Fan Noise Reduction by Cascade Clocking for Next Generation Supersonic Transport

叶栅计时是一种通过适当调整下游静叶相对于上游静叶的圆周位置来降低多级轴流压气机总压损失的概念。首席调查员发现，在多级风扇的情况下，相同的概念可以应用于降低风扇的音调噪声，例如用于下一代超音速运输的推进系统，其中风扇旁路比相应地低，风扇压力比高，并且需要两级或三级风扇。为了将叶栅计时概念应用于音调降噪，对于多级，转子叶片的数量应该相同，并且定子叶片的数量也应该相同。然后，对于多个阶段，音调频率相同，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级产生的音调的压力波的可能性本项目的目的是通过实验验证叶栅计时概念降低音响噪声的可能性，并从数值上找出叶栅计时优化的条件。实验采用了一台两级轴流压缩机，第一级和第二级有32个转子叶片，两级都有38个静叶。它具有定子叶片连续计时和转子叶片每隔1/8螺距计时的能力，结果表明，定子叶片计时可使音调噪声降低18分贝。对于两级的固定转子叶片设置，降噪程度取决于压缩机的转速。然而，动叶计时和定子叶片计时相结合可以给出上述最大的减振效果。数值计算很好地解释了实验得到的音调噪声水平随级联时钟变化的规律。较少

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