Experimental Investigation of the Effect of Sidewall Slope on Discharge Coefficient the Trapezoidal Piano Key Weir and Comparison with Rectangular

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Experimental Investigation of the Effect of Sidewall Slope on Discharge Coefficient the Trapezoidal Piano Key Weir and Comparison with Rectangular

ارائه دهنده: Provider: Ali Gholami

اساتید راهنما: Supervisors: Dr. Morteza Shokri

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Bahram Rezaei - Dr. Jalal Akbari

زمان و تاریخ ارائه: Time and date of presentation: 22024

مکان ارائه: Place of presentation: 43

چکیده: Abstract: The Piano Key Weir (PKW) is one of the most recent nonlinear weirs, offering a longer crest length compared to linear sharp-crested weirs. It has emerged as a suitable option for increasing the safety factor of dams, enhancing the discharge capacity of existing or under-construction dam spillways, and augmenting flood storage in a cost-effective and reliable manner compared to other types of weirs. Research indicates that with increased water head on PKWs, the discharge efficiency decreases due to flow submergence at the inlet keys of the weir. According to ICOLD reports, one-third of dam failures are attributed to inadequate spillway design, highlighting the importance of developing appropriate weirs to prevent catastrophic failures. In this study, a novel solution is explored to enhance the discharge capacity of PKWs by modifying the sidewall slopes. The objective is to improve the performance of the PKW during flood events while also maximizing water storage upstream under non-critical conditions. To achieve this, experiments were conducted on two PKW models—rectangular and trapezoidal—with sidewall slopes of 0°, 5°, 7.5°, and 10° under nine different flow rates. The weirs were inclined both in the flow direction (positive slope) and against the flow direction (negative slope), resulting in a total of 126 experimental runs, and all laboratory observations were recorded. The results demonstrate that rectangular and trapezoidal PKWs with negative slopes (against the flow direction) exhibit higher discharge capacities than non-sloped PKWs, particularly when more than 75% of the weir crest length is involved in flow discharge. Additionally, the findings show that the discharge coefficient of the rectangular PKW with a 5° negative slope is, on average, 6% higher than that of the non-sloped rectangular PKW, and the discharge coefficient of the trapezoidal PKW with a 5° negative slope is, on average, 7% higher than that of the non-sloped trapezoidal PKW. These results indicate that sloped PKWs can significantly improve flood management and water storage efficiency. For all tested models, the effective crest length, discharge coefficient, spillway performance, and flow profiles were examined, and an empirical equation to estimate the discharge coefficient of PKWs was proposed.

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