Clean Seeding for Particle Image Velocimetry

Particle Image Velocimetry (PIV) is a flow velocity measurement technique in which small seed particles are inserted into a flow and tracked through photography. Traditional PIV techniques utilize solid or liquid seed particles that can persist in closed circuit wind tunnels and corrode or damage components of the tunnel or model. Solid carbon dioxide (CO₂) is an alternative seed material that neither persists in closed loop wind tunnels nor damages any tunnel components. This research effort demonstrates the viability of CO₂ as a PIV seed material in a supersonic blow down tunnel. Experiments were conducted with an empty test section, a cavity flow and a cone model present in the test section. For the empty test section, the results compare to within 4% of the velocity predicted by one dimensional isentropic flow models. In addition, experiments were conducted for a cavity flow regime and for flow around a cone model. These additional experiments all qualitatively demonstrated expected flow characteristics.