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International Symposium on Heat Transfer in Turbomachinery
August, 24-28, 1992 , Marathon, Greece

DOI: 10.1615/ICHMT.1994.IntSympHetatTransTurb


ISBN Print: 1-56700-016-9

ISBN Print: 978-1-56700-016-0

A Miniature Laser Diode Based Laser Doppler Anemometer for Turbomachinery Flow Measurements

pages 125-130
DOI: 10.1615/ICHMT.1994.IntSympHetatTransTurb.100
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With the recent advancements in solid state lasers and solid state avalanche photodiodes, it is possible to construct miniature Laser Doppler Anemometers (LDA) employing entirely solid state technology. Such systems have the advantages of small size, light weight, extreme ruggedness, and minimal power consumption. It is expected that solid state LDA systems will enable direct LDA measurements of turbomachinery rotor flows by rotating them in the rotor frame of reference. All connections to such a solid state LDA system could be made with mercury slip ring units. The subject of the current research was to evaluate a visible laser diode's abilities and limitations in a miniaturized LDA system. Future research will entail an extension of the current one-component system to two components with directional discrimination.
A basic one dimensional LDA was designed, constructed, and thoroughly evaluated employing a 10 milliwatt visible (670 am) index guided laser diode. The design problems specifically associated with the use of a laser diode are discussed, and their solutions presented. The probe volume shape unique to laser diode LDA systems is also presented. The miniature LDA system was used to measure mean and RMS turbulent velocities in a low speed impinging jet, and the results were compared to data obtained by both hot-wire and five-hole probes. A thorough uncertainty analysis was performed on the measurements in an effort to evaluate the ability of the LDA system to measure both mean and turbulent flow velocities.
Overall, the miniature LDA system with the visible laser diode was found to be capable of accurate measurements, and it appears to hold promise in enabling LDA measurements in difficult to measure turbomachinery flow situations. Mean velocities in the jet were found to be accurate to within 2%, and RMS turbulent velocities were found to be accurate within roughly 5-20%. An additional correction to the miniature LDA system involving the intensity distribution of the laser diode beam in the crossing plane is expected to improve the accuracy even further.

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