Hydraulic analysis and cavitation phenomenon in physical and numerical models of the bottom outlet in Rudbar dam, Lorestan province, Iran.

Sattar Khazaei, Reza Ellahi, Ehsan Niknami, Kurush Shahverdi

Monday 29 june 2015

16:00 - 16:15h at North America (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 3I. Engineering - Industrial

Bottom outlets are one of the main components in dams that are prone to numerous hydraulic problems such as variations in pressure that can affect the structure’s performance if not controlled. Rudbar Dam in Lorestan with a height of 158 meters is one of the highest earth dams under construction in Iran. In operation, this dam uses a bottom outlet for flood discharge and for controlling the water level in the reservoir. Due to the fact that upstream pressure head the discharge tunnel and the control gate is so high at all times (Normal head is 127.2m), the flow in the tunnel is under pressure and past the control gate it becomes a free surface flow, which after colliding with the tunnel’s floor creates a wing shaped flow moved towards the ceiling of the tunnel in a distance of 37 to 42 meters from the gate. This phenomenon can suffocate this section of tunnel and by creating dynamic pressures leads to wearing and destruction of the tunnel’s ceiling. Eventually by increasing the flow rate required for the upstream of aeration system, destroys the gates. Because of the problems observed in the preliminary physical model of the bottom outlet, the outlet was designed using computational fluid dynamics (CFD) and the flow was simulated with numerical models using Flow 3D and ANSYS (Fluent) software products to eliminate the problem and to avoid redoing the physical modeling of the outlet and to also limit the variations in it as much as possible. Using the numerical model, it was observed in early stages of the study that past the gate, flow has a similar consistency with the ones obtained from it. After calibrating the numerical model with the initial results of the physical model, with several changes were applied to the geometry of downstream tunnel and analyzed in both numerical models (Fluent, Flow 3D), has been trying to improve it. It also analyzed the phenomenon of cavitation and takes the necessary steps to prevent it in bottom outlets.