# Dissipation element analysis of scalar fields in wall-bounded turbulent flow

## Abstract

In order to analyze the geometry of turbulent structures in turbulent channel flow, the scalar field obtained by Direct Numerical Simulations (DNS) is subdivided into numerous finite size regions. In each of these regions local extremal points of the fluctuating scalar are determined via gradient trajectory method. Gradient trajectories starting from every material point in the scalar field Φ(x,y, z, t) in the directions of ascending and descending scalar gradients will always reach a minimum and a maximum point where \nabla Φ = 0. The ensemble of all material points belonging to the same pair of extremal points defines a dissipation element 2. They can be characterized statistically by two parameters: namely the linear length connecting the minimum and maximum points and the absolute value of the scalar difference ΔΦ at these points, respectively. Because material points are space-filling, dissipation elements are also space-filling and unique, which means that the turbulent scalar field can be decomposed into such elements. This allows the reconstruction of certain statistical quantities of small scale turbulence. Here special focus will be given to examine if and how critical points and accordingly dissipation elements are in relationship with the characteristic layers of a turbulent channel flow.

Item Type: Book Section 2009 Tordella, Daniela and Sreenivasan, R. Aldudak, Fettah and Oberlack, Martin Dissipation element analysis of scalar fields in wall-bounded turbulent flow English In order to analyze the geometry of turbulent structures in turbulent channel flow, the scalar field obtained by Direct Numerical Simulations (DNS) is subdivided into numerous finite size regions. In each of these regions local extremal points of the fluctuating scalar are determined via gradient trajectory method. Gradient trajectories starting from every material point in the scalar field Φ(x,y, z, t) in the directions of ascending and descending scalar gradients will always reach a minimum and a maximum point where \nabla Φ = 0. The ensemble of all material points belonging to the same pair of extremal points defines a dissipation element 2. They can be characterized statistically by two parameters: namely the linear length connecting the minimum and maximum points and the absolute value of the scalar difference ΔΦ at these points, respectively. Because material points are space-filling, dissipation elements are also space-filling and unique, which means that the turbulent scalar field can be decomposed into such elements. This allows the reconstruction of certain statistical quantities of small scale turbulence. Here special focus will be given to examine if and how critical points and accordingly dissipation elements are in relationship with the characteristic layers of a turbulent channel flow. Proceedings of EUROMECH Colloquium 512. Small Scale Turbulence and Related Gradient Statistics, Torino, Italy, October 26-29, 2009 Accademia delle Scienze di Torino 8890160845 small scale turbulence; dissipation elements 16 Department of Mechanical Engineering > Fluid Dynamics (fdy)16 Department of Mechanical Engineering 01 Sep 2011 11:14 http://www.accademiadellescienze.it/media/565 T2T_XMLBibTeXSimple MetadataJSONRDF+XMLMODSReference ManagerDublin CoreAtomEP3 XMLHTML CitationEndNoteMultiline CSVASCII Citation TUfind oder in Google
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