Author(s): Kyung-Su Lee; Chang-Lae Jang; Nam-Joo Lee; Sang-Jin Ahn; Jae-Kwang Jung
Linked Author(s): Chang-Lae Jang
Keywords: Movable weir; Discharge coefficient; Relative crest length; Rating curve
Abstract: This study investigates the discharge coefficient of a pneumatic operation weir, a kind of movable weirs, to estimate much more accurate rating curves using laboratory flume experiments. The improved pneumatic operation weirs are constructed to prevent water pollution from sedimentation of organic matter. The channel is 12 m in length, 0.6 m in width and 0.5 m in height with variable slope. Several bed slopes and flow conditions are considered. The bed slopes are considered in 1/1000,1/750 and 1/500. The rising angles of the weir are 30,40,50, and 60 degree under flow conditions. The equations of rating curves related to flows under control of the angles of weir at each bed slope are estimated. The discharge coefficient (Cd) is from 0.61 to 0.75 by the stand-up angle of the weir. The dimensionless parameters affected by upstream flow is the ratio of the flow head to weir height (H1/W), Froude number upstream (Fr1), the ratio of critical depth to water depth upstream (yc/y1). The dimensionless variables affected by flow downstream is the relative depth downstream, which is the difference water depth between up and downstream to water depth downstream (△y/y 2), Froude number downstream (Fr2) and the relative crest length (ξ). As the yc, ξ, Fr 1, △y/y 2, yc/y 1 and H 1 /W increases, the discharge coefficient (C d) increases. As the△y/y 2 increase, the Fr 1 and Fr 2 increase while the C d and△y/y 2 decrease. Free flow is observed at the range of 0.03 1 /W≤0.3 and the submerged flow is at the range of 0.76 1 /W≤1.9. C d decreases as H 1 decreases in condition of constant W. However, Cd increases as the L/W increases.
Year: 2014