Remarques sur l'instabilité du problème des poches de tourbillon. (Remarks on the instability of the vortex patch problem)
The author considers the two-dimensional Euler equation with an initial vortex being the characteristic function of some domain, given by a boundary T. The main result is an instability in finite time of this boundary T (which is considered closed to a unit circle). Perturbation equations are of second order. The method is related with the paper of \textit{P. Constantin} and \textit{E. S. Titi} [Commun. Math. Phys. 119, No.2, 177-198 (1988; Zbl 0673.76025)].
scientific article; zbMATH DE number 4210685