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Experiments of Air-pocket Movement in an 18.2 degrees downward 240-mm Conduit
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
2012 (English)In: 2012 International Conference On Modern Hydraulic Engineering, Elsevier, 2012, 791-795 p.Conference paper, Published paper (Refereed)
Abstract [en]

Experiments are carried out in a test rig, consisting of a Plexiglas pipe with an inner diameter of 240 mm and an inclination of 18.2o, to investigate air-water two-phase flows in conjunction with bottom spillways. Results show that the critical velocity, which is the minimal water velocity to start moving an air pocket, in the rough pipe, is independent of the air-pocket volume; in the smooth pipe it doesn't increase with increasing diameter as much as the previous researchers indicated. Pipe roughness doesn't affect the velocity of the air-pocket when it moves upstream in the downward inclined pipe.

Place, publisher, year, edition, pages
Elsevier, 2012. 791-795 p.
Series
Procedia Engineering, ISSN 1877-7058 ; 28
Keyword [en]
two-phase flow, air pocket, critical velocity, roughness effect, diameter effect
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-52309DOI: 10.1016/j.proeng.2012.01.811ISI: 000306529200137Scopus ID: 2-s2.0-84863119424OAI: oai:DiVA.org:kth-52309DiVA: diva2:465939
Conference
2012 International Conference on Modern Hydraulic Engineering, CMHE 2012; Nanjing, Jiangsu; 9 March 2012 through 11 March 2012
Note

QC 20111215

Available from: 2011-12-15 Created: 2011-12-15 Last updated: 2012-09-14Bibliographically approved
In thesis
1. Air-pocket transport in conjunction with bottom-outlet conduits for dams
Open this publication in new window or tab >>Air-pocket transport in conjunction with bottom-outlet conduits for dams
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Undesired air entrainment in bottom outlet conduits of dams may cause pressure transients, leading to conduit vibrations, blowback, discharge pulsation and even cavitation, and jeopardize the operational safety. Due to design limitations or construction costs, it is impossible to create an air free environment in a pressurized pipe. Therefore, it is essential to understand the air transport in enclosed pipes in order to provide guidance in bottom outlet design and operation. The commonly used criterion of the air-pocket movement in pipe flow is the water flow velocity for starting moving an air pocket, the so-called critical velocity.

In this thesis, the classical Volume of Fluid (VOF) model combined with the k-ε turbulence model is adopted for the computation of the critical velocity of a 150-mm pipe. The computed critical velocities are compared with the experimental results. The governing parameters investigated in this study include pipe slope and diameter, wall shear stress and air-pocket volume. Meanwhile, the carrying capacity (air-pocket velocity/ flow velocity) at all pipe slopes are analyzed. The simulation results of air pockets with different volumes in the bottom outlet conduit of Letten Dam in Sweden are presented in this study.

Moreover, experimental study was conducted to measure the critical velocity for a 240-mm Plexiglas pipe. The results are in agreement with the experiments performed by HR Wallingford (HRW) in 2003 in terms of the effects of pipe slope and air-pocket volume; however, the critical Froude pipe number is slightly smaller in this study. In rough pipes, a larger critical velocity is required compared with that in the smooth pipe. The removal mechanism in the rough pipe involves the successive loss of air caused by turbulence. This explains that the air-pocket size, with the dimensionless air-pocket volume n < 0.015, has little impact on the critical velocity for the rough pipe. In addition, roughness has little impact on the air-pocket velocity when it moves upstream in the downward inclined pipe. The trapped air bubbles most likely remain permanently in the rough pipe.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. x, 25 p.
Series
Trita-LWR. LIC, ISSN 1650-8629 ; 2062
Keyword
Air-water two-phase flow, critical velocity, diameter effect, roughness, VOF model, bottom outlet, experiment
National Category
Fluid Mechanics and Acoustics Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-52727 (URN)KTH/LWR/LIC 2062-SE (ISRN)978-91-7501-213-1 (ISBN)
Presentation
2012-01-19, V3, Teknikringen 72, KTH, Stockholm, 10:30 (English)
Opponent
Supervisors
Note
QC 20120110Available from: 2012-01-10 Created: 2011-12-19 Last updated: 2012-01-10Bibliographically approved

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