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Abstract: Large scale coherent streaks are artificially forced in a well developedturbulent boundary layer at $\Redstar \approx 1000$ using an array ofcylindrical roughness elements. Measures of the velocity field with particleimage velocimetry reveal the presence of well reproducible, streamwiseoriented, steady coherent streaks. We show that the amplitude of these coherentstreaks transiently grows in space. The position of the maximum amplitude isproportional to the spanwise wavelength of the streaks and the most amplifiedspanwise wavelength is of very large scale $\lz \approx 6 \dblo$. These resultsare in good agreement with the recent predictions based on the optimaltransient growth analysis of turbulent mean flows.



Author: Pujals Gregory, Cossu Carlo, Depardon Sebastien

Source: https://arxiv.org/







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