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 (, tip speed) are reported. At these speeds the measured uncertainty of the tip position was less than , 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.
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