Investigation of Elbow Radius Effect on Formation of Cavitation in Morning Glory Spillway

Morning glory spillway is one of the most susceptible cases for the occurrence of the cavitation phenomena. In the present study, the flow characteristics included the inlet and outlet discharge and the velocity and pressure close to the elbow walls were calculated for Alborz dam spillway by using of Flow3D software and the results were compared with the experimental data. The comparison of the numerical model results and the experimental data showed the good agreement between them. The results showed, the maximum pressure head in different discharges and for different elbow radius, have been located in median of piezometer in the bottem of elbow. As a result, it is suggested that, if possible, the curvature changes in the entrance area from the vertical shaft to the elbow and also from the elbow to the horizontal tunnel gradually. In different discharge and different radius of the elbow, the cavitation index for bottem of the elbow will increase as a result of dynamic impacts on the bottem of the elbow, but the cavitation index, toward to the end of the curvature, will be lower due to the contraction end of the cross section. The results showed that radius change of the elbow due to considerable effect on the flow field, has the significant effect on the occurrence probability of the cavitation. The radius change of the elbow has the different results for the submerged flow and free surface regimes.