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Characteristics of Flow past Warped and Wedge Transitions


Characteristics of Flow past Warped and Wedge Transitions

Thapa, Devi Ram (2017) Characteristics of Flow past Warped and Wedge Transitions. PhD thesis, Concordia University.

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Expanding channel transitions link the subcritical flow emerging from reservoirs to narrow concrete rectangular channels connected to very wide trapezoidal earth channels of irrigation networks. The present study includes the effects of various design changes in warped and wedge transitions on the behavior of flow emerging from transitions. The efficiency of a good transition is measured in terms of its ability to provide a low value for the maximum velocity and a nearly uniform velocity distribution at the transition exit section. Also, a well-designed transition reduces an energy loss in the transition and ensures that the secondary flow intensity in the downstream trapezoidal channel is low enough to avoid the channel boundary erosion. The study indicated that the changes made in the design of warped and wedge transitions did achieve these stated objectives.
A LDA was used to measure the flow velocity. The point measurements were non-intrusive, and provided a three-dimensional distributions graph of the mean flow velocity as well as the intensity of turbulent fluctuations. The data determined by LDA as well as the depth data form point gauge measurement yielded the longitudinal flow profile and the maximum velocity ratio, as well as the head loss in the transition and the intensity of secondary flow. Flow separation characteristics were recorded by tracing the separation zone and the points of reattachment based on velocity data. These were confirmed by visual observation involving dye tests. The information provided assists field engineer to design efficient transition. Simple appurtenances such as vanes in warped transition and short streamlining strips along the diagonal of wedge transition were shown to be effective in improving the transition efficiency measured in terms of reducing flow separation and conserving energy.
The 3-D model tested was successful in quantifying the effects of vanes in warped transitions. To simulate the complex flow in the warped transition, RNG k-ε and RSM models were adopted and the results were validated by using the available experimental data for a warped transition. It is shown that the use of a vane effectively reduces flow separation and eddy motion in the transition and downstream channel.

Divisions:Concordia University > Gina Cody School of Engineering and Computer Science > Building, Civil and Environmental Engineering
Item Type:Thesis (PhD)
Authors:Thapa, Devi Ram
Institution:Concordia University
Degree Name:Ph. D.
Program:Civil Engineering
Date:6 November 2017
Thesis Supervisor(s):Li, S. S. and Ramamurthy, A. S.
Keywords:Warped transition; Wedge transition; Modified wedge transition; Flow separation; Secondary flow; Head loss; Laser Doppler Anemometry measurements; Open channel flow; Hydraulics; Hydraulic design; Experimentation.
ID Code:983337
Deposited By: DEVI RAM THAPA
Deposited On:05 Jun 2018 14:04
Last Modified:05 Jun 2018 14:04


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