Mixing in internally stirred flows

We consider mixing in a viscous fluid by the periodic rotation and translation of a stirrer, the Reynolds number being low enough that the Stokes approximation is valid in the unsteady, two-dimensional flow. Portions of the boundary of the container may also move to contribute to the mixing. The shapes of the stirrer and the container are arbitrary. It is shown that the recently developed embedding method for eigenfunction expansions in arbitrary domains is well suited to analyse the mixing properties of such mixers. This application depends crucially on the accurate analytical description of the complex, unsteady field. After carefully validating the proposed method against the recent results found in the literature, examples are given of how the method could be used in practice. A special advantage of the suggested method is that it can be extended to handle three-dimensional mixing flows with virtually no change in the procedure shown here.