A dynamic turbine tip clearance measurement method based on laser self-mixing interferometric ranging considering Doppler effect

Abstract

Abstract In view of the Doppler effect caused by rotating blades during dynamic measurement, which reduces the accuracy of tip clearance measurement, a dynamic measurement method of turbine tip clearance based on laser self-mixing interferometric ranging considering the Doppler effect is proposed. Firstly, a self-mixing interference model based on the three-mirror Fabry–Pérot cavity model is proposed. Then, the relationship between distance, frequency, and rotational speed is constructed which lays the foundation for the dynamic measurement of the blade tip clearance. What’s more, the composition of the dynamic self-mixing interferometry system including each experimental measurement parameter is described. Finally, the experimental validation is performed to investigate the relationship between the actual measured distance and frequency after compensating for Doppler shift as well as the accuracy of blade tip clearance measurement. Experimental results demonstrate that as the rotational speed gets faster, greater Doppler frequency shift is generated. Meanwhile, the effect on the accuracy of measurement of blade tip clearance is more obvious. The method considering the influence of Doppler effect effectively improves the reliability and accuracy of the dynamic measurement system of blade tip clearance. The standard deviation of dynamic measurement of blade tip clearance can reach up to 13 μm.