An Experimental Study of Effects of Step Roughness in Skimming Flows on Stepped Chutes

Gonzalez, Carlos A., Takahashi, Masayuki and Chanson, Hubert (2008) An Experimental Study of Effects of Step Roughness in Skimming Flows on Stepped Chutes. Journal of Hydraulic Research, 46 S1: 24-35. doi:10.1111/j.1365-2222.2008.02941.x

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Author Gonzalez, Carlos A.
Takahashi, Masayuki
Chanson, Hubert
Title An Experimental Study of Effects of Step Roughness in Skimming Flows on Stepped Chutes
Journal name Journal of Hydraulic Research   Check publisher's open access policy
ISSN 0022-1686
Publication date 2008
Year available 2008
Sub-type Article (original research)
DOI 10.1111/j.1365-2222.2008.02941.x
Open Access Status File (Author Post-print)
Volume 46
Issue S1
Start page 24
End page 35
Total pages 12
Publisher IAHR
Collection year 2008
Language eng
Subject 290000 Engineering and Technology
290800 Civil Engineering
290802 Water and Sanitary Engineering
291803 Turbulent Flows
Abstract On a spillway chute, a stepped design increases the rate of energy dissipation on the chute itself and reduces the size of a downstream energy dissipator. Up to date, the effects of step roughness on the flow properties remain unknown despite the practical relevance to damaged concrete steps, rock chutes and gabions weirs. New measurements were conducted in a large-size laboratory facility with two step conditions (smooth and rough) and three types of step roughness. Detailed air-water flow properties were measured systematically for several flow rates. The results showed faster flow motion on rough step chutes. Although the finding is counter-intuitive, it is linked with the location of the inception point of free-surface aeration being located further downstream than for a smooth stepped chute for an identical flow rate. In the aerated flow region, the velocities on rough-step chutes were larger than those of smooth chute flows for a given flow rate and dimensionless location from the inception point of free-surface aeration both at step edges and between step edges. The results suggest that design guidelines for smooth (concrete) stepped spillway may not be suitable to rough stepped chutes including gabion stepped weirs, and older stepped chutes with damaged steps.
Keyword Stepped spillway
Skimming flow
Step roughness
Air-water flow
Physical modelling
Flow resistance
Form drag
Energy dissipation
Gabion stepped weir
Damaged concrete steps
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Q-Index Code C1
Q-Index Status Provisional Code
Additional Notes The full bibliographic details are : GONZALEZ, C.A., TAKAHASHI, M., and CHANSON, H. (2008). "An Experimental Study of Effects of Step Roughness in Skimming Flows on Stepped Chutes." Journal of Hydraulic Research, IAHR, Vol. 46, No. Extra Issue 1, pp. 24-35 (ISSN 0022-1686).

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Civil Engineering Publications
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Created: Thu, 17 Apr 2008, 15:17:04 EST by Hubert Chanson on behalf of School of Civil Engineering