Lagrangian statistics for Navier–Stokes turbulence under Fourier-mode reduction: fractal and homogeneous decimations

M Buzzicotti, A Bhatnagar, L Biferale… - New Journal of …, 2016 - iopscience.iop.org
New Journal of Physics, 2016iopscience.iop.org
We study small-scale and high-frequency turbulent fluctuations in three-dimensional flows
under Fourier-mode reduction. The Navier–Stokes equations are evolved on a restricted set
of modes, obtained as a projection on a fractal or homogeneous Fourier set. We find a
strong sensitivity (reduction) of the high-frequency variability of the Lagrangian velocity
fluctuations on the degree of mode decimation, similarly to what is already reported for
Eulerian statistics. This is quantified by a tendency towards a quasi-Gaussian statistics, ie, to …
Abstract
We study small-scale and high-frequency turbulent fluctuations in three-dimensional flows under Fourier-mode reduction. The Navier–Stokes equations are evolved on a restricted set of modes, obtained as a projection on a fractal or homogeneous Fourier set. We find a strong sensitivity (reduction) of the high-frequency variability of the Lagrangian velocity fluctuations on the degree of mode decimation, similarly to what is already reported for Eulerian statistics. This is quantified by a tendency towards a quasi-Gaussian statistics, ie, to a reduction of intermittency, at all scales and frequencies. This can be attributed to a strong depletion of vortex filaments and of the vortex stretching mechanism. Nevertheless, we found that Eulerian and Lagrangian ensembles are still connected by a dimensional bridge-relation which is independent of the degree of Fourier-mode decimation.
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