Instabilities and mixing in two-dimensional Kolmogorov flow

This paper presents results of a theoretical investigation of transport in a numerical model of a two-dimensional Kolmogorov flow. We investigate the changes in its mixing properties associated with transition from laminar regime to turbulence. It is found that significant changes in the flow do not always lead to comparable changes in its transport properties. On the other hand, some very subtle changes in the flow can dramatically alter the degree of mixing. We show that interaction of multiple resonances can provide an explanation for many of these seemingly paradoxical results.