Volume 19, Issue 1 (2019)                   MCEJ 2019, 19(1): 181-193 | Back to browse issues page

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Experimental Study of Flow Hydraulics in Ogee Spillways Affected by Converging Training Walls (case study: Germi Chay Dam). MCEJ 2019; 19 (1) :181-193
URL: http://mcej.modares.ac.ir/article-16-48885-en.html
Abstract:   (1086 Views)
The most typical kind of spillways is the ogee spillway. The advantages of the ogee spillway are its simple design, its steady overflow pattern, and the simplicity to pass flows, in comparison with the other spillways and the closely associated lower prices. In the present study, a 1:75 scale physical model was utilized to assess the impact of converging vertical training walls on the flow quantities in the ogee spillway. In this regard, this structure was tested in varying convergence of training walls ranging from 0 to 120°.  The experiments were conducted at the Soil Conservation and Watershed Management Research Institute (SCWMRI) in Tehran, Iran. The results of the experiments indicated that in the converging ogee spillway by increasing total upstream head, the discharge coefficient will go up for each of the convergence angles (θ’s) and before submergence stage for the spillway, the discharge coefficient is independent of converging situations. At a 0ᵒ convergence angle (with ratio of ), having free flow condition for each of the tested discharges, the highest ratio of relative discharge coefficients was 1.07. By contrast, at the submergence stage for the spillway, the difference in the discharge coefficient was observed noticeably. On the other hand, when the spillway was submerged, there is a decrease in the coefficient can be caused by tailwater submergence and it causes the differences in the discharge coefficient for each of the θ’s. For instance, the ratio of coefficient to the discharge coefficient (C/Cd) in 120° convergence, despite went up remarkably to just over 1.0 in H/Hd=1, the mentioned values then significantly dropped in H/Hd>1.8. Also, the data obtained from flow depth and static pressure distribution along the spillway in various convergence angles indicates that as θ increases, the flow depth and static pressure increases at the bottom and the toe of the spillway model. For instance, the flow depth along the convergence angle of 120 ̊ at station 4.3, was nearly 6.2 times greater than the flow depth generated along the 0 ̊ convergence. The range of flow depth changes with any increase in the total upstream head near the walls can be used to estimate the minimum side wall height requirements to decrease overtopping for future site utilizing similar design criteria. It can be inferred from experimental results that 60° convergence with ability to pass the probable maximum flood in the Maximum head allowed can be selected as the most economic convergence angle. This convergence angle was chosen because downstream channel width of it is 69% lesser than that in 0° convergence having capability to pass the probable maximum flood in the Maximum head. This study was aimed to evaluate the impact of converging training walls of the ogee spillway on flow characteristics. Experimental result showed that where the downstream flow is at supercritical stage or where the hydraulic jump occurs, the convergence angles variations has no effect on the discharge coefficient considerably, but when the spillway is submerged, there is a decrease in the coefficient which can be caused by tailwater submergence. In addition 60° convergence having the smallest downstream channel width required to pass the probable maximum flood in the Maximum head allowed can be selected as the most economic convergence angle.
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Article Type: Original Research | Subject: Earthquake
Received: 2021/01/3 | Accepted: 2019/05/15 | Published: 2019/05/15

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