Instability of a columnar vortex in a stratified fluid

B. Cariteau , Jan-Bert Flór (1)

1 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

We experimentally investigate the stability of a monopolar columnar vortex in a linearly stratified fluid. The vortex was generated by a single flap of which the rotation about the vertical axis was accelerated and subsequently decelerated, resulting in an approximately Gaussian vorticity profile. The Reynolds number Re=UR/n was of order O(1000), with U the maximum azimuthal velocity and R the corresponding radius, while the Froude number Fr=U/(RN), with N the buoyancy frequency, ranged between 0.5 and 5. Though these vortices are centrifugally and elliptically stable for Fr<2, they are unstable due to a resonant interaction between inertial and gravitational oscillations that occur near the radius where the angular velocity approaches N. This instability is apparent as a helical wave, of which the wavelength varies monotonically with F. To our knowledge this instability has not been observed before, and differs from the so-called zigzag instability observed by Billant and Chomaz (2000).

Mots clés: Instability stratified fluids

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

B. Cariteau, Jan-Bert Flór. Instability of a columnar vortex in a stratified fluid. APS Division of Fluid Dynamics 56, Aug 2003, East Rutherford, United States. ⟨hal-00206312⟩