Study Effect of Fluctuations of Pressure Factors of Stepped Short-throat Shaft Spillways on Hydraulic Coefficient

Document Type : Original Article


Department of Civil Engineering, Engineering Faculty, Islamic Azad University, Sepidan Branch, Sepidan, Iran.



Stepped spillways discharge more flow through themselves than smooth spillways theoretically. Therefore, understanding the flow behavior of these spillways can lead to better and more efficient use. In addition, the use of vortex breaker. can have a large impact on flow through the shaft spillway. For more efficient use, the risk of flow pressure dropping below the fluid vapor pressure, known as cavitation, should be prevented as much as possible. As for the spillways with stepped conduits (three steps), the pressure changes were found to be very tangible using a sextuple arrangement of vortex breakers for intermediate discharge rates; in some of the states, the pressure on the spillway's body is found to be intensely decreased. Based on the research, the best performance belongs to the morning glory-type spillway with 12 steps and three vortex breakers on the crest, as these accessories play an essential role in controlling the discharge rate and preventing cavitation. It is worth mentioning that the vortex breaker's dimensions based on the ratio of the vortex breaker's thickness (T) to the spillway's diameter (d) would not have an effect of more than 12.5% on the separation of the flow lines. In this study, an attempt was made to investigate the effect of different behaviors of the stepped chamber and different vortex shapes on the spillway flow. Based on the present experimental investigation, the following conclusions may be concluded:

Maximum risk of flow rate is magnitude at 1/3 down side of shaft.


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