Re-entrant jet mechanism for periodic cavitation shedding in a cylindrical orifice

Periodic shedding of cloud cavitation is a common form of cavitation instability. The motion of a re-entrant liquid jet is central to this process but the mechanism which drives the phenomenon remains unclear, particularly for cavitation in cylindrical orifices. The current work describes an experimental investigation of the re-entrant jet mechanism for periodic cloud shedding in a large-scale (8.25 mm) cylindrical acrylic orifice. Refractive index matching and high-speed visualisation reveal in detail the motion of the re-entrant jet and indicate a complex mechanism causing the instability. Unabated optical access to the near-wall region of the orifice revealed a constant presence of liquid throughout the shedding cycle. The mechanism causing the periodic shedding was shown to be a combination of a traveling wave style deformation of the cavity interface and a translational pulse, each with distinctly different velocities.