Study of the Streamwise Evolution of Turbulent Boundary Layers to High Reynolds Numbers

Abstract

We consider the streamwise evolution of zero-pressure-gradient (ZPG) turbulent boundary layers developing on the smooth floor of the Melbourne wind tunnel. The flat plate extends over 27 m, and three different tripping devices are used to set the initial conditions. The first trip consists of standard sandpaper, and the second and third trips consist of the addition of threaded rods of diameter 6 and 10 mm, respectively, that lead to “over-tripped” conditions. Fixed Reynolds number per metre U _∞ ∕ν, where U _∞  ≈ 20 m/s is the free-stream velocity and ν is kinematic viscosity, is maintained with a well-established ZPG for all tripping configurations. As the boundary layer evolves along the length of the tunnel floor, the mean velocity profiles are found to approach a constant wake parameter $\Pi$ (as suggested by Coles [7]) for all the three tripping configurations after a sufficient distance downstream of the tripping devices. The broadband turbulence intensities and higher-order moments are found to show variations up the same streamwise distance, here corresponding to O(2000) trip-height lengths downstream of the trips. Further downstream the boundary layers appear to be independent of initial upstream condition and reach converged states. The discussion is aided by computations based on a modified approach originally described by Perry et al. [17], where given an initial upstream mean velocity profile, mean flow parameters are computed for different streamwise stations. The results are shown to compare well with the experimental results.