Turbine blade tip clearance measurement using a skewed dual-beam fiber optic sensor

Optimization and active control of the tip clearance of turbine blades has been identified as a key to improve fuel efficiency, reduce emission, and increase service life of the engine. However, reliable and real-time tip clearance measurement is difficult due to the adverse environmental conditions that are typically found in a turbine. We describe a dual-beam fiber optic measurement system that can measure the tip timing and tip clearance simultaneously. Because the tip timing information is used to calculate the tip clearance, the method is insensitive to the signal intensity variation caused by fluctuations in environmental conditions such as light source instability, contamination, and blade tip imperfection. The system was calibrated and tested using experimental rotors. The test results indicated a high resolution of 4.5 mu m and measurement accuracy of +/- 20 mu m over the rotation speed range of 2000 to 10,000 rpm. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.8.081514]