Capacitive Gap Measurement System Applied Research In Turbomachinery

The blade tip clearance is a key factor of improving aero-engine performance and insuring safety flight. The design of the blade tip clearance should be demonstrated by measurement in testing. In this paper, application research is done on a frequency modulated (FM) capacitance technique based blade tip measurement system CAPLONG.Firstly, methods of blade tip measurement are analyzed and contrasted. The principle of capacitive blade tip measurement system is deeply studied. Secondly, a synchronous sampling system is designed to matching the CAPLONG system. Detailed design and analysis of sensors, the phonic wheel and synchronous signal processing are done. Thirdly, calibrate methods are studied, and a calibrate scheme is designed. The system is calibrated on a compressor blisk and a turbine blisk respectively. The calibrate coefficients of polynomial of degree 7 are gotten with the least squares method. Since the precision of measurement is affected by many factors in engineering application, the correcting methods and database are researched and established in a laboratory to revise the effects of probes withdraw value, the mounting angle of probes, the ground resistance, the speed, the high temperature gas and the axial wobble.Finally, this system is applied successfully in a high-pressure-compressor testing. The blade tip clearance is real-time monitored and recorded digitally. With the data, the variation of blade tip clearance is analyzed in detail. Theoretic analysis and compressor experimentations demonstrated that it is dependable to measure the blade tip clearance and feasible to supervise the safety of devices with the capacitive blade tip clearance measurement system.