L. Moriconi, R. M. Pereira
Time scales of turbulent strain activity, denoted as the strain persistence times of first and second order, are obtained from postulated similarity laws for the expectation values and correlation functions of lagrangian rate-of-strain eigenvalues in particularly defined statistical ensembles. We discuss, within a gaussian closure approximation for single-point vorticity statistics, a simple and computationally efficient method for the evaluation of the strain persistence times, which copes well with direct numerical simulation data. At asymptotically large strain, it turns out that while the strain persistence time of first order can be identified with the usual "1/s" estimate of standard turbulence phenomenology, the strain persistence time of second order contains a divergent logarithmic prefactor which is suggestively related to the emergence of small-scale coherent structures.
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http://arxiv.org/abs/1204.5150
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