Experimental Study of Pyramid Vortex Breakers Effect on the Discharge Coefficient of Submerged Morning Glory Spillway

Abstract

Morning glory spillway is built upstream of the dam in the reservoir to convey water from the reservoir to the downstream. The main problem of the spillway is the swirling flow and vortex around the spillway’s axis. By increasing the submergence height, the vortex will increase which leads to the reduction of flood conveyance efficiency due to a decrease in the discharge coefficient of the spillway. It is well known that the vortex breakers are the best for increasing the discharge coefficient of the morning glory spillway. In the present article, a physical model of morning glory spillway is designed and constructed to study the effect of the number and characteristics of pyramidal vortex breakers on the discharge coefficient of the spillway. 209 experiments have been conducted in the Hydraulic Laboratory of SRBIAU, Tehran. Applying non-linear regression analyses, empirical equations were obtained for estimating the discharge coefficient of morning glory spillway with pyramidal vortex breakers. Through comparison of results of the new equations and observed data, the determination coefficients of training and testing data for triangular and square pyramidal vortex breakers was calculated as 0.99 and 0.926, respectively. Also, sensitivity analysis is performed to investigate the efficient variables on the discharge coefficient of morning glory spillway with pyramidal vortex breakers. Findings show that pyramidal vortex breakers in a group of six increase the discharge coefficient significantly. The discharge coefficient performance due to pyramidal vortex breakers existence increases by 11.80% up to 16.13% compared to the non vortex breaker morning glory spillway.