In order to investigate the characteristics of engine intake fan noise and the noise reduction effect of acoustic liner

the intake fan noise was provided by a mode generator. The noise signal inside the intake was measured by using a fixed microphones array and a rotating microphones rake

and then the amplitude of acoustic mode inside the intake was determinated by using circumferential and radial mode decomposition method. The key factors affecting the results of mode decomposition were investigated. The circumferential mode was decomposed in time domain

and the time-resolved characteristics of amplitude and phase were obtained. Finally

the noise reduction effect of two acoustic liner samples was experimented. The results showed that: the main mode characteristics of fan noise could be obtained by the mode generator

including the mode amplitude and the rotating angular velocity; under the condition of satisfying the sampling theorem

the main mode produced by the mode generator was independent of the numbers of loudspeakers in the case of n=0; the influence of the numbers of sampling position of the rotating microphones rake on the results could be ignored if using the rotating microphones rake to measure the acoustic mode; and at the design frequencies

the acoustic liners had good noise reduction effect. It is concluded that: the intake fan noise source provided by the mode generator can be used for further experimental verification of acoustic liner design method.