مطالعه آزمایشگاهی تأثیر ایجاد پلکان بر روی تندآب بر تغییرات آب‌شستگی موضعی در پایین‌دست پرتاب‌کننده جامی شکل

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه مهندسی آبیاری و آبادانی، دانشکدگان کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران،

2 گروه مهندسی آبیاری و آبادانی، دانشکدگان کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران.

3 گروه مهندسی آب دانشگاه گیلان، دانشکده علوم کشاورزی، دانشگاه گیلان، رشت، ایران.

چکیده

یکی از موضوعاتی که در طراحی سد‌های مخزنی اهمیت زیادی داشته و همواره مورد توجه محققین است، کاهش انرژی جنبشی جریان عبوری از سرریز آن‌ها به منظور کنترل سرعت، کاهش انرژی مخرب ناشی از آن و نیز کاستن از عمق آب‌شستگی در پایین‌دست سرریزها می‌باشد. تندآب‌های پلکانی و پرتاب‌کننده‌های جامی شکل متداول‌ترین سازه‌های مستهلک‌کننده انرژی در سرریز‌های اضطراری در سد‌ها هستند. با توجه به تأثیری که عمق آب‌شستگی در پایین‌دست این سازه‌ها بر ایمنی و پایداری آن‌ها دارد، در تحقیق حاضر تأثیر پارامترهای هیدرولیکی و هندسی بر تغییرات مشخصات آب‌شستگی در پایین‌دست تندآب‌های ساده و پلکانی همراه با پرتا‌ب‌کننده جامی‌شکل به‌صورت آزمایشگاهی مورد بررسی قرار گرفت. آزمایش‌های این تحقیق در آزمایشگاه هیدرولیک دانشگاه گیلان در سال 1399-1400 برای نسبت عمق‌ بحرانی به ارتفاع پله (yc/h) در دامنه 53/0 تا 97/0، زاویه‌های جت خروجی 15 و 30 درجه پرتاب‌کننده جامی شکل، نسبت عمق پایاب به عمق بحرانی (ht/yc) در دامنه 5/1 تا 2، نسبت ارتفاع ریزش به ارتفاع پله (HF/h) در دامنه 2 تا 4 و شیب تندآب 1:2 انجام گردید. مقایسه نتایج به‌دست آمده نشان می‌دهد که با ایجاد پلکان بر روی نیمرخ تندآب، حد اکثرعمق آب‌ شستگی در پرتاب‌کننده جامی شکل با زاویه‌های جت خروجی 15 و 30 درجه نسبت به تندآب ساده برای عمق بحرانی نسبی حداقل به ترتیب به میزان 22 و 35 درصد و در عمق بحرانی نسبی حداکثر به ترتیب به میزان 13 و 20 درصد کاهش می‌یابد. همچنین با افزایش زاویه جت خروجی پرتاب‌کننده جامی شکل از 15 به 30 درجه، حداکثر عمق آب‌شستگی به طور متوسط برای دو عمق پایاب حداقل و حداکثر در تندآب ساده به ترتیب 18 و 11 درصد و برای تندآب پلکانی به ترتیب 19 و 17 درصد کاهش می‌یابد. علاوه براین رابطه رگرسیونی برای تخمین حداکثر عمق آب‌شستگی برای تندآب پلکانی همراه با پرتاب‌کننده جامی شکل ارائه شد.

کلیدواژه‌ها

عنوان مقاله [English]

Experimental investigation of the effect of implementing steps over chute on local scour variations downstream of a flip bucket

نویسندگان [English]

  • Amir Rajaei 1
  • Mohammad Hosein Omid 2
  • Mahdi Esmaeili Varaki 3
1 PhD Candidate, Irrigation and Reclamation Engineering, Department, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
2 Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
3 Department of Water Engineering, Faculty of Agriculture Science, University of Guilan, Rasht, Iran.
چکیده [English]

One of the issues that researchers have always considered in the design of storage dams is reducing the kinetic energy of flow passing through the spillways to control the velocity, reduce the destructive energy, and scour depth downstream of spillways. Stepped chutes and flip buckets are the most common energy dissipator structures in emergency spillways at dams. Regarding the effect of scour depth at downstream of these structures on their stability and safety, in the present study, the effect of hydraulic and geometric parameters on variations of scour characteristics downstream of smooth and stepped chutes was investigated experimentally. Experiments were conducted at a hydraulic lab at the University of Guilan in 2020-2021 with a ratio of critical flow depth and step height (yc/h) of 0.53-0.97, bucket exit angles of 15° and 30°, the ratio of tailwater and critical flow depth (ht/yc) ranging from 1.5–2, the ratio of height falling and step height (HF/h) varied in the range of 2-4, and a spillway slope of 1:2 (V: H). The comparison of results demonstrated that implementing steps over a smooth chute profile reduced maximum downstream scour depth of the flip bucket by 15° and 30° exit angles in comparison with a smooth chute for the minimum relative critical flow depth by 22 and 41 percent, respectively, and for the maximum relative critical flow depth, by 14 and 20 percent, respectively. Also, with an increase in the exit angle from 15° to 30°, the maximum scour depth decreases for the minimum and maximum tailwater depths by an average of 18 and 11 percent, respectively, for a smooth chute and by an average of 19 and 17 percent, respectively, for a stepped chute. Furthermore, a regression relationship was derived for predicting the scour depth at downstream of stepped chutes with the flip bucket.

کلیدواژه‌ها [English]

  • bucket exit angle
  • Energy dissipator
  • Flip buckets
  • Scour reduction
  • Stepped spillway

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