Summary
A comparison is presented of experimental results such as pressure, skin friction (mean and higher moments), and reverse-flow factor to demonstrate the differences between weak and strong closed reverse-flow regions. The driving mechanisms are shear stress or pressure combined with shear stress, causing clearly distinctive distributions of the mean skin friction and its intensity. The “failure” of the reverse-flow parameter reaching 100% in the centre of the separation bubble can be explained by lumps of the free shear layer penetrating to the wall from above and flowing partly downstream near the wall. The outer layer flow structures interact with near-wall streaky structures moving upstream which differ considerably in width and length from those observed in boundary layers. These structures are shown by spanwise correlation measurements and by flow visualization. Suggestions are made for model flows covering weak and strong reverse-flow regions, respectively.
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Fernholz, H.H. (1994). Near-wall phenomena in turbulent separated flows. In: Schnerr, G.H., Bohning, R., Frank, W., Bühler, K. (eds) Fluid- and Gasdynamics. Acta Mechanica, vol 4. Springer, Vienna. https://doi.org/10.1007/978-3-7091-9310-5_7
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DOI: https://doi.org/10.1007/978-3-7091-9310-5_7
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