Characterization and Control of Carbon Dioxide Seed Particle Image Velocimetry

Particle Image Velocimetry (PIV) data was acquired in two separate supersonic wind tunnels with carbon dioxide (CO2) particles utilized as the seed material. Previous work in clean seeding showed CO2 could be used as seed material to produce velocity maps. This research provides the first quantitative assessment of particle response, particle size control via purge gas, and scalability using CO2 particles. A variety of feed tube and shroud configurations, in combination with varying volumetric flow rates of purge air were measured using a laser diffraction device. The CO2 particles were injected into the stilling chamber of two open-circuit blow down supersonic wind tunnels to obtain PIV measurements. Results from each tunnel produced accurate free stream velocity measurements and demonstrate the ability to perform a basic boundary layer analysis. A ten degree ramp placed in the test section of the smaller wind tunnel produced a shock wave which allowed for the characterization of the time response of the CO2 particles as they crossed the shock wave. This time response was compared with theoretical time responses of varying diameter CO2 particles in order to characterize the spherical diameter of the actual CO2 particles in the test section. Purge air fed into the shroud tube was used to demonstrate the ability to alter the size of particles. A scale up was performed to demonstrate the applicability of the clean seeding technique to different size wind tunnels. Initial particle measurements demonstrate the ability to control the size of CO2 particles