Assessment of the Destruction Causes at the Downstream Basins of Mill-Mugan Dam Using Computational Fluid Dynamics

In this research 3D hydrodynamics of Mill-Mugan diversion dam at a domain with a length of 500 meters was simulated numerically using large eddy simulation (LES) method. All of the components of the dam such as radial gates and stilling basin were considered and the causes of destruction occurrence at the downstream basins were investigated under various operating conditions. Simulated stage-discharge curve of a single radial gate was compared with data reported by dam consultant and also with relationships available in the literature, which confirms the validation of the numerical model. Furthermore, flow patterns of the numerical model were compared with images taken from the study area. Study domain were discretized using 25 million cells. Numerical simulation was performed using parallel processing and to provide the steady state condition, simulation was continued for up to 1000 seconds. Results showed that in all scenarios of the symmetric operating condition, hydraulic jump downstream of the radial gates formed inside the main stilling basin. However, the high end sill caused hydraulic obstruction and as the subcritical flow passed over the sill, critical flow formed at its top followed by a supercritical flow thereafter. Consequently, another hydraulic jump occurred when flow reached the subcritical flow in the protection trench, located downstream of the main stilling basin. Due to the diverging geometry of the side walls, a radial hydraulic jump occurred further downstream. Hydraulic jumps exert strong dynamic loads to the flexible concrete blocks inside the protection trench and it causes rupture of the chains connecting the concrete blocks. Under asymmetric operating conditions of the radial gates, hydraulic jump is swept out of the main stilling basin and it exacerbates unfavorable hydraulic conditions downstream of the dam.