• Shishir Kumar

      Articles written in Pramana – Journal of Physics

    • Large-eddy simulations of fluid and magnetohydrodynamic turbulence using renormalized parameters

      Mahendra K Verma Shishir Kumar

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      In this paper a procedure for large-eddy simulation (LES) has been devised for fluid and magnetohydrodynamic turbulence in Fourier space using the renormalized parameters. The parameters calculated using field theory have been taken from recent papers by Verma [1,2]. We have carried out LES on 643 grid. These results match quite well with direct numerical simulations of 1283. We show that proper choice of parameter is necessary in LES.

    • Local shell-to-shell energy transfer via nonlocal interactions in fluid turbulence

      Mahendra K Verma Arvind Ayyer Olivier Debliquy Shishir Kumar Amar V Chandra

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      In this paper we analytically compute the strength of nonlinear interactions in a triad, and the energy exchanges between wave-number shells in incompressible fluid turbulence. The computation has been done using first-order perturbative field theory. In three dimensions, magnitude of triad interactions is large for nonlocal triads, and small for local triads. However, the shell-to-shell energy transfer rate is found to be local and forward. This result is due to the fact that the nonlocal triads occupy much less Fourier space volume than the local ones. The analytical results on three-dimensional shell-to-shell energy transfer match with their numerical counterparts. In two-dimensional turbulence, the energy transfer rates to the nearby shells are forward, but to the distant shells are backward; the cumulative effect is an inverse cascade of energy.

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