Experimental Investigation of Energy Loss in Crump Spillways in Free Flow and Submerged State

Dams are one of the best ways to store water in the long term. In general, it is important to increase the coefficient of water passage, more energy loss, and of course, to reduce scour downstream of dams and hydraulic structures and overflows. Weirs are part of hydraulic structures that allow more flow to pass over them during floods. Crump spillway also improves and protects the body of dams and spillway by passing excess flow during floods. Increasing the energy loss prevents the flow rate and scour or reduces the scour and prevents cracking and overturning of the crump weir. Many people have done valuable studies on the water transfer coefficient of crump weirs, but a review of previous research shows that few researchers have investigated the energy dissipation of crump weirs. Also, the energy dissipation in free flow and submerged states in Crump weirs has not been investigated. One of the conditions that can lead to an increase in energy loss is the presence of obstacles in the downstream slope of crump spillways. To better understand these cases, in this research, Crump spillways with different heights and slopes upstream and downstream were used. Also, the existence of the block (baffle) and the free and immersed states of the flow were investigated to estimate the energy losses. Experiments were carried out in a flume 10 meters long, 0.6 meters wide and 1.2 meters high. The flow is supplied by a pool tank and a pump. The flow is calmed down by flow relaxers and then reaches the overflow in 6 meters. To evaluate the effect of the slope and height of the spillway, three spillway models with a height of 0.15 meters and one spillway with a height of 0.2 meters and with different slopes upstream and downstream of the spillway were used. The flow rates used are 0.03, 0.035, 0.04, 0.045 and 0.05 cubic meters per second. By setting the appropriate engine speed for the pump, the flow rate entered the laboratory flume through the tank and the water depth was measured with the sensors installed on the top of the flume. The results showed that with the increase in the height of the overflows, the amount of energy loss decreases. The amount of energy loss in free flow mode with baffle is higher than the amount of energy loss in free flow mode without baffle. The amount of energy loss in submerged flow mode is lower than the amount of energy loss in free flow mode. As the downstream angle of the overflow decreases, the energy loss increases. By reducing the upstream angle of the overflow, energy loss is reduced. The amount of energy loss in free flow mode in type A, B, C and D spillways is 33.29, 33.83, 39.77 and 27.32% respectively. A general relationship was presented to calculate the amount of energy loss in crump weirs. In this relationship, there is a coefficient that is a function of free flow without baffle, submerged flow and free flow with baffle.