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CROSS-FLOW STEREO PIV MEASUREMENTS IN WALL TURBULENCE

J. M. Barros
Department of Mechanical Science and Engineering University of Illinois Urbana, IL 61801 USA

Kenneth T. Christensen
Laboratory for Turbulence and Complex Flow Department of Theoretical and Applied Mechanics University of Illinois at Urbana-Champaign, Urbana, IL 61801 USA; Aerospace and Mechanical Engineering; Civil & Environmental Engineering & Earth Sciences University of Notre Dame Notre Dame, Indiana, USA 46556

Аннотация

Wide field of view stereo PIV measurements were conducted in the wall-normal-spanwise plane of fully-developed turbulent channel flow. These experiments represent a significant challenge to the stereo PIV method as the dominant velocity component was oriented normal to the PIV measurement plane while the in-plane components were predominantly much weaker turbulent fluctuations. Nevertheless, these measurements agreed well with DNS results at a similar Reynolds number, both in the mean streamwise velocity as well as the Reynolds normal and shear stresses, which validated the experimental methodology employed. Inspection of instantaneous velocity fields in this cross plane uncovered the spatial signatures of low- and high-momentum regions, the former of which have been previously linked to hairpin vortex packets in the outer layer of wall turbulence. POD was employed to study the spatial characteristics of the large-scale motions further and revealed a significant spanwise coherence in the form of alternating low- and high-momentum regions well beyond that reflected in two-point velocity correlations.