Computation of 2D Stokes flows via lightning and AAA rational approximation

Low Reynolds number fluid flows are governed by the Stokes equations. In two dimensions, Stokes flows can be described by two analytic functions, known as Goursat functions. Brubeck and Trefethen (2022) recently introduced a lightning Stokes solver that uses rational functions to approximate the Goursat functions in polygonal domains. In this paper, we present a solver for computing 2D Stokes flows in domains with smooth boundaries and multiply-connected domains using lightning and AAA rational approximation (Nakatsukasa et al., 2018). This leads to a new rational approximation algorithm "LARS" that is suitable for computing many bounded 2D Stokes flow problems. After validating our solver against known analytical solutions, we solve a variety of 2D Stokes flow problems with physical and engineering applications. The computations take less than a second and give solutions with at least 6-digit accuracy.