Abstract
Bottom outlets are significant structures of dams, which are responsible for controlling the flow rate, operation, or removal of reservoir sedimentation. The service gate controls the outlet flow rate, and whenever this gate is out of order, the emergency gate which is located at upstream is utilized. The cavitation phenomenon is one of the common bottom outlets’ problems due to the rapid flow transfer. The present research is a numerical study of the flow pattern in a dam’s bottom outlet for different gate openings by the use of Flow-3D software and RNG k-ε turbulence model. The investigation is carried out on the Sardab Dam, an earth dam in Isfahan (Iran). The maximum velocity for 100% opening of the gate and Howell Bunger valve is about 18 m/s in the section below the gate, and the maximum velocity for 40% opening of the gate is equal to 23.1 m/s. For 50% opening of the service and emergency gate in the valve’s upstream areas, the desired pressure values are reduced. Moreover, in the areas between the two emergency and service gates, the pressure values are reduced. The possibility of cavitation in this area can be reduced by installing aerators. The flow pattern in Sardab Dam’s bottom outlet has relatively stable and proper conditions, and there are no troublesome hydraulic phenomena such as local vortices, undesirable variations in pressure, and velocity in the tunnel, and there is no flow separation in the critical area of flow entering into the branch.
Highlights
Bottom outlets are utilized as one of the dam’s hydraulic structures to control the reservoir impoundment, the reservoir evacuation in case of emergency, and the removal of the sediments entering the reservoir
By studying failure causes of dams’ terminal gates, it has been determined that the cavitation phenomenon and gate vibration are the chief reasons for damages, because, in the areas where air bubbles collapse, pressure fluctuations intensity raises [3,4,5,6,7,8]
In order to evaluate the numerical model results’ calibration and validation in various bottom outlet’s gate openings, the output flow rate of the manual analysis should be compared with the output flow rate of the numerical model for the same applied head conditions using the analytical solution performed in the previous sections
Summary
Bottom outlets are utilized as one of the dam’s hydraulic structures to control the reservoir impoundment, the reservoir evacuation in case of emergency, and the removal of the sediments entering the reservoir. They require careful design and harmful factors identification [1]. By studying failure causes of dams’ terminal gates, it has been determined that the cavitation phenomenon and gate vibration are the chief reasons for damages, because, in the areas where air bubbles collapse, pressure fluctuations intensity raises [3,4,5,6,7,8]. Aeration by aerator tube is usually employed in order to control this phenomenon [9,10,11,12]
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