Estimating flow and discharge coefficient equations for Lopac gate in submerged condition

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Yousofvand f.; MONEM M.J.; KAVIANPOUR M.R.

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Journal: IRANIAN WATER RESEARCH JOURNAL Year:2018 | Volume:12 | Issue:2 (29) Page(s): 51-58

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Title

Estimating flow and discharge coefficient equations for Lopac gate in submerged condition

Author(s)

Yousofvand f. | MONEM M.J. | KAVIANPOUR M.R. | Issue Writer Certificate

Keywords

DischargeQ1

Discharge coefficientQ2

Lopac gateQ1

Momentum equationQ2

Submerged flowQ1

Abstract

Lopac gates are considered as water level and flow regulating structures in irrigation canals. Lopac gates are similar to saloon doors, hinged at vertical walls of the canal, which regulate the upstream water level for different Discharges by adjusting their opening angle. Some advantages of this structure could be mentioned as: overflow behavior and better possibility for water level control, simultaneous passage of sediments and floating bodies, low power requirements, and ease of automation of the structure. These advantages have recently attracted the attention of water managers to apply the structure in irrigation canals. Regarding recent application of these structures as control and regulating structures, there are a few hydraulic studies for development of Discharge equation, especially for Submerged flow conditions. In this study, flow characteristics of the Lopac gate are investigated, including Discharge and Discharge coefficient in Submerged flow condition, using laboratory experiments. A laboratory model designed and built in experimental lab of the Water Research Institute, Ministry of Energy, in Tehran. Results of the test which are performed on the gate with the same width as the canal are presented in this paper. Gate was tested for five different opening angles (45, 52. 5, 60, 67. 5 and 70 degrees) and three different Discharges (20, 25 and 30 lit/s). Submergence ratio is defined as the water depth ratio of the downstream to the upstream of the gate (y2/y1). In these experiments, three submergence ratio of 0. 5, 0. 7 and 0. 9 were considered. After regulation the submergence ratio by adjusting the downstream flat sliding gate for specific Discharge and gate opening, and stabilization of the flow conditions in the flume, the upstream and downstream water depth of the gate were measured by point gauge. To extract the Discharge relationship of Lopac gate in Submerged flow conditions, a control volume around the gate was considered and the relevant Momentum equation was written. Applying mathematical relations, theoretical Discharge equation for submerged condition was extracted. Based on dimensional analysis, the Discharge coefficient of Lopac gate in submerged conditions was a function of: the ratio of gate width (here equal to canal width) to upstream water depth (Bg/y1); the ratio of the gate opening to the gate width, which is called gate opening ratio (bg/Bg); submergence ratio; and the Reynolds and Froude numbers upstream of the gate (Re1, Fr1). The Reynolds number expresses the effect of viscosity forces. This factor plays a role only for large gate opening angles, where the upstream water depth decreases. According to the tests in the range of turbulent flow and for opening angles of 45 to 70 degrees, the impact of the viscosity force was negligible. Analysis of the results and affecting parameters on Discharge coefficient showed that for a constant gate opening with increasing submergence ratio, due to reduced secondary flow, upstream water depth increased, therefore the velocity head was reduced, which leaded to reduction of Discharge coefficient. By increasing the gate opening angle up to 52. 5 degree (opening ratio = 0. 39), Discharge coefficient had increasing trend at first and after that showed decreasing. For low gate openings, by increasing the gate opening angle up to 52. 5 degree, water depth was reduced, so velocity head was increased, leading to an increase of Cd. For higher gate opening angles of 52. 5 up to 70 degree (opening ratio =0. 66) the increased secondary flow dominated the relation and Cd was decreased. Therefore, the relationship of Cd with gate opening angle was increasing for the low angels, and decreasing for the high ones. Using experimental results and regression analysis of effective dimension-less parameters, an explicit and efficient relational for Discharge coefficient of Lopac gate for Submerged flow conditions, were estimated. The relation of the Discharge coefficient, considering three dimensionless parameters, was determined which provided high accuracy (with Root Mean Square Error of 0. 04, Mean Absolute Percentage Error of 4%, and Relative Error of 3. 6%). The Discharge coefficient equation under Submerged flow condition, as a function of two dimension-less parameters, the opening ratio (bg/Bg) and submerged ratio (y2/y1), was estimated as well. This relation provides similar accuracy as the main equation with Root Mean Square Error of 0. 042, Mean Absolute Percentage Error of 4. 6%, and Relative Error of 2. 59%. Therefore in terms of practical applications, this equation is recommended.

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APA: Copy

Yousofvand, f., MONEM, M.J., & KAVIANPOUR, M.R.. (2018). Estimating flow and discharge coefficient equations for Lopac gate in submerged condition. IRANIAN WATER RESEARCH JOURNAL, 12(2 (29) ), 51-58. SID. https://sid.ir/paper/159789/en

Vancouver: Copy

Yousofvand f., MONEM M.J., KAVIANPOUR M.R.. Estimating flow and discharge coefficient equations for Lopac gate in submerged condition. IRANIAN WATER RESEARCH JOURNAL[Internet]. 2018;12(2 (29) ):51-58. Available from: https://sid.ir/paper/159789/en

IEEE: Copy

f. Yousofvand, M.J. MONEM, and M.R. KAVIANPOUR, “Estimating flow and discharge coefficient equations for Lopac gate in submerged condition,” IRANIAN WATER RESEARCH JOURNAL, vol. 12, no. 2 (29) , pp. 51–58, 2018, [Online]. Available: https://sid.ir/paper/159789/en

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