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Spectral enstrophy budget in a shear-less flow with turbulent/non-turbulent interface

Cimarelli, Andrea, Cocconi, Giacomo, Fronhapfel, Bettina and De Angelis, Elisabetta 2015. Spectral enstrophy budget in a shear-less flow with turbulent/non-turbulent interface. Physics of Fluids 27 , 125106. 10.1063/1.4937433

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Abstract

A numerical analysis of the interaction between decaying shear free turbulence and quiescent fluid is performed by means of global statistical budgets of enstrophy, both, at the single-point and two point levels. The single-point enstrophy budget allows us to recognize three physically relevant layers: a bulk turbulent region, an inhomogeneous turbulent layer, and an interfacial layer. Within these layers, enstro- phy is produced, transferred, and finally destroyed while leading to a propagation of the turbulent front. These processes do not only depend on the position in the flow field but are also strongly scale dependent. In order to tackle this multi-dimensional behaviour of enstrophy in the space of scales and in physical space, we analyse the spectral enstrophy budget equation. The picture consists of an inviscid spatial cascade of enstrophy from large to small scales parallel to the interface moving towards the interface. At the interface, this phenomenon breaks, leaving place to an anisotropic cascade where large scale structures exhibit only a cascade process normal to the interface thus reducing their thickness while retaining their lengths parallel to the interface. The observed behaviour could be relevant for both the theo- retical and the modelling approaches to flow with interacting turbulent/nonturbulent regions. The scale properties of the turbulent propagation mechanisms highlight that the inviscid turbulent transport is a large-scale phenomenon. On the contrary, the viscous di↵usion, commonly associated with small scale mechanisms, highlights a much richer physics involving small lengths, normal to the interface, but at the same time large scales, parallel to the interface.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Engineering
Subjects: Q Science > QC Physics
T Technology > TJ Mechanical engineering and machinery
Additional Information: Publisher PDF uploaded in accordance with policy at http://www.sherpa.ac.uk/romeo/issn/1057-0829/ [accessed 13/05/2016]
Publisher: American Institute of Physics
ISSN: 1070-6631
Funders: Germany-Israel Foundation for scientific research and development
Date of First Compliant Deposit: 13 May 2016
Date of Acceptance: 15 October 2015
Last Modified: 18 Dec 2017 15:14
URI: http://orca-mwe.cf.ac.uk/id/eprint/90718

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