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Tip-timing accuracy improvement using optical fiber bundle probe with GRIN lens under varying blade tip clearance
Optical Engineering ( IF 1.3 ) Pub Date : 2021-11-01 , DOI: 10.1117/1.oe.60.11.114103
Fengyao Zhi 1 , Fajie Duan 1 , Zhibo Liu 1 , Xiuming Li 1 , Guangyue Niu 1 , Jiajia Jiang 1
Affiliation  

The blade tip-timing (BTT) method has become the industry standard in blade vibration measurement. It monitors blade vibration based on the different times of arrival (ToAs) between blade vibration and not. The optical fiber bundle (OFB) probe is widely used to obtain ToA because of its small size, fast response, and high tip-timing accuracy. ToA is usually obtained by comparing the received signal with a fixed threshold level. However, the varying blade tip clearance (BTC) will affect the received signal, which directly causes the tip-timing error. We propose an optical fiber probe with GRIN lens, which eliminates the tip-timing error caused by varying BTC through the constant-fraction discrimination (CFD) method. The model of the OFB probe with GRIN lens is first established. Model analysis indicates that ToA obtained by the proposed method is constant no matter how BTC changes. Finally, the accuracy of the model and the effectiveness of the method are verified by two experiments. When BTC varied from 1.5 to 3.5 mm, the maximum tip-timing errors of OFB probe without and with GRIN lens were 181.12 μs and 10.44 μs, respectively.

中文翻译:

在不同叶片尖端间隙下使用带 GRIN 透镜的光纤束探头提高尖端定时精度

叶片尖端计时 (BTT) 方法已成为叶片振动测量的行业标准。它根据叶片振动和非振动之间的不同到达时间 (ToAs) 监测叶片振动。光纤束 (OFB) 探针因其体积小、响应快和尖端定时精度高而被广泛用于获取 ToA。ToA 通常是通过将接收到的信号与固定的阈值电平进行比较来获得的。然而,叶片叶尖间隙(BTC)的变化会影响接收到的信号,直接导致叶尖定时误差。我们提出了一种带有 GRIN 透镜的光纤探头,它通过恒定分数鉴别 (CFD) 方法消除了由改变 BTC 引起的尖端定时误差。首先建立了带GRIN透镜的OFB探头模型。模型分析表明,无论BTC如何变化,所提出的方法获得的ToA都是恒定的。最后通过两个实验验证了模型的准确性和方法的有效性。当 BTC 从 1.5 到 3.5 mm 变化时,没有和有 GRIN 透镜的 OFB 探头的最大尖端定时误差分别为 181.12 μs 和 10.44 μs。
更新日期:2021-11-18
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