Point Doppler velocimetry measurements in circular jets

Improvements have been made to an existing 2-component Point Doppler Velocimetry (PDV) system to improve instrument accuracy and repeatability and to reduce mean velocity offset. Most importantly, the original iodine cells have been replaced by vapor-limited iodine cells that are not influenced by room temperature variations. PDV is a non-intrusive laser based flow measurement technique with capabilities that are similar to hot wire anemometry, but without inserting a probe into the flow. The insertion of a probe into a flow can affect the flow, resulting in inaccurate measurements.;PDV measurements for 1 inch diameter standard, swirling, and annular jets have been made at a nominal exit velocity of 60 m/s, corresponding to a Reynolds number of 100,000. Measurements of radial profiles of mean and RMS velocities were taken for each jet from the jet exit to X/D=12 at nine different X locations. Also, centerline velocity profiles were taken from the jet exit to X/D=12. Comparisons between hot wire anemometry and PDV measurements have been made for standard and swirling jets, and PDV data repeatability has been judged by multiple runs for each jet.;Hot wire anemometry measurements in the swirling jet appear to be inaccurate for X/D ≤ 4 due to the inability of the hot wire anemometer to accurately measure two-dimensional flow velocities. The PDV and hot wire comparisons for the standard jet have good correlation for the mean velocity; however, the RMS velocities do not agree. PDV measurements of the axial and circumferential mean velocities exhibited an uncertainty and repeatability of 2 m/s. This error, for the axial mean velocity, was of the same order as was produced by using a different calibration from the same day. PDV RMS velocities exhibited a repeatability of 0.5--1.0 m/s, and generally are about one half as large as the hot wire anemometer RMS velocities