Journal of Fluid Mechanics

How vortices mix

a1 IRPHE, Université de Provence, Aix–Marseille 1, Technopôle de Château-Gombert, 49, rue Frédéric Joliot-Curie, 13384 Marseille Cedex 13, France


The advection of a passive scalar blob in the deformation field of an axisymmetric vortex is a simple mixing protocol for which the advection–diffusion problem is amenable to a near-exact description. The blob rolls up in a spiral which ultimately fades away in the diluting medium. The complete transient concentration field in the spiral is accessible from the Fourier equations in a properly chosen frame. The concentration histogram of the scalar wrapped in the spiral presents unexpected singular transient features and its long time properties are discussed in connection with real mixtures.

(Received July 14 2002)
(Revised October 29 2002)