Stationary Solutions to the Navier–Stokes System in an Exterior Plane Domain: 90 Years of Search, Mysteries and Insights

In this survey, we study the boundary value problem for the stationary Navier–Stokes system in planar exterior domains. With no-slip boundary condition and a prescribed constant limit velocity at infinity, this problem describes stationary Navier–Stokes flows around cylindrical obstacles. Leray’s invading domains method is presented as a starting point. Then we discuss the boundedness and convergence of general D-solutions (solutions with finite Dirichlet integrals) in exterior domains. For the Leray solutions of the flow around an obstacle problem, we study the nontriviality, and the justification of the limit velocity at small Reynolds numbers. Further, under the same assumption of small Reynolds numbers the global uniqueness theorem for the problem is established in the class of D-solutions, its proof deals with the accurate perturbative analysis based on the linear Oseen system, inspired by classical Finn-Smith technique; the classical Amick and Gilbarg–Weinberger papers are involved here as well. The forced Navier–Stokes system in the whole plane is also presented as a closely related problem. A list of unsolved problems is given at the end of the paper.