Numerical simulation of gate angle effect on flow and its interaction with downstream erodible bed

Stability of hydraulic structures is one of the main problem that usually researchers focused on it. Bed change around the hydraulic structures caused by flow is one of this effected items on stability. In this research, the scouring and sedimentation downstream of gate with different angles (30, 45, 60 and 75 degrees) has been investigated with Flow-3D software. This simulation results illustrated that Flow-3D software in addition to the prediction of scour depth and sedimentation high with R2=0.9, have acceptable results of bed shape change in simulation. The erodible bed changes showed that with increasing of angle up to 45 degrees, scour depth will increase up to 3.4 times of flow jet thickness, while for gate with 60 degrees this amount is minimum and equal to 2.8. Distance of scour and sedimentation maximum depth and high for 60 degrees was about 12 times of flow jet thickness, also wide and length of composed vortex downstream of gate were about equal to flow depth and 16 to 17 times of flow jet thickness, respectively. The vortex circulation between separation stream layer and gate, and its velocity is 10 percent of jet velocity which rotate counter clockwise. So gate with angle of 60 degrees according to scour depth and sedimentation high was the best angle for design.