Wind-Tunnel Experiment on Logarithmic-Layer Turbulence under the Influence of Overlying Detached Eddies |
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| Authors: | Yasuo Hattori Chin-Hoh Moeng Hitoshi Suto Nobukazu Tanaka Hiromaru Hirakuchi |
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| Institution: | (1) Department of Earth Sciences, Meteorology, Uppsala University, Uppsala, Sweden |
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| Abstract: | A wind-tunnel experiment was carried out to test a hypothesis that the turbulence characteristics in the near-neutral surface
layer are largely determined by detached eddies from above. The surrogate detached eddies were generated by using an active
turbulence grid installed at the front of the test section and the parameters of the grid were chosen such that the fully
developed logarithmic layer downstream consists of a turbulent flow that has similar normalized intensity to that typically
observed in the near-neutral atmospheric surface layer. The effects of the detached eddies on turbulence characteristics were
investigated by comparison with a second experiment without detached eddies. The influence of the detached eddies on the logarithmic
layer was mostly on the coherent structures; the logarithmic layer with the detached eddies revealed a multi-layer structure
similar to that found in the atmosphere where the lower part of the surface layer is dominated by sweep-like events and the
upper part by ejection-like events. Our experiments show that the mean velocity gradient and the Reynolds shear stress were,
however, not affected significantly by the detached eddies and hence the eddy viscosity. |
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