A Classification Theorem for Steady Euler Flows

Fix a bounded, analytic, and simply connected domain $Ω\subset\mathbb{R}^2.$ We show that all analytic steady states of the Euler equations with stream function $ψ$ are either radial or solve a semi-linear elliptic equation of the form $Δψ= F(ψ)$ with Dirichlet boundary conditions. In particular, if $Ω$ is not a ball, then there exists a one to one correspondence between analytic steady states of the Euler equations and analytic solutions of equations of the form $Δψ= F(ψ)$ with Dirichlet boundary conditions.