A laser Doppler based method for in situ single blade tip clearance measurements of turbomachines with high precision is presented for what we believe is the first time. The sensor is based on two superposed fanlike interference fringe systems generated by two laser wavelengths from a fiber-coupled, passive, and therefore compact measurement head employing diffractive optics. Tip clearance measurements at a transonic centrifugal compressor performed during operation at 50,000 rpm (833 Hz, 586 m/s tip speed) are reported. At these speeds the measured uncertainty of the tip position was less than 20 μm, a factor of 2 more accurate than that of capacitive probes. The sensor offers great potential for in situ and online high-precision tip clearance measurements of metallic and nonmetallic turbine blades.
© 2006 Optical Society of America
Instrumentation, Measurement, and Metrology
Original Manuscript: December 14, 2005
Revised Manuscript: January 23, 2006
Manuscript Accepted: January 24, 2006
Lars Büttner, Thorsten Pfister, and Jürgen Czarske, "Fiber-optic laser Doppler turbine tip clearance probe," Opt. Lett. 31, 1217-1219 (2006)