Time-varying secondary flows in turbulent boundary layers over surfaces with spanwise heterogeneity
ORAL
Abstract
Secondary flows form in turbulent flow over surfaces with spanwise heterogeneity. In this study, we use surfaces comprised of spanwise alternating smooth and rough (P-36 grit sandpaper) strips to investigate the behaviour of these secondary flows for various strip widths. PIV measurements are performed on the wall-parallel plane above surfaces with various strip widths $S$ ($0.3 \leq S/\overline{\delta} \leq 3.6$), where $\overline{\delta}$ is the spanwise-averaged boundary layer thickness. We find that, when $S/\overline{\delta} \approx 1$, these secondary flows not only strengthen but also exhibit a pronounced unsteadiness. This unsteadiness is consistent with a flapping from side-to-side of large-scale streaks with a streamwise wavelength of 3-4$\overline{\delta}$.
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Authors
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Dea Wangsawijaya
The University of Melbourne
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Kevin Kevin
The University of Melbourne
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Daniel Chung
Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia, University of Melbourne, The University of Melbourne
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Ivan Marusic
University of Melbourne, Department of Mechanical Engineering, University of Melbourne, Melbourne, Department of Mechanical Engineering, The University of Melbourne, Melbourne, Australia, The University of Melbourne
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Nicholas Hutchins
University of Melbourne, Department of Mechanical Engineering, University of Melbourne, Department of Mechanical Engineering, The University of Melbourne, Melbourne, Australia, The University of Melbourne