On the density patch problem for the 2-D inhomogeneous Navier-Stokes equations

In this paper, we first construct a class of global strong solutions for the 2-D inhomogeneous Navier-Stokes equations under very general assumption that the initial density is only bounded and the initial velocity is in H¹(R²). With suitable assumptions on the initial density, which includes the case of density patch and vacuum bubbles, we prove that Lions' s weak solution is the same as the strong solution with the same initial data. In particular, this gives a complete resolution of the density patch problem proposed by Lions: { for the density patch data ρ₀=1D with a smooth bounded domain D², the regularity of D is preserved by the time evolution of Lions's weak solution.}