We have performed simulations of hairpin vortex evolution in a channel flow in which a passive scalar was present. The hairpin was created by disturbing the flow using an impulsive and spatially localized body force. Simultaneous with the introduction of the force, a passive scalar was introduced. The simulations were performed using a spectral code at a Reynolds numbers of 3000. The results show that a significant fraction of the scalar material is spontaneously trapped in the core of a hairpin vortex. This can be understood by recalling that vortex lines are material lines in flows for which the effects of diffusion are small. We will also discuss the possible implications of these observations with respect to the introduction of active scalars coincident with regions of concentrated vorticity.
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