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Transition flow regime on stepped spillways: air–water flow characteristics and step-cavity fluctuations

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Abstract

Stepped spillways are man-made hydraulic structures designed to control the release of flow and to achieve a high energy dissipation. The flow pattern for a given stepped chute geometry can be distinguished into different regimes. Herein, the transition flow regime occurs at a range of intermediate discharges and is characterised by strong hydrodynamic fluctuations and intense splashing next to the free-surface. Up to date, only minimal experimental data is available for the transition flow. As this flow regime is likely to occur on stepped spillways designed for skimming flow operation, a knowledge of the transition flow characteristics is important to ensure safe operation. The present article investigates the hydraulics of the transition flow regime on a laboratory spillway, presenting a detailed characterisation of air–water flow properties and an image-based analysis of pool depth fluctuations within successive step-cavities. The results show two different void fraction and turbulence intensity profiles, indicating the existence of an upper and a lower transition flow sub-regime. The image-based analysis suggests the presence of a rapidly and a gradually varied flow region downstream of the inception point for both sub-regimes, whereas full equilibrium flow was not reached in the physical model. Overall, the study contributes towards improving the characterisation of the transition flow by assembling analytical solutions for different two-phase flow parameters, including void fraction, interfacial velocity and step-cavity pool height.

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Acknowledgements

The authors acknowledge the technical assistance of Jason Van Der Gevel and Stewart Matthews (The University of Queensland). Matthias Kramer was supported by DFG Grant No. KR 4872/2-1.

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Authors and Affiliations

  1. School of Civil Engineering, The University of Queensland, Brisbane, QLD, 4072, Australia

    Matthias Kramer & Hubert Chanson

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  1. Matthias Kramer
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  2. Hubert Chanson
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Correspondence to Matthias Kramer.

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Kramer, M., Chanson, H. Transition flow regime on stepped spillways: air–water flow characteristics and step-cavity fluctuations. Environ Fluid Mech 18, 947–965 (2018). https://doi.org/10.1007/s10652-018-9575-y

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  • DOI: https://doi.org/10.1007/s10652-018-9575-y

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