Weak vorticity formulation for the incompressible Euler equations in domains with boundary

Dragos Iftimie (1) , Milton Lopes Filho (2) , Helena Nussenzveig Lopes (2) , Franck Sueur (3)

1 ICJ - Institut Camille Jordan
2 IM / UFRJ - Instituto de Matemática da Universidade Federal do Rio de Janeiro
3 LJLL - Laboratoire Jacques-Louis Lions

In this article we examine the interaction of incompressible 2D flows with compact material boundaries. Our focus is the dynamic behavior of the circulation of velocity around boundary components and the possible exchange between flow vorticity and boundary circulation in flows with vortex sheet initial data. We formulate our results for flows outside a finite number of smooth obstacles. Our point of departure is the observation that ideal flows with vortex sheet regularity have well-defined circulations around connected components of the boundary. In addition, we show that the velocity can be uniquely reconstructed from the vorticity and boundary component circulations, which allows to recast 2D Euler evolution using vorticity and the circulations as dynamic variables. The weak form of this vortex dynamics formulation of the equations is called the {\em weak vorticity formulation}. Our first result is existence of a solution for the weak velocity formulation with vortex sheet initial data for flow outside a finite number of smooth obstacles. The proof is a straightforward adaptation of Delort's original existence result and requires the usual sign condition. The main result in this article is the equivalence between the weak velocity and weak vorticity formulations, without sign assumptions. Next, we focus on weak solutions obtained by mollifying initial data and passing to the limit, with the portion of vorticity singular with respect to the Lebesgue measure assumed to be nonnegative. For these solutions we prove that the circulations around each boundary component cannot be smaller than the initial data circulation, so that nonnegative vorticity may be absorbed by the boundary, but not produced by the boundary. In addition, we prove that if the weak solution conserves circulation at the boundary components it is a {\it boundary coupled weak solution}, a stronger version of the weak vorticity formulation. We prove existence of a weak solution which conserves circulation at the boundary components if the initial vorticity is integrable, i.e. if the singular part vanishes. In addition, we discuss the definition of the mechanical force which the flow exerts on material boundary components and its relation with conservation of circulation. Finally, we describe the corresponding results for a bounded domain with holes, and the adaptations required in the proofs.

Domaines: Equations aux dérivées partielles [math.AP]

Dragos Iftimie, Milton Lopes Filho, Helena Nussenzveig Lopes, Franck Sueur. Weak vorticity formulation for the incompressible Euler equations in domains with boundary. 2013. ⟨hal-00820998⟩