哑铃形热声谐振器的谐振频率

Thermoacoustic resonant frequency of a dumbbell resonator

热声自激振荡模态取决于声学谐振器结构形式和特征尺度。级联型热声热机依靠哑铃形谐振器来调制所需要的局部高阻抗行波声场,谐振管通常由几段不同横截面的管段组成。哑铃形热声谐振器的谐振频率由共鸣腔容积、谐振管截面和长度共同决定。根据哑铃形谐振器不同截面管段内的声传播规律、共鸣腔声学边界条件以及管段间的声压和体积流率连续条件,利用行波叠加的方法,建立均匀管模型、变截面模型和热声网络模型,得到了系统谐振频率随共鸣腔容积变化和谐振管特征尺寸变化的规律。系统谐振频率的变化将引起最佳听音点的位置的移动,进一步起到调节回热器声阻抗的作用。实际热声热机实验研究中,通过改变谐振器特征尺度或结构形式调节系统的谐振频率,也是热声热机调试过程中实现自激振荡的主要手段。

The resonant mode of thermoacoustic self-exited oscillation is determined by the configuration and character dimensions of acoustic resonators. Cascade thermoacoustic devices use a dumbbell resonator to modulate a local traveling wave sound field with high impedance. Thermoacoustic resonant tube is often consisted of several segments with different sections. The cavity volume, tube sections and the tube length determine the resonant frequency of a dumbbell resonator. According to the propagation rule in resonant tubes, the acoustic boundary condition and the condition of continuous volume velocities at the interfaces of different sections, a uniform tube model, a varying section tube model and a thermoacoustic network model are all built and discussed. These models reveal how the resonant frequency varies when the characteristic dimensions of the resonator vary. The regenerator impedance would be adjusted by the sweet spot transfer due to the change of resonant frequency. It is also an important way to realize self-exited oscillation in experiments of thermoacoustic engines by changing the characteristic dimensions or configuration of the resonator.