Towards Modelling the Downstream Development of a Turbulent Boundary Layer Following a Rough-to-Smooth Step Change in Surface Condition
ORAL
Abstract
In this study we examine the effect of both the friction Reynolds number $Re_{\tau}$ and the roughness Reynolds number $k_s^+$ on a turbulent boundary layer following a rough-to-smooth step change in surface condition along the flow direction. To investigate the effect of $Re_{\tau}$, a set of wind-tunnel experiments is conducted at $k_s^+=160$ while $Re_{\tau}$ is varied from 7100 to 21000. Similarly, to examine the dependence on $k_s^+$, a set of measurements is conducted at $Re_{\tau}=14000$ with $k_s^+$ ranging from 110 to 230. Hot-wire profiles are obtained on a logarithmically spaced grid up to 120 boundary-layer thicknesses downstream of the step change, and the local wall-shear stress is measured directly using oil-film interferometry. Using these data, we propose a new model of the recovering mean velocity profile which accounts for the well-known non-equilibrium behaviour of the internal layer. This mean velocity distribution is then evolved downstream of the step change using the integrated streamwise momentum equation to achieve a full prediction of the mean flow recovery.
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Authors
Mogeng Li
University of Melbourne
Charitha de Silva
University of New South Wales, School of Mechanical and Manufacturing Engineering, University of New South Wales, School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Australia
Daniel Chung
Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia, University of Melbourne, The University of Melbourne
Dale I. Pullin
California Institute of Technology
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
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
