B. Khatamipour - Science and research Branch, Islamic Azad University, Tehran, Iran
A. Khosrojerdi - Science and research Branch, Islamic Azad University, Tehran, Iran
M. R. Kavianpour - KN Toosi University of Technology, ۴۷۰ Mirdamad Ave. west, Tehran, Iran
M. Ghodsi Hassanabad - Science and research Branch, Islamic Azad University, Tehran, Iran

Pivot weirs are one of the most important structures for regulating the water level in rivers and canals. These weirs are constructed with one or more gates in a row in the waterways. Changing the angle of each gate is done individually with an independent system. Based on available information, the hydraulic performance of this type of weirs (especially in several gates and different angles) in different operational conditions has not been investigated. In present study, pivot weirs with two gates are simulated using Ansys CFX software with the angles of ۲۷.۸ to ۹۰ degree and the discharges between ۴۰ to ۱۳۰ L/s. Further, the importance of the open space between the two adjacent weirs with different angles (lack of retail wall) and its hydraulic behavior have been studied. The model was calibrated based on valid laboratory data and using the K-ϵ turbulence model.  Therefore, the weirs with equal angles were studied in the first step. In this case, the effective discharge angle coefficient was studied and its maximum value compared to the vertical angle was obtained ۱.۰۷۶ for the angle of ۵۲°. Furthermore, relationships for discharge coefficient versus upstream water depth were developed. In the next step, the effective length of the crest was found to be increases by ۳۰% under unequal angles operation and the discharge coefficient raised by ۱.۳ to ۲.۴ times. Also, it was recognized that, in case of two weirs with unequal angles, about ۲۶% to ۶۹% of the flow passes through the distance between the two weirs. Therefore, the performance of unequal angles operation seems to be more effective in controlling the water level and discharge in different conditions and especially in flood events.

Ansys CFX, Pivot Weir, k-ε turbulence model, Discharge coefficient, Free flow