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On the impact of the turbulent/non-turbulent interface on differential diffusion in a turbulent jet flow

Hunger, F. and Gauding, M. and Hasse, C. (2016):
On the impact of the turbulent/non-turbulent interface on differential diffusion in a turbulent jet flow.
In: Journal of Fluid Mechanics, Cambridge Univ. Press, pp. 1-12, 802, ISSN 1469-7645,
DOI: 10.1017/jfm.2016.471,
[Online-Edition: http://journals.cambridge.org/article_S0022112016004717],
[Article]

Abstract

The effect of differential diffusion of two passive scalars having Schmidt numbers of unity and 0.25, respectively, is investigated using direct numerical simulation of a temporally evolving jet. The objective of the research is twofold: (i) to compare the turbulent/non-turbulent (T/NT) interface position using the scalar criterion between the unity- and low-Schmidt-number scalar; and (ii) to determine the impact of the T/NT interface on differential diffusion. For the latter, the T/NT interface is detected using the vorticity criterion. To quantify the effect of differential diffusion, a normalised differential diffusion parameter is analysed, clearly showing the dominance of differential diffusion at the T/NT interface. A transport equation for the scalar differences is then evaluated, which shows that differential diffusion originates at the interface. Further, the separation between the passive scalars, arising due to differential diffusion, is studied using conventional and conditional statistics with respect to the interface distance. Since differential diffusion is known to be present at large and small scales, the connection between them is analysed using the scalar dissipation rate. Moreover, the physical mechanism responsible for the departure of the two scalars is analysed using the scalar gradient alignment, the ratio of the diffusive fluxes and by a transport equation for the scalar gradients.

Item Type: Article
Erschienen: 2016
Creators: Hunger, F. and Gauding, M. and Hasse, C.
Title: On the impact of the turbulent/non-turbulent interface on differential diffusion in a turbulent jet flow
Language: English
Abstract:

The effect of differential diffusion of two passive scalars having Schmidt numbers of unity and 0.25, respectively, is investigated using direct numerical simulation of a temporally evolving jet. The objective of the research is twofold: (i) to compare the turbulent/non-turbulent (T/NT) interface position using the scalar criterion between the unity- and low-Schmidt-number scalar; and (ii) to determine the impact of the T/NT interface on differential diffusion. For the latter, the T/NT interface is detected using the vorticity criterion. To quantify the effect of differential diffusion, a normalised differential diffusion parameter is analysed, clearly showing the dominance of differential diffusion at the T/NT interface. A transport equation for the scalar differences is then evaluated, which shows that differential diffusion originates at the interface. Further, the separation between the passive scalars, arising due to differential diffusion, is studied using conventional and conditional statistics with respect to the interface distance. Since differential diffusion is known to be present at large and small scales, the connection between them is analysed using the scalar dissipation rate. Moreover, the physical mechanism responsible for the departure of the two scalars is analysed using the scalar gradient alignment, the ratio of the diffusive fluxes and by a transport equation for the scalar gradients.

Journal or Publication Title: Journal of Fluid Mechanics
Volume: 802
Publisher: Cambridge Univ. Press
Uncontrolled Keywords: jets, turbulent mixing
Divisions: 16 Department of Mechanical Engineering > Simulation of reactive Thermo-Fluid Systems (STFS)
16 Department of Mechanical Engineering
Date Deposited: 15 Nov 2017 15:14
DOI: 10.1017/jfm.2016.471
Official URL: http://journals.cambridge.org/article_S0022112016004717
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