Investigation of Scour Mechanism Due to Simultaneous Operations of Submerged Wall and Impinging Jets Using Flow3D Model

High kinetic energy of supercritical flow formed from spillways as well as middle and bottom outlets of the dam body are commonly considered a water jet. This flow type in interaction with the erodible bed can endanger the stability of structures located in its path. The main purpose of this study is to assess the mechanisms of flow and scour due to simultaneous operations of wall and impinging jets. To this end, the flow pattern and the scouring process has been simulated by Flow3D. First, the numerical model results are validated against experimental data. Then the velocity vectors, secondary currents due to the collision of water jets, and the geometric parameters of scour (e.g., scour depth, scour length, and ridge height) are investigated at various stages from the beginning of the scouring process to the equilibrium. The results of the flow pattern analysis indicated that by the collision of water jets, a single clockwise rotating vortex is formed at intersection of the jets. The latter vortex leads to further erosion of a sediment bed. Flow separation occurs at the top of the ridge due to the accumulation of the eroded sediments at the downstream of the scour hole over time. A counter-clockwise vortex is generated at the upstream of the ridge as a result of the flow separation. Investigation of the scour mechanism demonstrated that the highest scouring propagation rate occurs during the early stages of the scouring process.