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Three-Dimensional Computations Of Water-Air Flow In A Bottom Spillway During Gate Opening
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
2014 (Engelska)Ingår i: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 8, nr 1, s. 104-115Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Undesired entrainment of air in a bottom spillway often leads to problems in both safety and operational functions. A numerical analysis of a transient process of air entrainment into bottom spillway flows when a spillway gate is opened was conducted in this study. The Volume of Fluid (VOF) model was used. The 3D computational domain consisted of a spillway conduit, a moving bulkhead gate, a gate shaft, an upstream reservoir and a downstream outlet. The large number of cells, together with the dynamic mesh modelling of the moving gate, required substantial computational resources, which necessitated parallel computing on a mainframe computer. The simulations captured the changes in the flow patterns and predicted the amount of air entrainment in the gate shaft and the detrainment downstream, which help in the understanding of the system behaviour during opening of the spillway gate. The initial conduit water level and the gate opening procedure affect the degree of air entrainment in the gate shaft. To release the undesired air, a de-aeration chamber with a tube leading to the atmosphere was added to the conduit. Despite the incomplete air release, the de-aeration chamber was found to be effective in reducing water surface fluctuations in the downstream outlet.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2014. Vol. 8, nr 1, s. 104-115
Nyckelord [en]
bottom spillway, moving gate, air entrainment, two-phase flow, CFD
Nationell ämneskategori
Vattenteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-141194ISI: 000332216500009Scopus ID: 2-s2.0-84896998070OAI: oai:DiVA.org:kth-141194DiVA, id: diva2:695573
Anmärkning

QC 20140211

Tillgänglig från: 2014-02-11 Skapad: 2014-02-11 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
Ingår i avhandling
1. Modelling air―water flows in bottom outlets of dams
Öppna denna publikation i ny flik eller fönster >>Modelling air―water flows in bottom outlets of dams
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
KTH Royal Institute of Technology, 2014. s. xiv, 32
Serie
TRITA-LWR. PHD, ISSN 1650-8602 ; 2014:02
Nyckelord
Air pocket, Air entrainment, Bottom outlet, Critical velocity, Critical submergence, CFD, Experiment, Vortex, PIV, Two-phase air―water flow
Nationell ämneskategori
Samhällsbyggnadsteknik
Forskningsämne
Mark- och vattenteknik; Byggvetenskap
Identifikatorer
urn:nbn:se:kth:diva-141182 (URN)978-91-7595-017-4 (ISBN)
Disputation
2014-02-28, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20140211

Tillgänglig från: 2014-02-11 Skapad: 2014-02-11 Senast uppdaterad: 2014-02-11Bibliografiskt granskad

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