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Occurrence of critical flow depths in compound open channels | |
Author | Roa, Arturo G |
Call Number | AIT Thesis no.WM-96-05 |
Subject(s) | Channels (Hydraulic engineering) |
Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. School of Civil Engineering |
Publisher | Asian Institute of Technology |
Series Statement | Thesis ; no. WM-96-05 |
Abstract | Many experimental researches done over the past decade concerning compound cha1mel flows were focused on quantifying boundary shear stresses, assessment of discharge, velocity distributions and turbulence characteristics. Limited literature describing compotmd chaimel flow regimes were presented without sufficient experimental evidence as to their validity. The increasing importance and acceptability of compound sections in irrigation systems and flood control structures underlines the need to verify the validity of previously derived methods using experimental data. Experiments were conducted in laboratory compound flume 1.80 m wide and 12.00 m long to verify the four existing Froude number models. In the experimental investigation, the Froude number models were classified according to the inherent approach in their derivation i.e., momentum approach, specific energy approach and discharge weighted Froude number. 864 flume tests under 70 different discharge values covering nine cross sectional configurations of different cross sectional geometry were tested. To investigate the role of interaction between the main channel and berm flow, the area correction proposed by Holden (1986) to account for the shear stresses at the main channel and berm interfaces were incorporated in the Froude number models. The use of area correction in discharge computation resulted in a better proportions of flow under interacting condition in compound open channel flows. Conventional method of mean velocity computation was found to be inadequate to represent the mean velocity in compound open channel flow. Moreover, the use of velocity correction coefficient a resulted in corrected average velocities which are higher than the velocity in the main channel and berm. The method proposed by Chaudhry and Bhallamudi (1988), Blalock and Sturm (1982) and Konemann (1982) resulted in a higher computed Froude number for compound open channel flow. This is due to improper representation of the average velocity from the conventional method. The above mentioned methods can, however be used to describe the flow regime at flow depths equal to or greater than the depth defined by the point of convergence of the berm and main channel relative velocities. The discharge weighted Froude number proposed by Petryk and Grant (1978) shows a closer agreement of the subsection Froude numbers. The flow interaction between main channel and berm tend to reduce the computed critical depth. The downward shift in Froude number curve is more noticeable for lower flow depth above the berm indicating a higher rate of flow interaction. The flow interaction was found to increase with an increase in berm main channel width ratio. |
Year | 1996 |
Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. WM-96-05 |
Type | Thesis |
School | School of Civil Engineering |
Department | Department of Civil and Infrastucture Engineering (DCIE) |
Academic Program/FoS | Water Engineering and Management (WM) |
Chairperson(s) | Tawatchai Tingsanchali; |
Examination Committee(s) | Sutat Weesakul;Kyotoh, Harumitchi; |
Scholarship Donor(s) | The Royal Danish Government ( DANIDA); |
Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1996 |