Refinement and Verification of the Virginia Tech Doppler Global Velocimeter (DGV)

Abstract

Repairs and modifications were made to a flow velocity measurement system designed to measure a planar area of unsteady three component velocities in a single realization using a velocity measurement technique referred to as Doppler Global Velocimetry (DGV). Several hardware components in the system were modified and new hardware was added. Significant improvements were made to the procedures used in acquiring DGV data as well as the procedures used in reducing the acquired DGV data. Though hardware problems were encountered, successful iodine cell calibrations were acquired and attempts were made to acquire DGV velocity data from a calibration wheel and in the wake of a 6:1 prolate spheroid. These attempts were hampered by poor performance of the Nd:YAG laser and one of the digital cameras used in this research. While the magnitudes of the velocities acquired from the calibration wheel were noticeably higher than those calculated from the angular velocity and large fluctuations were present in these reduced velocities, the general trends measured by the VT DGV system matched those calculated from the angular velocity. The attempt to acquire flow field data in the wake of a 6:1 prolate spheroid model was unsuccessful due to insufficient seed particle density in the area where data were to be obtained. The results of this research indicate that while significant improvements have been made to the system, there are still some significant problems to overcome.