Local dissipation scales in turbulent jets

This work characterizes the local dissipation length-scale η and its related quantities in turbulent (round and square) jets. It is revealed that the probability density function (PDF) of η, denoted by Q(η), displays different shapes in the jet's central region and shear layer. In the central jet of full turbulence, the distribution of Q(η) is insensitive to changes in the initial flow conditions and the degree of anisotropy, and agrees well with those obtained previously from a pipe flow and DNS of a box turbulence. On the other hand, the left tail of Q(η) at small η rises with increasing lateral distance from the centerline (toward the jet outer region), where the turbulent/non-turbulent intermittency occurs due to jet engulfment of ambient fluid; such large-scale intermittency is expected to enhance fine-scale dissipation intermittency. Therefore, the present work demonstrates that the smallest-scale dissipation fluctuations behave universally as in fully turbulent flows, irrespective of the flow type; but this universality is broken in partially turbulent flows or in flow regions where large-scale intermittency emerges.