Demonstration of Clean Particle Seeding for Particle Image Velocimetry in a Closed Circuit Supersonic Wind Tunnel

摘要

The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV) for use in a closed circuit supersonic wind tunnel. The Air Force Institute of Technology (AFIT) closed circuit pressure-vacuum supersonic wind tunnel was utilized, which achieves a nominal Mach number of Mach 2.9 in a 2.5 inch by 2.5 inch square test section. CO2 was dispensed into the flow as a liquid from a standard compressed gas liquid tank through two different injector styles at two injection sites using various injector attitudes. Upon exiting the injector in either the stagnation chamber or converging-diverging nozzle, the liquid CO2 rapidly formed solid particles which became entrained in the wind tunnel flow and began the sublimation process from a solid to a gaseous state. The particles traveled through the test section, in which they were illuminated by a laser, and the light scattered by the particles was imaged with a camera. The resulting images were processed using the Dantec Dynamics FlowManager PIV processing software to generate vector maps representing the flow field in the test section. The particles fully sublimated after traveling through the test section, making the injection process self cleaning and hazard free. Vector maps that matched the nominal 606 m/s velocity in the empty test section were generated utilizing both multi-port tube and shroud tube style injectors. Realistic vector maps were also generated for the flow with a 10. half-angle cone model placed inside the test section. Overall this research successfully demonstrated the use of CO2 as a seed material for PIV processing.