Experimental Study on the Effect of Geometry and Upstream Channel Bed Level on Discharge Coefficient of Trapezoidal Labyrinth Weir

Document Type : Research Article

Author

Abstract

Labyrinth weirs are one of the most common structures in regulating water level and release of flow in irrigation channels and reservoirs of the dams without special operation. A major problem in the operation of these structures in water conveyance channels is sedimentation at the upstream of the weirs, which can affect the performance of these structures. In this research, the effects of changes in the geometry and upstream channel bed of weirs on the discharge coefficient of the trapezoidal labyrinth weirs was investigated experimentally. Experiments were performed for cases without change in channel bed level and 3 levels of channel bed changes at the upstream of weirs (30, 60 and 90 percent of weir height), and six geometries of trapezoidal labyrinth weirs under wide range of flow discharges. The experimental results showed that increase of the channel bed level up to 60 percent of the weir height did not affect discharge coefficients of the labyrinth weirs. However, by increasing the channel bed level to 90 percent of weir height, there was a decrease of approximately 14 percent in discharge coefficients of the weirs with respect to the case with no changes in channel bed level. The comparison of results indicated that because of increase in local submergence at the outlet cycles of the weirs, for upstream channel bed level smaller than 90% of the weir height, the discharge coefficients of the trapezoidal labyrinth weirs with smaller angle of apex cycles and larger length of cycles in flow direction was more than other geometries of the weirs. By increasing the upstream channel bed level to 90 percent of the weir height, the approaching flow velocity increases and most parts of flow, releases from apex of the cycles since it requires larger momentum to exit from the cycles. Therefore, for discharge coefficient of the labyrinth weirs with larger angle of apex, both the cycles and smaller length of the cycles in flow direction were more effective than other geometries. 

Keywords


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  • Receive Date: 22 December 2015
  • Revise Date: 14 October 2016
  • Accept Date: 29 November 2016
  • First Publish Date: 29 November 2016