Broadband Acoustic Liner Design and Verification of Helmholtz Resonators with Extended Necks
In order to reduce the noise of low frequency fan of turbofan engine with large bypass ratio,the acoustic liner that can absorb the low-frequency broadband noise was studied,and its sound absorption performance was verified.The acoustic liner is composed of Helmholtz resonators with extended necks,and the structural parameters of the resonators are different.By coupling the resonators with different parameters,the sound liner can absorb noise with wider frequency band.Firstly,the surface acoustic impedance model of the Helmholtz resonator with extended neck is established according to the transfer matrix theory.On this basis,a prediction model for the sound absorption performance of the coupled non-uniform acoustic liner is established.Then,based on this model,the average absorption coefficient of broadband noise is taken as the objective function,and the parameters of the Helmholtz resonator are inverted by using particle swarm optimization algorithm to find the optimal parameters of the Helmholtz resonator for this band of noise.Finally,the traditional sound liner with a frequency of 950 Hz and the broadband acoustic liner sample with a frequency band of 800-1 000 Hz are prepared,and their sound absorption performances are measured and compared through experiments.It is shown that results of the test of the broadband acoustic liner is consistent with those of the prediction,which confirms the validity of the prediction model and the accuracy of the optimization results.Compared with the bandwidth with the sound absorption coefficient greater than 0.8,the bandwidth of the traditional acoustic liner is 100 Hz,and the broadband acoustic liner is 230 Hz.The sound absorption band of the broadband acoustic liner is widened by 113%.
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