Experiments with vortex rings in airR. H. Hernández, B. Cibert and C. Béchet
LEAF-NL, Departamento de Ingeniería Mecánica, Universidad de Chile Santiago, Chile
received 15 March 2006; accepted in final form 12 July 2006
published online 28 July 2006
We report quantitative experimental measurements of the instability of vortex rings generated in air. Vortex rings are created by pushing air through the circular orifice of a cylindrical cavity with a flat piston driven by a loudspeaker. Hot-wire anemometry provides accurate measurements of the velocity profile at all stages of the ring formation including stable and unstable rings. Flow visualization using a laser light sheet shows that the initially undisturbed vortex ring is progressively deformed in the azimuthal direction giving rise to a wavy azimuthal and periodic pattern in the circumference of the ring. The wavy pattern is steady, i.e., it does not rotate or translate during the ring's motion. However as the vortex motion progresses in the axial direction, the displaced portions of the ring are convected away from the initial undisturbed position and the wavy pattern grows with local Reynolds number.
47.15.-x - Laminar flows.
47.20.-k - Flow instabilities.
© EDP Sciences 2006