  We study the dynamics of a dilute solution of rigid rodlike polymers in a
viscous fluid at low Reynolds number by means of numerical simulations of a
simple rheological model. We show that the rotational dynamics of polymers
destabilizes the laminar flow and causes the emergence of a turbulent-like
chaotic flow with a wide range of active scales. This regime displays an
increased flow resistance, corresponding to a reduced mean flow at fixed
external forcing, as well as an increased mixing efficiency. The latter effect
is quantified by measuring the decay of the variance of a scalar field
transported by the flow. By comparing the results of numerical simulations of
the model in two- and three-dimensions, we show that the phenomena observed are
qualitatively independent on the dimensionality of the space.
