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.

*The financial support of the Australian Research Council is gratefully acknowledged.

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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