Localized measurement of the velocity of flow In fluids may be accomplished by detecting the Doppler shift In frequency from coherent, monochromatic light scattered from micrometer sized contaminant particles within the flow. The versatility of applications of this technique, first used several years ago, has been expanded by recent research. The basic geometry of measurement, in which the scattered energy is recombined with light energy at the original frequency on the face of the photocathode of a photomultiplier tube, can be rearranged in many alternative configurations to meet the needs of the experimenter. By using a single laser, additional arrangements are possible for obtaining two- or three-dimensional measurements of velocity components. Several different velocimeters are described for making two-dimensional flow measurements, including both backscatter and forward scatter systems. Effects of flow system geometries on capabilities for measuring specific components are investigated. Effects of laser beam polarization are discussed and conclusions reached on methods of optimizing signal strength in each of two orthogonal measurement systems. Results of the application of a two-dimensional measurement system used for obtaining velocity profiles in turbulent flow in a smooth walled four-inch diameter pipe are presented. Operating at a Reynolds number of about 1.1 x 106, relative turbulent intensities were measured in the axial direction and normal to that direction. Standard techniques were utilized. A second readout system was employed to make a measurement of this parameter without the requirement of adding scattering centers to the flow
