Numerical Simulation of Flow in Piano Key Weirs by Studying the Effect of Crest Slope in Input and Output keys

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Numerical Simulation of Flow in Piano Key Weirs by Studying the Effect of Crest Slope in Input and Output keys

ارائه دهنده: Provider: Mahya Rahimi yeganeh

اساتید راهنما: Supervisors: Dr Jalal Sadeghiyan

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr Jalal Akbari & Dr Bahram Rezayi

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 43

چکیده: Abstract: Weirs are hydraulic structures designed to discharge excess floodwater beyond the storage capacity of a dam. One type of spillway with particular relevance in dam engineering is the Piano Key Weir (PKW). These weirs, with their unique design, have a higher discharge capacity compared to conventional or liner weirs. This study numerically investigates the effect of the ramp angle at the inlet and outlet keys of PKWs on flow patterns, flow surface profiles, discharge coefficients, and weir efficiency. In this regard, six ramp angles (15°, 30°, 45°, 60°, 75°, and 90°) were selected for five different water head-to-weir height ratios (H/P) ranging from 0.23 to 0.70, with a constant weir height (P) of 0.15 meters. The FLOW-3D software was used for flow simulations. A comparison of the numerical results with the experimental data from Ashja Arvan (1401) showed that the mean absolute error (MAE) for the flow depth at the weir crest (H) was 0.009 m, and for the discharge coefficient, it was 0.037. The mean relative percentage error (APE) for the flow depth at the crest was 4.08%, and for the discharge coefficient, it was 6.51%, indicating the high accuracy of the simulation model in predicting the flow through PKW models. The results of the flow surface profiles demonstrated that at low H/P ratios, the flow surface showed a greater drop level, and as the ramp angle decreased from 90° to 15°, this drop reduced, and the flow jets were transported downstream more quickly. Compared to other models, the PKW with a 90° ramp angle passed more flow, and the flow depth downstream was greater than in other models. The flow jet behavior showed that in all models and at low H/P ratios, the flow jet adhered to the weir wall, indicating the need for an aeration system. However, as the H/P ratio increased, the flow jet became aerated and submerged, eliminating the need for aeration. The ramp angle in the outlet key transferred the location of the flow detachment from the sides to the upstream of the weir, preventing flow interaction at the weir's outlet. The PKW with a 90° ramp angle exhibited better performance in transferring flow downstream compared to other PKW models. In the investigation of discharge coefficient and spillway efficiency variations with varying ramp angles, it was found that as the ramp angle increased, the discharge coefficient, efficiency, and flow rate passing through the weir increased. In all models, the highest discharge coefficient, efficiency, and flow rate were observed for the 90° ramp angle. Specifically, at a low H/P ratio (H/P = 0.23), increasing the ramp angle from 15° to 90° resulted in a 21.66% increase in the discharge coefficient and a 21.66% increase in efficiency. As the H/P ratio increased, the discharge coefficient and efficiency decreased. The results were consistent with previous studies. Increasing the weir height from 0.10 meters to 0.15 m resulted in a 65.36% increase in the discharge coefficient and a 68.39% increase in the discharge flow. Finally, comparing the results of the present study with other studies revealed that PKWs with triangular noses perform better than those with rectangular noses. Additionally, on average, the efficiency of the triangular labyrinth weir was 2.42% higher than that of the trapezoidal-crested labyrinth weir and 37.50% higher than the rectangular PKW with a 90° ramp angle.

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