Optical Probe for Monitoring Blade Tip Clearance

The reduction of blade tip clearance in high pressure turbine (HPT) and high pressure compressor (HPC) engines, defined as the void between a blade tip and the surrounding casing, has been a subject of intense research since the inception of the gas turbine engine. A prototype sensor based on an interferometric ranging technique, was built and tested for monitoring tip clearances. The method provided measurement accuracy of better than 10 micrometers. It is robust, inherently self-calibrating, and insensitive to environmental variations. The performance of the sensor was evaluated in both room temperature and inside a tube furnace to simulate the turbine environment. The spatial resolution, clearance measurement accuracy, clearance measurement range, and sensitivity of the prototype sensor were determined. The sensor system will provide a new tool for engine manufacturers to study and optimize blade tip clearance with high accuracy without the need for repetitive and cumbersome calibration procedures.