Document Type : Original Article
Authors
1
Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
2
Ph.d Student of Water Structures., Department of Hydraulic Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
3
Professor, Department of Hydraulic Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
4
Ph.d Student of Water Structures, Department of Hydraulic Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
Abstract
The low inflow rate of water into the dam reservoirs causes sedimentation, leading to a decrease in the service life of dam. As a result, the performance of the dam in controlling floods and generating energy through water release downstream will be affected. Additionally, sediment deposition near the bottom outlets and turbines causes their burial, leading to difficulties in their operation and utilization. Installing inclined plates in the upper of bottom outlets is suggested as a new method to increase the amount of flushed sediments in pressurized flushing. Awareness of changes in the upstream flow pattern of the orifice is of great importance. In the present study, the effect of installing inclined plates on flow pattern changes in the upstream of the orifice was investigated using the Flow3D model.
In this study, a numerical model calibration was performed using the results of experiments conducted in the hydraulic laboratory of the Faculty of Water and Environmental Engineering at Shahid Chamran University of Ahvaz, and the RNG turbulence model was chosen for conducting the simulation. The considered variables include plate width, plate installation angle, and plate installation distance to the orifice. In total, 5 scenarios (including the reference test (i.e., without installing plates)) have been defined for the numerical model.
The results showed that the installation of inclined plates against the orifice led to the creation of vortexes and the development of a low-pressure zone, resulting in an increase in the volume of flushed sediment. Also, reducing the width of plates, increasing the installation angle, and increasing the installation distance of the plates will lead to a decrease in the intensity of eddies and a decrease in the range of low-pressure zone, which reduces the effect of installing inclined plates to increase flushed sediment volume.
Based on previous studies, the amount of sediment output in pressurized flushing is limited and confined to the vicinity of the dam body. Therefore, this method is not used to revive the dead storage capacity of the dam reservoirs. Ancillary facilities such as bottom outlets and hydro-power plant outlets are located near the dam structure, and sediment entry into these facilities can have destructive effects. Therefore, providing methods to increase sediment discharge from near the dam body can be highly beneficial. Additionally, by creating a low-pressure zone in the upstream of the outlet, a suction effect is created, which can be useful in increasing the volume of sediment discharged during turbidity current discharging from the bottom outlet.
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