Mechanism of cutoff frequency of resonator tube in thermoacoustic engine

Based on waveguide theory method, the cutoff frequency of a resonator tube in the thermoacoustic engine was investigated. A calculating model was established. Computation of the cutoff frequency of the circle and rectangular waveguide with the same equivalent radius was carried out, and the computation results were compared. The results show that the cutoff frequency of the rectangular waveguide tube with the same equivalent radius is far greater than that of the cylindrical tube. For thermoacoustic resonator with the equivalent radius of 2 mm, the work frequency of 5500 Hz is far smaller than the cutoff frequency of 50248 Hz at the sound velocity of 343 m/s, so only one dimension plane wave can be spreaded in the cavity of the thermoacoustic resonator. Calculating and analyzing results show that cutoff frequency method is an effective approach for the prediction frequency range of one dimension plane wave in thermoacoustic resonator.