Abstract
In this experimental study, the effects of an isolated, cylindrical roughness element on laminar-turbulent transition is investigated and compared to three-dimensional, linear stability theory. Experiments have been done at both sub- and supercritical Reynolds numbers. In the subcritical case, controlled forcing was applied to show that the roughness amplifies unsteady disturbances which can grow large enough to trip the boundary layer. At a higher, but still subcritical Reynolds number, natural disturbances suffice to trip the boundary layer intermittently. Further increase of the Reynolds numbers leads to permanent transition. This transition Reynolds number and dominant frequencies are compared to the critical Reynolds number from theory to provide experimental evidence of a global instability.
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Acknowledgements
The financial support of the Deutsche Forschungsgemeinschaft (DFG) under reference number RI 680/32-1 is gratefully acknowledged for enabling this project. We would like to thank J.-C. Robinet, S. Cherubini and M.J. Kloker for fruitful discussions.
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Puckert, D.K., Rist, U. (2018). Transition Downstream of an Isolated Cylindrical Roughness Element on a Flat Plate Boundary Layer. In: Dillmann, A., et al. New Results in Numerical and Experimental Fluid Mechanics XI. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 136. Springer, Cham. https://doi.org/10.1007/978-3-319-64519-3_27
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DOI: https://doi.org/10.1007/978-3-319-64519-3_27
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