In the study of flow oscillation and discrete frequency noise of impinging jet, it is found that there is a critical pressure ratio for a given nozzle and a nozzle-to-plate distance.

为探索冲击射流离散频率噪声的产生机理，系统地研究了冲击射流离散频率噪声的特性。

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The filter processes input discrete sampling signal to recover continuous signal and suppress harmonic noise, and the zero-crossing frequency measuring method is improved.

该滤波器通过处理输入离散采样信号获得连续信号并抑制谐波噪声，改进了过零测频方法。

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A concept and a numerical formula of flowing velocity on many blades are presented to discuss noise in the discrete frequency.

为了讨论离散性频率噪声，本文提出了多叶叶道流速激发的概念和计算公式。

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