Experimental Investigation of the Wedge-Shaped Deflector Installation Position Effects on the Flip Bucket Spillway Energy Dissipation

introduction
A spillway is a very important structure usually used to provide the controlled release of water from a dam or
sometimes levee downstream, typically into the riverbed of the dammed river itself. Spillways ensure that water does not destroy parts of the structures not designed to convey water. many Energy-dissipating structures (such as ., hydraulic jump stilling basins, roller buckets, ski jump buckets) are usually located at the end of spillways discharge channels in order to dissipate the extra energy which comes from the water . Specifically, flip buckets are mainly placed at the end of f high dams in order to dissipate the energy with high-velocity flows . having said that these structures ( Flip buckets) are used when velocity of the water is larger than about 15-20 m/s.
Energy dissipation controlling has always been one of the most significant and vital matter and concern of hydraulic scientists and researchers especially in tall dams. one of the most common method to dissipate energy is to discharge flow away from hydraulic structures and downstream by using Flip bucket spill way .The sky-jump spillway is an economical and effective solution to return water to a river . many years ago in the past various models of flip bucket spillways , like simple, splitter, and deflector, and so on have been built,
but information about the ways of increasing energy dissipation and controlling the bad effects of the extra energy of the water are still limited and more studies are needed .
in order to increase the efficiency of this dissipater structure some wedge shape deflectors were designed to decrease the effect of this destructive energy on down stream.in this regard the effect of deflector installation position on energy dissipation was experimentally investigated. The main result indicate that the increase of linear distance of deflectors from the bucket remarkably result in an increase in energy dissipation and a decrease in jet length..

Methodology
To investigate the effect of deflector installation position on energy dissipation and the length of the jet a new experimental study was conducted in the Hydraulic laboratory of Shahid Chamran university of Ahvaz.
3 wedged-shape structures with Hight of 10 cm ,,length of 6 cm and angle of 47 degree were made .40 experiments were performed at 4 different linear distance from the edge of the bucket and one deflector-free experiment was carried out as a compression to other experiments. It is worth mentioning that all experiments including deflector-free one ,were performed at 8 dimensionless parameter Yc/H . At each experiment the linear distance from the edge of bucket was increased and the depth of tailwater was read .In the end relative energy dissipation was concluded by measuring the total energy in the upstream and downstream. in addition to the energy dissipation , Jet length ( for each experiment )was determined by using Get data software and the photos taken during the study .

Results and discussion
In general Data analysis demonstrated that the waged-shape structures resulted in a remarkable increase in the amount of energy dissipation and a major decrease in jet length ,due to the increase of water and air mixture compare to the deflector - free experiments .Indeed deflectors divide the incoming jet to two small different jets ,therefore the combination of these two small jets leads to the increase in water and air mixture and consequently the increase of relative energy dissipation .Moreover it has been shown that the energy dissipation increased by increasing the linear distance from the bucket. Furthermore the experimental study on jet length indicated a remarkable decrease in the jet length by the increasing of the linear distance.in other words the different installation position of deflector increase the Hight of jet trajectory .it directly increases the contact surface of jet and air and leads to increase of energy dissipation and consequently decrease of jet length.

Conclusion
In general the increase of linear distance from the edge of bucket ( in flip bucket spillway ) resulted in the increase in energy dissipation and the decrease in jet length .Maximum observed relative energy dissipation was 65.87 which occurred in the Yc/H = 0.027 and Lx/L = 7.3 and minimum observed relative energy dissipation was 57.54 ,which occurred in the Yc/H = 0.061 and Lx/L = 4.3. furthermore maximum observed jet length was105 cm, which occurred in Yc/H = 0.061 and its minimum was 35 cm, which occurred in Yc/H = 0.027. therefor according to the results of the all experiments using deflector in different possessions as a new way of controlling and increasing energy dissipation is highly recommended .