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Effects of intake-entrance profiles on free-surface vortices
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
National Chung Tsing University, Taiwan.
2014 (English)In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 52, no 4, 523-531 p.Article in journal (Refereed) Published
Abstract [en]

Intake free-surface vortices can cause efficiency losses, flow fluctuations and even structural damages. Experiments were performed to examine the effect of entrance shapes on the critical submergence. Seven entrance shapes were devised and tested, including a square-edged, a bell-mouthed, three symmetrical conical and two conical profiles with eccentricity. The focus of the study was on a range of Froude numbers from 0.25 to 0.65. The square-edged shape appeared to show the highest local head-loss compared to other shapes. Steady counter-clockwise vortices characterize all the intake profiles except in a narrow water tank. The experiments show both discrepancy and similarity between the intake profiles. The critical submergence of the bell-mouthed intake is lower when compared to the square-edged shape. For the other profiles, it is proportional to the Froude number. A closer sidewall may lead to larger critical submergence in the case of weak circulations. The results demonstrate that the intake-entrance profile has an important effect on the critical submergence.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2014. Vol. 52, no 4, 523-531 p.
Keyword [en]
Critical submergence, downward intake, entrance profile, free-surface vortex, Froude number
National Category
Water Engineering
URN: urn:nbn:se:kth:diva-141190DOI: 10.1080/00221686.2014.905504ISI: 000341847100009ScopusID: 2-s2.0-84912001646OAI: diva2:695546

QC 20160104

Available from: 2014-02-11 Created: 2014-02-11 Last updated: 2016-01-04Bibliographically approved
In thesis
1. Modelling air―water flows in bottom outlets of dams
Open this publication in new window or tab >>Modelling air―water flows in bottom outlets of dams
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

If air is entrained in a bottom outlet of a dam in an uncontrolled way, the resulting air pockets may cause problems such as blowback, blowout and loss of discharge capacity. In order to provide guidance for bottom outlet design and operation, this study examines how governing parameters affect air entrainment, air-pocket transport and de-aeration and the surrounding flow structure in pipe flows. Both experimental and numerical approaches are used.

Air can be entrained into the bottom outlet conduit due to vortex formation at the intake if the intake submergence is not sufficient. The influent of the intake entrance profiles and channel width on the critical submergence were studied in the experiment.

The experimental study was performed to investigate the incipient motion of air pockets in pipes with rectangular and circular cross sections. The critical velocity is dependent on pipe slope, pipe diameter, pipe roughness and air-pocket volume. If the pipe is horizontal, air removal is generally easier in a rectangular pipe than in a circular pipe. However, if the pipe is downward-inclined, air removal is easier in a circular pipe.

When a bottom outlet gate opens, air can become entrained into the conduit in the gate shaft downstream of the gate. Using FLUENT software, the transient process of air entrainment into a prototype bottom outlet during gate opening is simulated in three dimensions. The simulations show in the flow-pattern changes in the conduit and the amount of air entrainment in the gate shaft. The initial conduit water level affects the degree of air entrainment. A de-aeration chamber is effective in reducing water surface fluctuations at blowout.

High-speed particle image velocimetry (HSPIV) were applied to investigate the characteristics of the flow field around a stationary air pocket in a fully developed horizontal pipe flow. The air pocket generates a horseshoe vortex upstream and a reverse flow downstream. A shear layer forms from the separation point. Flow reattachment is observed for large air pockets. The air―water interface moves with the adjacent flow. A similarity profile is obtained for the mean streamwise velocity in the shear layer beneath the air pocket.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2014. xiv, 32 p.
TRITA-LWR. PHD, ISSN 1650-8602 ; 2014:02
Air pocket, Air entrainment, Bottom outlet, Critical velocity, Critical submergence, CFD, Experiment, Vortex, PIV, Two-phase air―water flow
National Category
Civil Engineering
Research subject
Land and Water Resources Engineering; Civil and Architectural Engineering
urn:nbn:se:kth:diva-141182 (URN)978-91-7595-017-4 (ISBN)
Public defence
2014-02-28, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)

QC 20140211

Available from: 2014-02-11 Created: 2014-02-11 Last updated: 2014-02-11Bibliographically approved

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