Validating advection-corrected correlation image velocimetry*

We investigate the formation and subsequent shock acceleration of a gravity-driven curtain of massive particles, where the initial particle volume fraction in the curtain can vary between 1 and 10%. The process of the curtain formation and evolution is recorded in two imaging planes (planar and side views). The high seeding density of the particles in the curtain presents a challenge for visualization and analysis using laser-sheet techniques such as particle image velocimetry. Instead of laser sheets, we have to rely on diffuse constant-intensity light for visualization. The resulting images allow us to apply several techniques: particle-image velocimetry (with a caveat that the plane of visualization is defined not by the lighting, but by the flow geometry and the camera depth of focus), particle tracking, and image-correlation velocimetry with advection correction. Comparison between the results also presents us with an excellent opportunity to cross-validate the diagnostics.