Characterizing Dry Ice Particle Response for Clean SeedingPIV Applications

摘要

Particle imaging velocimetry has been carried out in supersonic flow fields by seeding the plenum with carbon dioxide expanded from a high pressure tank through an orifice surrounded by a shroud tube. The experiment was successfully applied in two different supersonic wind tunnel facilities of different scale. For both tunnels, seeding density was sufficient for boundary layer thickness measurements. In the smaller tunnel, with a 6.3 cm by 6.3 cm cross section, mean velocity measurements leading to a characterization of particle response were carried out for Mach 3 flow over a 10-degreee ramp. The particle lag across the shock wave was quantified, and the results suggest that the particle size in the test section was consistent with particle diameters between 1 μm and 2 μm. In general, the mean velocity pattern compares favorably with expectations. Boundary layer thickness was also measured upstream of the ramp for two different stagnation pressure conditions, and the Reynolds number effect was in good agreement with theory. Boundary layer thickness and freestream velocities were also measured for the larger tunnel, which has a 15.2 cm by 15.2 cm cross section. An effort to reduce particle lag by injecting a co-flow of air within the shroud tube of the injector is documented. While the addition of co-flow did produce smaller particles exiting the shroud tube, as measured using a Malvern Spraytec particle size analyzer, the particle density achieved during the tunnel testing dropped to the point that condensate, rather than discrete particles, dominated the test section.