Flexible endoscopic PIV and its application in velocity field measurement of confined spaces
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摘要:
面向航空发动机压气机/风扇内部狭小空间的内窥粒子图像测速（PIV）测量挑战，提出了柔性内窥PIV方法。基于测试环境约束条件，自主研制了适用于狭小空间探测的内窥成像镜头，并将其与光纤传像束及跨帧相机集成，构建了流场内窥采集系统。通过标定实验量化了引入光纤束导致的光学损耗与非均匀性，并提出了逐像素补偿方法以显著提升柔性内窥系统的图像质量。实验验证表明：该柔性内窥PIV系统成功获取了预期的湍流射流速度分布。与传统PIV测量结果对比，其平均相对误差控制在3%以内，验证了系统的准确性。方法有效克服了传统刚性内窥镜在振动环境中视野受限、易产生运动模糊及安装可靠性不足的局限性，为航空发动机内部复杂流场的精细化测量提供了一种技术途径。
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关键词:
- 航空发动机内流场 /
- 粒子图像测速（PIV） /
- 内窥粒子图像测速（PIV） /
- 柔性光纤传像 /
- 光学标定
Abstract:Facing the challenge of endoscopic particle image velocimetry (PIV) measurements within the confined spaces of aero-engine compressors and fans, a flexible endoscopic PIV method was proposed. This approach employed a flexible fiber-optic image bundle as the core image transmission component, and integrated with a self-developed endoscopic lens. It effectively overcame the limitations of traditional rigid endoscopes in vibration-prone environments, such as restricted field of view, susceptibility to motion blur, and insufficient installation reliability. Based on the test constraints of the internal flow field in a certain type of aero-engine compressor, a self-developed endoscopic imaging lens suitable for confined space detection was designed. This lens was integrated with a fiber-optic image bundle and an interframe camera to construct an endoscopic flow field acquisition system. Calibration experiments were conducted to quantify the optical loss and optical non-uniformity introduced by the fiber bundle. A pixel-by-pixel compensation method was proposed to significantly enhance the image quality of the flexible endoscopic system. Experimental validation demonstrated that this flexible endoscopic PIV system successfully captured the intended turbulent jet velocity distribution. Compared with traditional PIV measurements, the results presented an average relative error controlled within 3%, effectively verifying the system's accuracy. This method could provide a technical approach for refined measurements of complex flow fields within aero-engines.
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图 2 某型航空发动机风扇/压气机内流场的测试约束条件
Figure 2. Test constraints for the internal flow field of a certain type of aircraft engine fan/compressor
图 5 光纤内窥镜标定系统示意图
Figure 5. Schematic diagram of the fiber-optic endoscope calibration system
图 7 光纤束耦合/非耦合模式下的非线性度对比
Figure 7. Comparison of nonlinearity with and without fiber bundle coupling
图 9 光纤束耦合/非耦合模式下的非均匀度对比
Figure 9. Comparison of non-uniformity with and without fiber bundle coupling
图 11 光纤束耦合/非耦合模式下的特征线宽灰度值对比
Figure 11. Gray value comparison of characteristic line width measurements with and without fiber bundle coupling
图 13 工况2粒子图像与速度分布
Figure 13. Particle images and instantaneous velocity distributions for case 2
图 14 两种工况下瞬时/时均速度场分布
Figure 14. Instantaneous and time-averaged velocity distributions under two operating conditions
图 15 传统PIV与柔性内窥PIV测速结果对比
Figure 15. Comparison of measured velocity by conventional PIV and flexible endoscopic PIV
表 1 振动量图像质量衡量指标（振动频率为60 Hz，加速度为3.52g）
Table 1. Vibration image quality measurement index under vibration （frequency of 60 Hz and acceleration of 3.52g）
参数 帧数 相对
偏差/%第1帧 第2帧 平均灰度
梯度0.1485 0.1445 2.6700 灰度标准差 0.2322 0.2268 2.3200 模糊度 1.0000 0.9733 2.6680 
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表 2 振动量图像质量衡量指标（振动频率为150 Hz，加速度为22.18g）
Table 2. Vibration image quality measurement index under vibration （frequency of 150 Hz and acceleration of 22.18g）
参数 帧数 相对
偏差/%第1帧 第2帧 平均灰度
梯度0.1471 0.1478 0.4900 灰度标准差 0.2263 0.2277 0.6300 模糊度 0.9952 1.0000 0.4870
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