temporal domain. The excitation force is foud to be associated with the intertial load of the upstream fluid. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernouilli force. A pressure component generated by the local reciprocal air movement around the valve is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near field of the reed is reasonable. In addition, an aeroacoustic model using the porous Ffowcs Williams-Hawkings integral method is presented. The integral expressions of the far field acoustic pressure are also computed in the temporal domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong fluid velocity fluctuations in the plane of the reed.
Article paru dans : Journal of Acoustical Society of America