Design and modeling of three-dimensional tip-clearance optical probe based on two-circle reflective coaxial fiber bundle

Based on the characteristics of strains which lead to failures of turbine blades inside the aero-engine, a three-dimensional fiber-optic tip-clearance measuring method using two-circle reflective coaxial fiber bundles as three measuring units is presented. Firstly, mathematical model of each unit when there exists radial clearance together with inclination at axial and circumferential direction of the reflector is built, including compensation algorithm of overlapped area between receiving fiber and the incident light, and correction algorithm of average light intensity on surface of virtual image of receiving fiber. It shows that this model could restore the real three-dimensional output behavior of the bundle by means of comparison between simulation results with experimental results reported in previous study. Then, evaluation of two different layouts of the three measuring units through simulation is given, which offers a proper theoretical basis of the final three-dimensional tip-clearance optical probe design and manufacture.