hamzeh ebrahimnezhadian - Ph.D. Candidate in Water & Hydraulic Structures, Dept. of Civil Eng., Faculty of Eng., Urmia University, Urmia, Iran.
mir ali mohammadi - Associate Prof. in Civil Eng., Water & Hydraulic Structures, Dept. of Civil Eng., Faculty of Eng., Urmia University, Urmia, Iran
ramin abdullah kookhi - Ph.D. Candidate in Water & Hydraulic Structures, Dept. of Civil Eng., Faculty of Eng., Islamic Azad University, Arak, Iran.
ako seyedi - MSc in Civil Engineering-Water, Islamic Azad University, Maragheh, Iran.

Water has high velocity passing through spillways or bottom channels of dams. Under this condition, it would have a great deal of kinetic energy; therefore, energy dissipater structures must be used in order to dissipate such destructive energies. Analyzing the flow passing through spillways is typically done by analytical relations and physical models. However, nowadays thanks to advances in computer sciences, using numerical models has grown noticeably, because of using less time and cost compared to physical models. In this study, flow characteristics, including pressure distribution and average flow velocity, were studied in different points of flood evacuation system, and were compared with the results of physical model. Then, using the results of pressure and velocity, potential occurrence of destructive cavitation was studied on chute of spillway. The results indicated acceptable compatibility between the results of numerical model and those of experimental model; therefore, it can be argued that this software has an acceptable ability in simulating free surface flows, particularly in velocity and pressure field. RNG K- 8 turbulence model, among other turbulence models, has the highest compatibility in simulating flow characteristics. The study of results showed that at a certain span in the length of spillway, cavitation index is set lower than the critical point, and the occurrence of cavitation is strengthened from this point onwards and the risk of cavitation occurrence increases. This necessitates the use of aeration equipment in such areas in order to prevent the occurrence of cavitation.

Ogee spillway, velocity and pressure distribution, cavitation indicator, Flow-3D software