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Dynamics and decay of a spherical region of turbulence in free space

Yu, Ke and Colonius, Tim and Pullin, D. I. and Winckelmans, Grégoire (2020) Dynamics and decay of a spherical region of turbulence in free space. . (Unpublished) https://resolver.caltech.edu/CaltechAUTHORS:20201012-140154360

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Abstract

We perform direct numerical simulation (DNS) and large eddy simulation (LES) of an initially spherical region of turbulence evolving in free space. The computations are performed with a lattice Green's function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. LES simulations are conducted with the stretched vortex sub-grid stress model. The initial condition is spherically windowed, isotropic homogeneous incompressible turbulence. We study the spectrum and statistics of the decaying turbulence and compare the results with decaying isotropic turbulence, including cases representing different low wavenumber behavior of the energy spectrum (i.e. k² versus k⁴). At late times the turbulent sphere expands with both mean radius and integral scale showing similar time-wise growth exponents. The low wavenumber behavior has little effect on the inertial scales, and we find that decay rates follow Saffman (1967) predictions in both cases, at least until about 400 initial eddy turnover times. The boundary of the spherical region develops intermittency and features ejections of vortex rings. These are shown to occur at the integral scale of the initial turbulence field and are hypothesized to occur due to a local imbalance of impulse on this scale.


Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/2009.10364arXivDiscussion Paper
ORCID:
AuthorORCID
Yu, Ke0000-0003-0157-4471
Colonius, Tim0000-0003-0326-3909
Additional Information:This work was supported by the ONR grant No. N00014-16-1-2734 and the AFOSR/UCLA grant No. FA9550-18-1-0440.
Group:GALCIT
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-16-1-2734
Air Force Office of Scientific Research (AFOSR)FA9550-18-1-0440
Record Number:CaltechAUTHORS:20201012-140154360
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201012-140154360
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105988
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:12 Oct 2020 21:09
Last Modified:18 Nov 2020 19:54

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