Measurement and Image Processing Techniques for Particle Image Velocimetry Using Solid-Phase Carbon Dioxide

Proper seeding material for particle image velocimetry (PIV) should not contaminate closed circuit wind tunnels and minimize residual deposits on walls. Solid carbon dioxide (dry ice) particles are ideally suited to meet this requirement. However, to obtain accurate velocity measurements, either particle size must be controlled or advanced image filtering and processing must be implemented. Both of these approaches are explored and advanced in the following research. Refined data processing was conducted on previously collected turbulent boundary layer PIV data utilizing a similar particle generation system. The re-processed data trended more closely with corresponding pitot probe data than the original results. Free stream velocity measurements were within 0.97% of wind tunnel data free stream calculations. Particle sizing measurements of solid-phase carbon dioxide (CO2) were demonstrated in bench test experiments using an image-based approach. Dry air and gaseous CO2 were introduced into a specific CO2 injector in an attempt to control particle diameter, for diameters that ranged from 20 m to 2800 m. Average particle diameter was represented by an area-equivalent diameter and Sauter mean diameter. The greatest reduction in particle diameter was measured using dry air in conjunction with the CO2 injector, where a 21% decrease in average area-equivalent diameter was observed. In contrast, there was only about an 8% decrease in the average area-equivalent diameter with gaseous CO2. Dry air was introduced into the same CO2 injector for particle sizing experiments in the test section of an Air Force Institute of Technology (AFIT) Educational Wind Tunnel (EWT). Shadow images were taken at the inlet section of the EWT and at the test section for a comparison of the particle size distribution at each location. Changes in particle size with free stream velocity and increased mass flow rates of air were observed