Acoustic data measured in a fan test facility with and without an inflow control device (ICD) over the inlet were analyzed using the cyclostationary analysis technique, which separates the total power into a rotor-locked and a fluctuating component. Measurements were taken with an inlet mode detection ring upstream of the rotor and with far-field microphones for configurations with subsonic and with supersonic fan blade tip speeds. The ICD reduces the fluctuating component and stabilizes the rotor-locked component of the frequency spectrum at the blade passing frequency and its harmonics in the way that the mode amplitudes of the Tyler–Sofrin modes increase, whereas neighboring mode orders are suppressed. The mode distribution and intermode coherence in the inlet are also changed, which changes the far-field directivity when an ICD is installed. It is demonstrated that cyclostationary analysis is a powerful tool to investigate the acoustic effect of an ICD on turbofan noise, revealing more details about the temporal and spatial structures of the generated sound field than a classical spectral analysis.

使用循环平稳分析技术来分析在风扇测试设备中测量的声学数据，该测试设备带有或不带有进气控制装置（ICD），该技术将总功率分为转子锁定组件和波动组件。使用转子上游的进气口模式检测环和远场麦克风进行测量，以实现亚音速和超音速风扇叶片叶尖速度的配置。ICD减小了波动分量，并在叶片通过频率及其谐波处稳定了频谱的转子锁定分量，从而使Tyler-Sofrin模的模振幅增加，而相邻模的阶被抑制。入口中的模式分布和模式间相干性也会发生变化，这会在安装ICD时改变远场方向性。