اثر مقیاس بر پروفیل سطح آب در سرریز اوجی با انحنا در پلان و با دیواره های جانبی همگرا

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشگاه سیستان و بلوچستان

2 پژوهشکده حفاظت خاک و آبخیزداری

چکیده

اطلاع از پروفیل سطح جریان روی سرریز برای طراحی ارتفاع آزاد و ارتفاع دیوارۀ سرریز اهمیت دارد که مهندسان طراح از مدلسازی فیزیکی برای طراحی این نوع سازه ­ها استفاده می­ کنند، از این­رو اثر مقیاس در مدلسازی سرریز باعث اختلاف داده­ های اندازه ­گیری شده بین مدل و نمونه اصلی می ­شود. در این تحقیق، مدل آزمایشگاهی سرریز سد گرمی­ چای میانه در سه مقیاس 1:100، 1:75 و 1:50 ساخته و پروفیل سطح آب روی سرریز، با هفت دبی اندازه­ گیری شد؛ همچنین، درصد اختلاف ارتفاع سطح آب دو مدل فیزیکی با مقیاس 1:100 و 1:75 نسبت به مدل با مقیاس مبنا (مقیاس 1:50) محاسبه شد. نتایج بررسی­ ها و مشاهدات نشان می­ دهد که در نسبت دبی به دبی طراحی برابر 0/3، به­­ دلیل تأثیر زیاد لزوجت و کشش سطحی میزان اختلاف ارتفاع سطح آب در مدل با مقیاس 1:100 و 1:75 نسبت به مقیاس مبنا به‌ترتیب برابر 18/4 و 15/6 درصد است. دبی­ های بزرگ‌تر که ارتفاع آب روی سرریز افزایش می­ یابد، باعث کاهش تأثیر نیروی لزوجت و کشش سطحی می­ شود که در نسبت دبی به دبی طراحی 1/18 میزان اختلاف ارتفاع سطح آب در مقیاس 1:100 و 1:75 به‌ترتیب برابر 5/8 و 4/8 درصد است. در این تحقیق، میزان تأثیر لزوجت و کشش سطحی با ارائۀ رابطۀ اصلاحی (ʹK) که تابع رینولدز و وبر بوده بیان و مشخص گردید که با مدلسازی سرریز اوجی با انحنا در پلان و با دیوارۀ جانبی همگرا می­توان در اعداد رینولدز بزرگ‌تر از 104*3/1 از اثر لزوجت و در اعداد وبر بزرگ‌تر از 270 از اثر کشش سطحی صرف ­نظر کرد و نتایج نمونه اصلی را با برون ­یابی از مطالعات مدل به ­دست آورد.

کلیدواژه‌ها


عنوان مقاله [English]

Scale Effect of the Water Surface Profile on Ogee Spillway with Curvature in Plan and Converging Training Walls

نویسندگان [English]

  • Jalal SheikhKazemi 1
  • Mojtaba Saneie 2
  • Mehdi Azhdary-Moghadam 1
چکیده [English]

The water surface profiles on spillway are important for design of free board and spillway training wall height. The engineers have used physical modeling to design these kinds of structures, Considering that the scale effect in the spillway modeling, leads to the different measured data between model and prototype, in this study, an experimental model based on Garmi-Chay Mianeh dam spillway was designed in three 1:100, 1:75, and 1:50 scales. Next, the water surface profile on spillway crest measured in seven discharges and compared with
basic scale of (1:50), the percentage of water level difference on the crest calculated in two
physical models with 1:100 and 1:75 scales.  Results and observations revealed that in
   due to the effect of viscosity and surface tension the difference of water level in the scale of 1:100 and 1:75 was 18.4% and 15.6% respectively, relative to the base scale. The larger discharge, water level on spillway increases, leads to decrease viscosity and surface tension effects. For  the difference in water level in the scale of 1:100 and 1:75 was 5.8% and 4.8% respectively relative to the base scale. In this study, viscosity and surface tension effects is stated with correction equation (K'), that was functions of Reynolds and Weber numbers. With the ogee spillway modeling the effect of viscosity in Reynolds numbers larger than 3.1*104 and the effect of tension surface in Weber numbers larger than 270 can be neglected and by extrapolation prototype results from model studies can be obtained.

کلیدواژه‌ها [English]

  • ogee spillway
  • Scale Effect
  • Surface Tension
  • viscosity
  • Water Surface Profile

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