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Journal of Zhejiang University SCIENCE A 2005 Vol.6 No.3 P.243~250

10.1631/jzus.2005.A0243


Physical modelling and scale effects of air-water flows on stepped spillways


Author(s):  CHANSON Hubert, GONZALEZ Carlos A.

Affiliation(s):  Dept of Civil Engineering, The University of Queensland, Brisbane 4072, Australia

Corresponding email(s):   h.chanson@uq.edu.au

Key Words:  Physical modelling, Scale effects, Stepped spillways, Air entrainment, Air-water flow measurements


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CHANSON Hubert, GONZALEZ Carlos A.. Physical modelling and scale effects of air-water flows on stepped spillways[J]. Journal of Zhejiang University Science A, 2005, 6(3): 243~250.

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author="CHANSON Hubert, GONZALEZ Carlos A.",
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%A GONZALEZ Carlos A.
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%I Zhejiang University Press & Springer
%DOI 10.1631/jzus.2005.A0243

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T1 - Physical modelling and scale effects of air-water flows on stepped spillways
A1 - CHANSON Hubert
A1 - GONZALEZ Carlos A.
J0 - Journal of Zhejiang University Science A
VL - 6
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SP - 243
EP - 250
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PB - Zhejiang University Press & Springer
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DOI - 10.1631/jzus.2005.A0243


Abstract: 
During the last three decades, the introduction of new construction materials (e.g. RCC (Roller Compacted Concrete), strengthened gabions) has increased the interest for stepped channels and spillways. However stepped chute hydraulics is not simple, because of different flow regimes and importantly because of very-strong interactions between entrained air and turbulence. In this study, new air-water flow measurements were conducted in two large-size stepped chute facilities with two step heights in each facility to study experimental distortion caused by scale effects and the soundness of result extrapolation to prototypes. Experimental data included distributions of air concentration, air-water flow velocity, bubble frequency, bubble chord length and air-water flow turbulence intensity. For a Froude similitude, the results implied that scale effects were observed in both facilities, although the geometric scaling ratio was only Lr=2 in each case. The selection of the criterion for scale effects is a critical issue. For example, major differences (i.e. scale effects) were observed in terms of bubble chord sizes and turbulence levels although little scale effects were seen in terms of void fraction and velocity distributions. Overall the findings emphasize that physical modelling of stepped chutes based upon a Froude similitude is more sensitive to scale effects than classical smooth-invert chute studies, and this is consistent with basic dimensional analysis developed herein.

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