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Title:Large-scale modes of turbulent channel flow: transport and stucture
Author(s):Liu, Zi-Chao; Adrian, Ronald J.; Hanratty, Thomas J.
Subject(s):Velocity Fields
Eigenvalue Spectra
Orthongonal Decomposition
Abstract:Turbulent flow in a rec;tangular channel flow is investigated to determine the scale and pattern of the eddies that contribute most to the total turbulent kinetic energy and the Reynolds shear stress. Instantaneous, two-dimensional particle image velocimetry measurements in the streamwisewall- normal plane at Reynolds numbers Reh= 5,378 and 29,935 are used to form two-point spatial correlation functions, from which the proper orthogonal modes are determined. Largescale motions represented by a small set of lower-order eigenmodes contain a large fraction of the kinetic energy of the streamwise velocity component, and a small fraction of the kinetic energy of the wall-normal velocities, consistent with Townsend (1958). Surprisingly, the set of large-scale modes that contain fifty-per cent of the total turbulent kinetic energy in the channel, also contains seventy-five per cent of the total Reynolds shear stress in the outer region. Thus, the large-scale motions dominate turbulent transport in all parts of the channel except the buffer layer. The flow structures are extracted from individual realizations of the flow field by using the dominant eigenfunctions as a low-pass filter. In the streamwise wall-normal plane their pattern often consists of an inclined region of second quadrant vectors separated from an upstream region of fourth quadrant vectors by a stagnation point/shear layer. The inclined Q4/shear/Q2 region of the largest motions extends beyond the centerline of the channel and lies under a region of fluid that rotates about the spanwise direction. Reynolds number similarity of the large structures is demonstrated, approximately, by comparing the two-dimensional correlation coefficients and the eigenvalues of the different modes at the two Reynolds numbers.
Issue Date:2000-02
Publisher:Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report:TAM R 929
Genre:Technical Report
Sponsor:Office of Naval Researchearch; National Science Foundation
Rights Information:Copyright 2000 Board of Trustees of the University of Illinois
Date Available in IDEALS:2021-11-04

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  • Technical Reports - Theoretical and Applied Mechanics (TAM)
    TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.

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