Abstract
Controlling freestream turbulence (FST) in low-turbulence wind or water channels is a common challenge and often difficult to achieve. Particularly at low velocities, design guidelines from literature may not fulfill their purpose and thus require alternative strategies. In this study, we propose the installation of a fine-meshed screen downstream of the contraction and not in the settling chamber as typically advised in literature. With this strategy, the lower operational limitation of our facility could be extended below \(U_{\infty }= 0.06\,\text {ms}^{-1}\) and the turbulence intensity reduced by \(60 \%\) at 0.04 ms\(^{-1}\). This is not only an improvement of freestream conditions but also the key to experiments in the laminar boundary layer, which is highly sensitive to FST. In fact, two fundamentally different transition mechanism can be distinguished with this approach.
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Acknowledgements
The financial support of the Deutsche Forschungsgemeinschaft (DFG) under reference number RI 680/32-1 is gratefully acknowledged for enabling this project. We would like to thank Y. S. Kachanov for the correspondence.
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Puckert, D.K., Dieterle, M. & Rist, U. Reduction of freestream turbulence at low velocities. Exp Fluids 58, 45 (2017). https://doi.org/10.1007/s00348-017-2333-y
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DOI: https://doi.org/10.1007/s00348-017-2333-y