Numerical model research for the sound energy conversion in air-modulated speaker

The numerical model of air-modulated speaker(AMS)based on the hybrid computational aero-acoustics (CAA)method is proposed to overcome quasi-steady theory limitation in high frequency and low chamber pressure conditions and provide analysis tool to relate engineering designs with characteristics in radiation field.Characteristics in both fields at typical working condition are analyzed.Frequency dependence in energy conversion process is emphasized. The internal flow of AMS is described by unsteady Reynolds-averaged Navier-Stokes(RANS)equation,shear-stress transport(SST)κ-ωturbulence model is coupled with enhanced wall treatment to predict flow separation in the vocal tract,the dynamic mesh technique is utilized for modeling of voice coil modulation,and porous Ffowcs Williams and Hawkings(FW-H)integral is used for near field acoustic calculation.Primary parameters are properly selected in compressible flow,dynamic mesh,near-wall mesh generation,boundary condition,and acoustic analogy to make unsteady flow and acoustic field accurate.Agreement in steady flow is obtained between simulation and experiment results. Predominant frequency in acoustic signal is basically consistent with modulated function,and harmonic components due to nonlinearity are evident.Compared to the low frequency case,vortex evolution and free shear layer presence make dipole and quadrupole sources unable to be neglected in corresponding acoustic field prediction.