Article (Scientific journals)
Re-Aeration on Stepped Spillways with Special Consideration of Entrained and Entrapped Air
Bung, Daniel B.; Valero Huerta, Daniel
2018In Geosciences, 8 (9), p. 333
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Keywords :
gas transfer; stepped spillways; skimming flows; self-aeration; air-water interface
Abstract :
[en] As with most high-velocity free-surface flows, stepped spillway flows become self-aerated when the drop height exceeds a critical value. Due to the step-induced macro-roughness, the flow field becomes more turbulent than on a similar smooth-invert chute. For this reason, cascades are oftentimes used as re-aeration structures in wastewater treatment. However, for stepped spillways as flood release structures downstream of deoxygenated reservoirs, gas transfer is also of crucial significance to meet ecological requirements. Prediction of mass transfer velocities becomes challenging, as the flow regime differs from typical previously studied flow conditions. In this paper, detailed air-water flow measurements are conducted on stepped spillway models with different geometry, with the aim to estimate the specific air-water interface. Re-aeration performances are determined by applying the absorption method. In contrast to earlier studies, the aerated water body is considered a continuous mixture up to a level where 75% air concentration is reached. Above this level, a homogenous surface wave field is considered, which is found to significantly affect the total air-water interface available for mass transfer. Geometrical characteristics of these surface waves are obtained from high-speed camera investigations. The results show that both the mean air concentration and the mean flow velocity have influence on the mass transfer. Finally, an empirical relationship for the mass transfer on stepped spillway models is proposed.
Research center :
UEE - Urban and Environmental Engineering - ULiège
Disciplines :
Civil engineering
Author, co-author :
Bung, Daniel B.;  Aachen University of Applied Sciences (FH Aachen) > Hydraulic Engineering Section (HES)
Valero Huerta, Daniel ;  Université de Liège - ULiège > Form. doct. sc. ingé. & techn. (archi., gén. civ. - paysage)
Language :
English
Title :
Re-Aeration on Stepped Spillways with Special Consideration of Entrained and Entrapped Air
Publication date :
05 September 2018
Journal title :
Geosciences
eISSN :
2076-3263
Publisher :
MDPI Open Access Publishing, Basel, Switzerland
Special issue title :
Beyond the Channel—Investigating Processes at Crucial Fluvial Interfaces
Volume :
8
Issue :
9
Pages :
333
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 05 September 2018

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