DESIGN CONSIDERATIONS FOR A 3-DIMENSIONAL FIBER-OPTIC LASER-DOPPLER-VELOCIMETER FOR TURBOMACHINERY APPLICATIONS

Single headed three dimensional (3D) laser Doppler velocimetry (LDV) g eometries generally rely upon the use of three Doppler difference chan nels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measuremen t coordinate system and the Cartesian system can result in large error s in the calculated velocities. A theoretical analysis of the geometri cally induced uncertainties in measurements produced by four single he aded 3D LDV configurations is presented. These considerations have lea d to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measu re the on axis velocity component. The f/4 probe head has a working di stance of 200 mm, designed to operate within the constraints of the li mited optical access available in turbomachinery applications. (C) 199 7 American Institute of Physics.