Experimental Study the Effect of Blades Thickness in the Combined Structure of Ogee Spillway - Lower Bypass on Energy Loss and Downstream Hydraulic Jump Characteristics

In this research the effects of installed blades on the combined model of ogee spillway with lower bypass on energy loss of structure and downstream hydraulic jump characteristics has been experimentally investigated. In order to achieve the goal of this study, a physical model of ogee spillway with lower bypass was built, in which the output jet from the lower bypass (bottom outlet) was set to be at the angle of 30 degrees to the overflow of spillway. Installation of blades at the upstream of the lower bypass slit makes flow separation and more turbulence on spillway and as a result more energy dissipation on structure. In this research, two blades relative thickness including tb/ y1d= 0.07 and 0.14 were used and the results showed that the blades with the higher relative thickness (i.e. tb/ y1d=0.14) was found to be more effective in energy dissipation on structure and less values for the downstream hydraulic jump parameters. The measured values showed that the average energy loss on spillway, and the reduction length and secondary relative depth of hydraulic jump were 47.6%, 40% and 23.2%, respectively. According to the results obtained in this research study, the use of this structure is recommended for economical stilling basin construction at the downstream of small dams and spillways.