Kavli Affiliate: Michael P. Brenner
| First 5 Authors: Ryan McKeown, Alain Pumir, Shmuel M. Rubinstein, Michael P. Brenner, Rodolfo Ostilla-Mónico
| Summary:
The transfer of kinetic energy from large to small scales is a hallmark of
turbulent flows. Yet, a precise mechanistic description of this transfer, which
is expected to occur via an energy cascade, is still missing. Several
conceptually simple configurations with vortex tubes have been proposed as a
testing ground to understand the energy cascade. Here, we focus on
incompressible flows and compare the energy transfer occurring in a
statistically steady homogeneous isotropic turbulent (HIT) flow with the
generation of fine-scale motions in configurations involving vortex tubes. We
start by filtering the velocity field in bands of wavenumbers distributed
logarithmically, which allows us to study energy transfer in Fourier space and
also visualize the energy cascade in real space. In the case of a statistically
steady HIT flow at a moderate Reynolds number, our numerical results do not
reveal any significant correlation between regions of intense energy transfers
and vorticity or strain, filtered in corresponding wavenumber bands, nor any
simple self-similar process. In comparison, in the transient turbulent flow
obtained from the interaction between two antiparallel vortex tubes, we observe
a qualitatively simpler organization of the intense structures, as well as of
the energy transfer. The process leading to vortex reconnection via flattening
of interacting vortex cores in two intense ribbons of vorticity, also appears
as qualitatively different from the physics of HIT. Our results indicate that
the specific properties of the transient flows affect the way energy is
transferred, and may not be representative of HIT.
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