Numerical Simulation Of Air-Modulated Speaker With A Time-Dependent Shape Vocal Tract Model

As a typical high-power and high-pressure pneumatic speaker, the air-modulated speaker occupies an important position in researches about the high-intensity acoustic wave and its effects. With the development of applications, it is hoped to further improve the performance of the air-modulated speaker. It is generally believed that the energy conversion mechanism of the air-modulated speaker is similar to that of human vocal organs, since both processes can be attributed to the air-modulated problem. During human phonation process, the time-dependent shape of the glottis influences the flow field and acoustic energy conversion obviously. It is different from the orifice in the traditional air-modulated speaker, which moves like a valve. Based on the general CFD software FLUENT, two numerical simulation models were established in this paper. Their orifices were similar to the glottis during human phonation and the orifice in the usual air-modulated speaker, respectively. The flow field evolution and acoustic energy conversion under different working conditions were investigated. The main contents and conclusions of this paper include:1. Taking Meyer's rigorous theory and Maa's approximate theory as example, the solution of the classical quasi-steady theory was analyzed. The analysis provided some useful guidance for possible application of improving the acoustic characteristics of pneumatic speaker. Also the theoretical limitations due to the assumption were discussed.2. The numerical simulation models of pneumatic speaker with the time-dependent shape vocal tract and the orifice in the usual air-modulated speaker were established by using FLUENT, respectively. The work included the mesh generation, the division of boundary conditions and computational domain, the selection of turbulence model, the application of dynamic mesh, and key parameters settings.3. Based on the established simulation models, plenty of data were gained and a detailed analysis was carried out. The obtained results suggest that the main features of unsteady flow field for high-speed confined modulated jets include the vortex interaction and the phenomenon of alternating high and low pressure. Changing chamber pressure and modulated frequency can affect the flow and acoustic field differently. The limitation of the quasi-steady theory was verified. Different modulated modes do not influence the flow field evolution significantly, but greatly affect parameters in the region near the orifice.