triangular overflow

One of the erosion control options in the downstream of the overflows is to use crushed stone to reduce the excess output energy and to minimize the amount of erosion and scouring in the downstream of the overflow. In this research, experiments were conducted to check the stability of the rock in the downstream of the spillway by changing the threshold angle. For this purpose, a triangular cup overflow with four different threshold angles was made of fiberglass. Experiments were carried out using a piled stone density with four different diameters in clear water. In each experiment, the flow depth was measured under the movement threshold conditions and then the stability number was calculated using the obtained data. The results of this research showed that the highest stability number related to the overflow with a threshold of 45 degrees and the lowest stability number was observed in the overflow with a threshold of 15 degrees. Also, the relative diameter of the aggregates is also an effective factor in the stability of the aggregates, and the stability number at the threshold of movement in the four angles of the triangular overflow threshold decreases with the increase of the relative diameter of the aggregates. In order to provide a relationship to estimate the relative diameter of the checkered stone, the variables of the investigation and the correlation coefficient of the results obtained from this relationship with the laboratory results for the triangular overflow were obtained as 0.85.

In this study, experiments were performed to investigate the relative energy losses in two models of simple triangular and toothed overflow made of fiberglass in four different landings at three depths of 100%, 90%, and 80%. The effective variables in this study were the landing number and the bottom depth at the end of the hydraulic jump. The results of this study showed that at three downstream depths, energy losses decrease with increasing landing number. Also, energy losses in the free projectile mode are higher than in the other two modes due to the full development of the hydraulic jump. In the general comparison mode, the performance of a toothed triangular overflow is better in energy dissipation than in the toothed mode, due to the fracture and compression of the flow lines in contact with the teeth at the end of the overflow projectile. In general, the use of teeth at the end of the overflow projectile causes energy loss in the conditions of 100% of the bottom depth in the toothed triangular overflow compared to the simple triangular overflow by an average of 7%, and in the conditions of 90% and 80% of the bottom depth by about 8% and 10%, respectively.