The existence of weak solutions to the "viscous incompressible fluid + rigid body" system with Navier slipwith-friction conditions in a 3D bounded domain has been recently proved by .In 2D for a fluid alone (without any rigid body) it is well-known since Leray that weak solutions are unique, continuous in time with L 2 regularity in space and satisfy the energy equality. In this paper we prove that these properties also hold for the 2D "viscous incompressible fluid + rigid body" system.

A classical model for sources and sinks in a two-dimensional perfect incompressible fluid occupying a bounded domain dates back to Yudovich's paper [44] in 1966. In this model, on the one hand, the normal component of the fluid velocity is prescribed on the boundary and is nonzero on an open subset of the boundary, corresponding either to sources (where the flow is incoming) or to sinks (where the flow is outgoing). On the other hand the vorticity of the fluid which is entering into the domain from the sources is prescribed.In this paper we investigate the existence of weak solutions to this system by relying on a priori bounds of the vorticity, which satisfies a transport equation associated with the fluid velocity vector field. Our results cover the case where the vorticity has a L p integrability in space, with p in [1, +∞], and prove the existence of solutions obtained by compactness methods from viscous approximations. More precisely we prove the existence of solutions which satisfy the vorticity equation in the distributional sense in the case where p > 4 3 , in the renormalized sense in the case where p > 1, and in a symmetrized sense in the case where p = 1.

On the 2D "viscous incompressible fluid + rigid body" system with Navier conditions and unbounded energy Sur le mouvement d'un corps rigide dans un écoulement bidimensionel d'un fluide visqueux incompressible avec conditions au bord de Navier et énergie infinie