Hydraulic Type-A Piano Key Weirs with Zigzag Lateral Crest

Document Type : پژوهشی

Authors

• sobhan moradi ¹
• hamed shahsavary ¹
• atefe arfa ²
• kazem esmaili ¹

¹ Department of Water Engineering, Ferdowsi University of Mashhad, Iran

² Department of Water Engineering, Tarbiat Modares University of Tehran, Iran

10.22067/civil.v1i33.71041

Abstract

According to the literature, increased velocity approaching has been reported as the most important factor in decreasing discharge capacity in piano key weirs. In the present study, first, by applying variable water head, changes in the discharge coefficient of standard piano key weir (type A) were investigated, then by presenting a new design of zigzag form in lateral crest profile, hydraulic flow parameters upstream of weir by ADV velocimeter The measurements were performed and analyzed by Buckingham method. The results showed that by zigzagging the lateral crest profile of the piano key weirs, the maximum discharge coefficient occurs at a lower ratio but with a higher numerical value, as the average discharge coefficient increasing by 10%. Increases by 22 and 16 percent, respectively, for transverse and upward velocities of flow in the crest elevation range, reinforcing secondary upstream currents. Hence, by incorporating a more effective length of the lateral crest, it increases the deflection and suction current to the outlet keys than the standard crest. Therefore, with the increase in energy loss (increase in water level drop in range (B)), an 11% decrease in the values ​​of the approaching component velocity occurred at the inlet keys. Also, the intensity values ​​of turbulence with zigzagging of the lateral crest profile were, on average, 15% higher than the standard piano key weir form. Finally, the proposed crest form increases the local submergence limit and improves the discharge transfer efficiency of the A-type key piano weir outlet keys.

Keywords

• Congress crest
• Discharge coefficient
• Flow velocity
• Piano key overflow
• Submerged stream

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