Considering the potential application environment properties of titanium alloy honeycomb acoustic liner

an experimental method of the acoustic test of the annular acoustic liner with the influence of temperature gradient was proposed

and a simulated engine aft-fan duct acoustic test rig was developed. Then the acoustic test on titanium alloy annular acoustic liner was carried out. In view of the noise of 2 500 Hz and 2nd-order circumferential mode and the grazing flow with Mach number of 02

a titanium alloy annular acoustic liner was designed and prepared. The acoustic characteristics of the titanium alloy annular acoustic liner were studied by the means of duct acoustic mode test and far-field directivity test

respectively. Results showed that the noise reduction of the designed titanium alloy liner in the duct was 319 dB under the target operating conditions

and the 1 m far-field noise reduction appeared to be over 20 dB between 30° to 120°. Increasing the velocity of grazing flow expanded the bandwidth of the noise reduction spectrum and shifted the peak value of the spectrum from low frequency to high frequency. Increasing the temperature of the backplane of liner had little effect on the bandwidth of noise

but it shifted the peak value of noise reduction spectrum from low frequency to high frequency.