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ANALYSIS OF VORTEX PACKETS AND REYNOLDS STRESS IN A TURBULENT BOUNDARY LAYER

Ellen K. Longmire
Department of Aerospace Engineering and Mechanics, University of Minnesota, 110 Union Street SE, Minneapolis, MN 55455, USA

Bharath Ganapathisubramani
Department of Aerospace Engineering and Mechanics, University of Minnesota 107 Akerman Hall, 110 Union Street SE, Minneapolis, MN 55455, USA; Department of Aeronautics, Imperial College London, Prince Consort Road, London, SW7 2AZ

Ivan Marusic
Department of Mechanical Engineering, The University of Melbourne, Melbourne, VIC, 3010, Australia

Resumo

Sets of stereo PIV measurements were obtained in streamwise-spanwise planes of a turbulent boundary layer with Reτ = 1060. Two-point spatial correlations obtained from fields in the logarithmic region revealed that both streamwise-streamwise (Ruu ) and streamwise-wall-normal (R ) correlations were significant for streamwise displacements of more than 1500 wall units. Zero crossing data for the streamwise fluctuating component u revealed that streamwise strips between zero crossings of 1500 wall units or longer occurred more frequently for negative u than positive u. This result suggested that the long streamwise correlations in Ruu are dominated by slower streamwise structures. Additional analysis of Rσσ correlations suggested that the long slow-moving streamwise structures contain discrete zones of strong upwash over extended streamwise distances as might occur within packets of angled hairpin vortices. At a wall-normal location outside of the log region (z/δ = 0.5), the correlations were shorter in the streamwise direction and broader in the spanwise direction. All of the correlation results are consistent with earlier studies (Ganapathisubramani et al, 2003)in which a feature detection algorithm identified packets of hairpins in the log region but not in the outer region.