  We consider the enhanced mixing due to multiple cylinders organised in
schools moving synchronously in a potential flow. Here simple interactions
between cylinders are modelled by the method of image doublets. This is an
extension to Thiffeault \& Childress's work [\emph{Physics Letters A}
\textbf{374}, 3487 (2010)] where fluid particle displacements due to
non-interacting swimmers were analysed to produce an effective diffusivity that
may have a significant impact in ocean mixing. Our results show that schools of
two cylinders induce nonlinearly boosted diffusivity compared with the
non-interacting case for general configuration parameters, except when they
move along a straight line with small separation. We attribute this phenomenon
to two different physical mechanisms via which interacting cylinders cooperate
to generate long particle drifts depending on their formation. Finally, the
effective diffusivity of schools of three or more cylinders in various
configurations are also discussed.
