| The tiny tip clearance between the inner wall of the aeroengine case and the tip of the rotating blade is an important parameter affecting the efficiency and performance of the aeroengine.The on-line measurement of blade tip clearance is very important for the safety working,design and even blade tip clearance control of aeroengine.There are the massive data processing problems caused by high-speed sampling,and the application requirements of high-precision blade tip clearance on-line measurement under the condition of low-speed sampling.According to the principle of capacitive blade tip clearance measurement,this paper puts forward a method of blade tip clearance measurement signal processing based on root mean square analysis of tip clearance measurement signal,and develops a dynamic blade tip clearance calibration method matching with this method,and completes the construction and experimental verification of the prototype of blade tip clearance online measurement system.The main contents of this paper are as follows:1.This paper analyzes the working principle of capacitance sensor and the requirement of measuring blade tip clearance of aeroengine,constructs the measurement model of blade tip clearance,and explores the law of the measurement of the blade tip gap measurement signal,which lays the foundation for the research of the signal processing method of the blade tip gap measurement.2.A signal processing method of blade tip clearance measurement based on RMS analysis is proposed.The corresponding relationship between the RMS value of real-time signal waveform and single tip clearance and the overall tip clearance of rotor has been constructed.The RMS value of blade tip clearance measurement signal is calculated in real time by analog circuit to realize the conversion from high-frequency tip clearance measurement signal to low-frequency RMS value signal.This paper analyzed main factors which affect the RMS value of the signal,and clarified the optimal method by simulation for measurement.The results proved that this method can reduce the amount of signal data and the amount of system calculation compared to traditional signal processing methods for blade tip gap measurement.3.A dynamic tip clearance calibration method matching with the RMS value processing of tip clearance measurement signal is developed,which is different from the traditional static calibration.A rotating blade calibration platform is built by using displacement platform and grating ruler,and the moving distance of displacement platform is read in real time during the blade rotation process to realize the dynamic calibration of tip clearance measurement results.The polynomial fitting calibration model of the measurement system is constructed,and the calibration data are analyzed.The fitting residual of the calibration model under different order conditions is compared,and the accurate calibration of the relationship between the gap signal RMS value and the theoretical gap value is achieved.4.In this paper,a capacitive blade tip gap online measurement system is built.Based on the project requirements,a circuit which realizes the calculation of analog signal RMS has been designed.Base on the Qt platform,this paper develops the host computer software which can realize the functions of parameter configuration,data display and storage.A high-speed rotating blade experiment platform was built,and experiments such as precision comparison and system performance testing were carried on.Meanwhile,this measurement system was successfully applied to the compressor testing platform.Within the measurement range of 0.3-3mm,the absolute error of the measurement system studied in this paper is within ± 25μm. |
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