An acoustic design method for nacelle exhaust duct acoustic liner is proposed based on the application environment of exhaust duct acoustic liner. An acoustic impedance parameter optimization model of exhaust duct acoustic liner is established using the finite element method. According to the design conditions and structural constraints, we design and prepare a set of full-scale exhaust duct inner wall acoustic liner simulation test pieces. To verify the acoustic design method for the exhaust sound liner, a full-scale sound liner acoustic test platform with a frequency range of 500-16 000 Hz and a maximum circumferential 15th order mode is developed to simulate the noise characteristics of fan back propagation. The directivity tests at 3 m and 5 m downstream of sound propagation under the sound liner and solid wall conditions are performed, respectively, and the noise reduction in the range of 500-1 500 Hz is obtained. The test results show that the optimal noise reduction effect of the designed sound liner is reached at the frequency of 950 Hz and 1 000 Hz, fully verifying the accuracy of the acoustic liner design. The sound pressure level distribution of the directivity of the radiated sound field at 3 m and 5 m of the sound liner under the design condition is analyzed, and the test results show the maximum noise reduction in the range of 0°-90° being 10.44 dB and 7.21 dB, respectively. The proposed acoustic design and verification method for exhaust duct acoustic liner can provide important technical support for the design and verification of exhaust duct acoustic liner of engine nacelles in China.
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