Research On Rotating Blade Tip Clearance Noncontacting Measurement In The Aero-engine

Blade tip clearance is an important parameter that influences the performance of aero-engine. On-line and real time measurement system of rotating blade tip clearance in a gas turbine is essential to the safe and efficient operation of aero-engine.Based on analysis of research status at home and abroad, optical fiber measuring method and capacitive measuring method is developed and demonstrated. The first method is applied to compressor stage under the appropriate circumstance of low temperature.The latter one is suited to high-pressure stage of gas turbine with high temperature. One of our research objectives is to build up a mathematic model of optical fiber bundle sensor and to optimize its sensor configuration. The other is to explore the whole scheme of capacitive probe tip clearance measurement system. According to measured environment, which build up a solid foundation to develop a practical blade tip clearance measurement prototype.Innovation points are as followings. Three-dimensional mathematic model based on ray tracing theory is proposed and demonstrated, and four-furcated optical fiber bundle sensor with compensated capability is developed combined with arts and crafts. The whole scheme of capacitive probe tip clearance measurement system is developed and mixer method is employed to improve sensitivity of measurement system.The research work in this paper mainly includes the following several parts.(1) Three-dimensional mathematic model based on ray tracing theory is built up and applied to analyze receiving light characteristic and designation of optical fiber bundle sensor.(2) Four-furcated optical fiber bundle sensor is designed. It's independent of light source fluctuation, target surface reflectivity and optical fiber loss during transmitting light, but dependent of tip clearance and small inclined angle between tip plane and sensor plane. By means of static and dynamic stimulant experiment, it is proved to be reliable.(3) According to measured environment of high-pressure stage of gas turbine, capacitive sensor that can resist heat with long cable is designed and connected to LC oscillatory electric unit with high stability.(4) Large capacitance is introduced by long cable of capacitive sensor, which influences sensitivivity and precision of the sensor. Mixer circuitry is employed to enhance sensitivity of measurement system by increasing relative frequency offset of FM signal.(5) Demodulated system of FM signal based on PLL is developed. The working reliability of capacitive sensor and interface circuitry is demonstrated by means of static experiment.