Research On Blade Tip Clearance Measurement Technology Based On Microwave Sensor

Blade tip clearance can influent the performance and safety of gas turbine engine,and on-line blade tip clearance measurement plays an important role in active tip clearance control,structural health monitoring and aircraft performance test.At present,microwave blade tip clearance measurement is becoming a hotspot all over the world due to its adaptability in engines.In this paper,a series of analysis and experiments are carried out around the microwave blade tip clearance measurement.Firstly,the principle of microwave ranging based on phase modulation was introduced and the feasibility of microwave sensor used in turbine machine was also analyzed.The measurement system similar to microwave interferometer and the process of ranging by demodulating the phase difference between transmitted and received signal were introduced.Secondly,aiming at the measurement errors in the existing microwave displacement/distance measurement system.,according to the characteristics of measuring system and operating environment,the transceiver's signal leakage,background echo superposition,I/Q channel amplitude-phase imbalance,signal attenuation and spatial filtering effect were analyzed.The output form of I/Q channels including bias DC,I/Q error,signal attenuation,defocus interference was summarized.The influence of those error factors on ranging can be seen through modeling.Then,aiming at the problem that the calibration parameters such as bias DC,I/Q errors and real wavelength are difficult to obtain accurately at the same time,a method based on equivalent IF analysis is proposed.For the problem of inaccurate extraction of parameters by equivalent IF analysis,a parameter combination optimization method based on genetic algorithm was proposed.A miniaturized 24 GHz CW radar based on MMIC technology was adopted in the experiment.And the results showed that the equivalent IF analysis method can extract calibration parameters effectively,and the linearity of ranging is improved by 68.53% after using the optimization method.Finally,ranging experiments are carried out and the pattern of defocusing error caused by spatial filtering effect was summarized.The calibration method under certain conditions can eliminate defocusing error and the results showed that the ranging resolution is better than 0.01 mm,the static ranging error is less than 0.03 mm,and the standard deviation of repeatability experiment is better than 0.02 mm.At last the dynamic tip clearance measurement experiment showed great consistency to that of static displacement experiments.