Total velocity vector measurements in an axial-flow compressor using a 3-component Laser Doppler Anenometer

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Virginia Tech


A three-color, three-component Laser Doppler Anemometer (LOA) capable of making simultaneous measurements of three components of velocity is described, and the use of this LOA to measure three non-orthogonal velocity components in the rotor blade passage of a single-stage axial-flow compressor is reported. Measurements were made at four radial locations from 50% span out to the blade tip, and at seven different axial locations from -0.55 axial chord 1.40 axial chord. Measurements were made at only one throttle setting.

The measured velocities are used to determine the flow in the orthogonal axial - tangential - radial, x - t - r, coordinate system of the compressor. Although the mean velocities and entire Reynolds stress tensor are obtained with this system, only the mean velocities are reported. Results are presented in the form of a series of vector plots showing: 1.) the primary flow as projected on the x - t plane and 2.) the secondary flow in the t - r plane. The LOA measurements are shown to agree with pitot probe measurements in the stationary frame and basic secondary flow theory.

A detailed error analysis is presented, taking into account both measurement uncertainties and statistical biasing. An analysis is also made of particle lag in the rotating flow of the compressor blade passage.

A discussion of the difficulties encountered in making three dimensional velocity measurements in turbomachinery blade passages is presented. Suggestions are made for improving the present system for this task.