Abstract
Hairpin structures in the outer region of a turbulent boundary layer subjected to a strong adverse pressure gradient have been studied using PIV with inclined spanwise planes. This work is a follow-up to the study of Maciel and Shafiei Mayam (iTi Conference on Turbulence III, Bertinoro, Italy, October 12–15, 2008) done in the same flow but with streamwise/wall-normal planes. In agreement with Maciel and Shafiei Mayam, it is found that the gross features of the hairpin vortices and packets in the outer region above 0.2δ do not differ significantly from those found in a zero-pressure-gradient turbulent boundary layer at a comparable Reynolds number. In both flows, two-legged hairpins although asymmetric occur more frequently than one-legged ones and the outer-scaled hairpin width distributions are similar with a mean width of 0.15δ. The results suggest however finer legs of higher swirl in the zero-pressure-gradient case. In accord with Maciel and Shafiei Mayam, the streamwise separation between hairpins is smaller in the present decelerated flow.
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Acknowledgements
Financial support from NSERC and CFI of Canada is gratefully acknowledged by the authors. They also wish to thank N. Hutchins, W.T. Hambleton and I. Marusic for sharing their data, as well as M.H. Shafiei Mayam and D. Lopez for their help with the measurements and data processing.
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Rahgozar, S., Maciel, Y. (2011). Spanwise Characteristics of Hairpin Packets in a Turbulent Boundary Layer Under a Strong Adverse Pressure Gradient. In: Stanislas, M., Jimenez, J., Marusic, I. (eds) Progress in Wall Turbulence: Understanding and Modeling. ERCOFTAC Series, vol 14. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-9603-6_18
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DOI: https://doi.org/10.1007/978-90-481-9603-6_18
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