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Backflow phenomenon in converging and diverging channels

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Abstract

To date, a backflow phenomenon that occurs in subsonic zero-pressure-gradient and adverse-pressure-gradient turbulent boundary layers has been well studied and its existence in such flow types is beyond doubt. In the present investigation, focusing on a turbulent air flow in a duct with adjustable cross section, for the first time we provide experimental evidence for the existence of backflow events in a converging channel and demonstrate the possibility of their occurrence in a favorable-pressure-gradient turbulent boundary layer. Taking into account that the backflow events are characterized by the low probability of their occurrence and spatio-temporal extent at the level of the Kolmogorov scale, we pay special attention to the use of high-speed particle image velocimetry with high spatio-temporal resolution. The measurement results revealed a general tendency in the backflow formation mechanism in the considered flow regimes and channel configurations. In conjunction with the findings of other studies, we suggest that the backflow events are induced by transversely oriented vortices located in the buffer region of the turbulent boundary layer and formed as a result of the interaction of large-scale high-momentum and low-momentum flow regions.

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The dataset obtained during the current study is not publicly available but are available from the corresponding author on reasonable request.

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Acknowledgements

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Funding

Numerical simulations and data analysis were supported by the Ministry of Science and Higher Education of the Russian Federation (agreement No. 075-15-2020-806). Experiments were conducted within the Russian Science Foundation grant no. 22-19-00507.

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Contributions

D.Z. and A.S. designed the test section of the experimental setup and carried out the experiments. D.Z. and A.L. processed all the experimental results and discovered the backflow phenomenon in a converging channel. E.I. and R.M. performed RANS simulations. Analysis and interpretation of the results were carried out by D.Z., R.L. and D.M. D.Z. wrote an original draft of the manuscript. All authors reviewed the manuscript.

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Correspondence to Dinar Zaripov or Renfu Li.

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Zaripov, D., Li, R., Lukyanov, A. et al. Backflow phenomenon in converging and diverging channels. Exp Fluids 64, 9 (2023). https://doi.org/10.1007/s00348-022-03536-0

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  • DOI: https://doi.org/10.1007/s00348-022-03536-0

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