The effect of energy dissipation due to outflow water jet from floor and end of stilling basin on hydraulic jump

Introduction
The purpose of controlling hydraulic jump order to prevent damages caused by energy water in supercritical speeds of the research. To control the hydraulic jump and to prevent damage caused by water energy at supercritical speeds, at the end of structures such as spillways, special structures called energy dissipation are used which are built downstream. A further part of the research carried out by various researchers is expressed. Results show that the rough bed in comparison with the smooth bed, will decrease the jump relative depth in an average of 56.7 percent and the relative energy dissipation increases 69 percent and the shear modulus increases 2.6 percent. The goal of this study is reducing the hydraulic jump ̓s length to prevent the damage caused by the energy of water and reducing the length of the stilling basin, in the supercritical flow that passing the spillways.
Materials and Methods
The experiments had performed in a flume with a width of 0.3 m, a length of 10 m, its height that was 0.75 m at first 2.5 m of the flume and 0.45 m in its remaining flume length, and zero slopes in the hydraulic laboratory of Behbahan Khatam Al-Anbia University of Technology. In all experiments, hydraulic characteristics including jump length, rolling length, crossing discharge from the spillway, crossing discharge from the jet, second depth, tail water depth, water depth the back of the spillway, water height on the spillway, spillway water head recorded. The flow depth measured depth gauge with an accuracy of 0.1 mm at three fixed points and their average. In this research in order to determine the best model of energy dissipation and economization of the stilling basin with smaller dimensions for modeling the using several methods such as creating a slot in the spillway-body, on the floor of the stilling basin, and end of the stilling basin. In total 65 experiments with a Froude number of 4.56 to 10.18 were performed. In all experiments, the cross-section of the slot (jet) was constant and discharge was 16,12,8 L/s.

Results and Conclusions
Four series of experiments with different landings were performed to determine the evaluation of different models to reduce the length of the hydraulic jump and select the best model. The first stage test (control test) will be used using a without jet spillway to determine the jet flow rate and compare the jump length with other models. The results of these experiments, similar to previous studies, show that with increasing discharge spillway, the Froude number decreases, and the length of the jump and the length of the roll increase. The experiment of the second series (slot in the body of the spillway) By creating a slot with an angle of 45 degrees in the body of the spillway, we came to the conclusion that the slot in the body of the spillway was able to reduce the jump length between 14.28 to 4.76 percent in different flows. Third stage experiment (slot in the floor) Comparison of the results of the tests of the effect of the slot in the floor spillway with the control experiments showed that the use of the slot in the floor of the spillway at all distances reduced the hydraulic jump length compared to the control experiments at similar discharges. Also, the effect of using a slot in the floor on reducing the length of the hydraulic jump has increased as the slot approaches the spillway. The best way to reduce the jump length is related to the slot attached to the spillway, which has reduced the jump length by 59 to 67% for different discharges of the spillway compared to without a jet mode. Third Stage Experiment (slot in floor) Comparison of the results of the stilling basin floor impact tests the free experiments showed that the use of the stilling basin floor slot at all distances reduced the hydraulic jump length compared to the free experiments at similar discharges. Also, the effect of using the slot in the floor on reducing the length of the hydraulic jump has increased with the slot approaching the spillway, so that the best way to reduce the jump length is related to the gap attached to the overflow, which is 59 to 67% for different discharges without jet reduced. Fourth Stage Experiment ( the jet at the end ) The jet at the end of the stilling basin at all distances experiments showed that the jet at the jump was submerged because the momentum caused by the discharge passing through the flow over the spillway caused it to push water. The spillway water a submerged jump mode has been created the jump energy has been depleted. The experiments showed all discharge inflow tested, the closer the jet is to the spillway, the best jump length. The best mode was to reduce the jump length of the jet attached to the spillway, which reduces the jump length by 80 to 88% in different discharges to the spillway compared to without a jet mode.
Conclusion: In these experiments, by examining the effect of the jet on different models, the results showed that using the jet at the end of the stilling basin at different distances and discharges has a better performance compared to other models. The jet at the end in the stilling basin had a jump length of maximum discharge 88% reduction, the slot jump length in the floor of the stilling basin 67.42% reduction and finally the slot jump length in the spillway body 14.28% reduction, which has the lowest reduction in jump length compared to other models of this research .In this study, the jet at the end of the stilling basin in different discharges reduces the level of the upstream water level, which in the maximum flow was able to reduce the upstream water level by 5.67%.