Fan Noise Reduction by Cascade Clocking for Next Generation Supersonic Transport

叶栅时序是通过调节下游静叶相对于上游静叶的周向位置来降低多级轴流压气机总压损失的一种概念。首席研究员发现，在多级风扇的情况下，例如用于下一代超音速运输机的推进系统的情况下，可以应用相同的概念来降低风扇音调噪声，其中风扇涵道比低，风扇压力比高，并且需要两级或三级风扇。为了将级联时钟概念应用于音调噪声降低，转子叶片的数量对于多级应该相同，并且定子叶片的数量也应该相同。然后，音调频率对于多个阶段是相同的，并且音调的圆周模式变得相同。存在通过音调的压力波来抵消由第一阶段产生的音调的压力波的可能性 ...更多信息 本课题的目的是从实验上证实级联时钟的概念降低音调噪声的可能性，并从数值上找出级联时钟优化的必要条件。实验中使用了第一级和第二级具有32个转子叶片以及两级具有38个定子叶片的第二级轴向压缩机。它具有静叶连续同步和动叶每隔18节距同步的能力，静叶同步可使噪声降低18 dB。对于两级的固定转子叶片设置，降噪水平取决于压缩机的旋转速度。然而，转子叶片同步和定子导叶同步的组合可以给出上述的最大减少。数值计算很好地解释了音调噪声电平的变化对级联时钟的实验获得。少

Cascade clocking is a concept to reduce the total pressure loss incurred in a multi-stage axial compressor by adjusting properly the circumferential position of the downstream stator vane relative to the upstream stator vane. The head investigator discovered the fact that the same concept can be applied to reduce fan tone noise in the case of a multi-stage fan such as used for the propulsion system of the next generation supersonic transport where the fan bypass ratio is low accordingly, the fan pressure ratio is high and a two or three stage fan is required.In order to apply the cascade clocking concept to tone noise reduction, the number of rotor blades should be the same for multiple stages and also the number of stator vanes should be the same. Then, the tone frequency is the same for multiple stages and the circumferential mode of the tone becomes identical. There is a possibility to cancel the pressure wave of the tone generated by the first stage by the pressure wave of the tone … More generated by the second stage based on the principle of superposition.The purpose of this project is to confirm experimentally the possibility to reduce tone noise by the concept of cascade clocking and also to find out numerically the condition necessary for the cascade clocking to be optimized.A two-stage axial compressor having 32 rotor blades for the first and the second stages and 38 stator vanes for both stages were used for the experiment. It has the ability of stator vane clocking in continuous fashion and that of rotor blade clocking at every 1/8 pitch.Results show that stator vane clocking can reduce the tone noise by as much as 18 dB. The level of noise reduction depends on rotational speed of the compressor for a fixed rotor blade setting for both stages. However, the combination of rotor blade clocking and stator vane clocking can give the maximum reduction mentioned above. Numerical calculation well explains the tone noise level variation against cascade clocking as obtained by experiments. Less