Investigation of three-dimensionality in the near field of a round jet by stereo PIV
by
Ganapathisubramani, B., Longmire, E.K., and Marusic, I
in
Journal of Turbulence, 3, 16, 2002.
Category: Journal Article
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Abstract:
Stereoscopic particle image velocimetry (PIV) measurements are made in streamwise– spanwise and inclined cross-stream planes (inclined at 45◦ and 135◦ to the principal flow direction) of a turbulent boundary layer at moderate Reynolds number (Reτ ∼ 1100). Two-point spatial velocity correlations computed using the PIV data reveal results that are consistent with an earlier study in which packets of hairpin vortices were identified by a feature-detection algorithm in the log region, but not in the outer wake region. Both streamwise–streamwise (Ruu) and streamwise–wall-normal (Ruw) correlations are significant for streamwise displacements of more than 1500 wall units. Zero crossing data for the streamwise fluctuating component u reveal that streamwise strips between zero crossings of 1500 wall units or longer occur more frequently for negative u than positive u, suggesting that long streamwise correlations in Ruu are dominated by slower streamwise structures. Additional analysis of Rww correlations suggests that the long streamwise slow-moving regions 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 are shorter in the streamwise direction and broader in the spanwise direction. Correlations in the inclined cross-stream plane data reveal good agreement with the streamwise–spanwise plane. Ruu in the 45◦ plane is more elongated along the in-plane wall-normal direction than in the 135◦ plane, which is consistent with the presence of hairpin packets with a low-speed region lifting away from the wall.
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