A comparison of measurements of mean velocity and turbulence intensity in an unheated, subsonic, free-jet airflow made concurrently with a laser Doppler velocimeter and a hot-wire anemometer

A single-component, Bragg-diffracted laser Doppler velocimeter was used to measure the mean velocity and turbulence intensity in an unheated, subsonic, free-jet airflow. The results were compared to measurements taken concurrently with a hot-wire anemometer at axial positions 1, 2, 4, and 8 nozzle diameters downstream of the nozzle exit plane. Favorable agreement was obtained for the mean velocity results at all but one axial station. Significant anomalies were noted in the LDV results for turbulence intensity when compared to the hot-wire results. Several possible sources for the discrepancies were identified including broad confidence intervals in the LDV data due to the small sample size, LDV probe volume and hotwire probe misalignment, differences in the components of velocity sensed by the two probes, low frequency oscillations in the airflow due to control problems, and LDV signal processor parameter selection.