نوع مقاله : مقاله پژوهشی

نویسندگان

• رضا باوندپوری گیلان ¹
• رسول قبادیان ²
• علی آرمان ¹

¹ گروه مهندسی آب، دانشکده کشاورزی، پردیس کشاورزی و منابع طبیعی، دانشگاه رازی، کرمانشاه، ایران.

² گروه مهندسی آب، پردیس کشاورزی و منابع طبیعی، دانشگاه رازی، کرمانشاه، ایران.

چکیده

کالورت‌ها سازه‌های هیدرولیکی هستند که در تقاطع مجرای آب با جاده و موانع به کار می‌روند. انسداد کالورت از عوامل مهم کاهش کارایی و تخریب آن است. تاثیر انسداد با پیشروی در مجرای اصلی کالورت تشدید می‌یابد. پیشروی انسداد موجب ایجاد تغییرات اساسی در هیدرولیک جریان و به دنبال آن تغییر در آبشستگی پایین‌دست نسبت به حالت بدون انسداد می‌شود. در این تحقیق، تاثیر پیشروی انسداد بر آبشستگی در پایین‌دست کالورت جعبه‌ای به صورت آزمایشگاهی بررسی شد، موضوعی که در تحقیقات پیشین بررسی نشده است. به منظور شناسایی دقیق‌تر الگوی جریان، به‌ویژه در طول مجرای کالورت و اندرکنش جریان و رسوب در پایین‌دست، شبیه‌سازی عددی با نرم‌افزار FLOW-3D به­انجام رسید. آزمایش‌ها در سه شدت دبی 0/45، 0/83 و 1/24؛ چهار عمق پایاب نسبی 0/47، 1/37، 2/17 و 3/07 و سه پیشروی انسداد صفر، 0/32L و 0/5L به اجرا درآمدند که در آن L طول مجرای کالورت است. نتایج موید وابستگی عمق آبشستگی به پیشروی انسداد، شدت دبی و عمق پایاب می‌باشد. در غیاب انسداد، وجود یک عمق پایاب نسبی بحرانی، ابتدا باعث کاهش و سپس افزایش عمق آبشستگی در پایین‌دست می‌شود. بررسی نتایج در حالت انسداد 32 درصد سطح مقطع ورودی در دو پیشروی 32 و 50 درصد انسداد در مجرای کالورت نشان داد که با افزایش عمق پایاب تاثیر پیشروی انسداد بر عمق آبشستگی ناچیز می‌شود، به طوری که در عمق پایاب نسبی 3/07، مقدار حداکثر عمق آبشستگی پایین‌دست در سه حالت بدون انسداد و انسداد با پیشروی‌های 32 و 50 درصد، تفاوت چندانی ندارند. یافته‌های تحقیق حاضر می‌تواند راهکارهای مناسبی برای کنترل آبشستگی در پایین‌دست کالورت در برابر انسداد و پیشروی آن به طراحان ارائه دهد.

کلیدواژه‌ها

• آبشستگی
• انسداد ورودی
• بررسی آزمایشگاهی
• کالورت
• مدل عددی

موضوعات

• مهندسی رودخانه

عنوان مقاله [English]

Experimental and numerical investigation of the effect of blockage progression on scour downstream of box culvert

نویسندگان [English]

• Reza Bavandpoori Gilan ¹
• Rasool Ghobadian ²
• Ali Arman ¹

¹ Department of Water Engineering. Faculty of Agriculture. Campus of Agriculture and Natural Resources, Razi University. Kermanshah, iran.

² Water Engineering Department. Campus of Agriculture and Natural Resources. Razi University. Kermanshah.Iran

چکیده [English]

Introduction
Blockage in the culvert is a major factor in reducing its efficiency. The effect of culvert blockage intensifies by progress in the barrel. This study investigated the effect of blockage progression on scour downstream of box culvert using experimental tests, which hasn’t been investigated in previous research. In order to more accurately identify the flow pattern, especially along the culvert channel and the interaction of flow and sediment downstream, numerical simulations were performed with FLOW-3D software. The findings can aid engineers in considering the effects of scour and blockage in the design of more efficient culverts.
 Methodology
Using the modeling of natural phenomena in a laboratory environment, we can understand the behavior of a phenomenon in a real environment. The planned experiments were conducted in the Hydraulic Laboratory of the Water Sciences and Engineering Department at Razi University. The width, depth, and length of the flume are 0.50 m, 0.60 m, and 5.40 m, respectively. The culvert, with a length of 30 cm and a rectangular cross-section measuring 10 cm in width and 7.50 cm in height, is made of glass with a thickness of 8 mm. To ensure developed flow upon entering the culvert, it is positioned 3.60 m from the beginning of the flume. At the inlet and outlet of the culvert, a type 2 USBR transition with equal angles of convergence and divergence of 26.50 degrees is used. To control the downstream water level at the desired level, a sharp-crested weir with variable height is installed downstream of the culvert. the floor of the flume upstream of the structure is uniformly covered with concrete, and the downstream section is filled by uniform sediment with diameter of 0.85 mm and thickness of 20 cm. A total of 36 experiment were conducted with three flow rate of 2.95, 5.38 and 8.03 L/s, four downstream depth of 4.5, 10.3, 16.3 and 23 cm with three blockage scenarios 0, 0.2L and 0.32L where L is the barrel length. After reaching equilibrium in each experiment, the height of the installed weir was increased to prevent a rapid drop in water level, then the pump was turned off. After complete drainage, bed changes were recorded using a 3D scanner equipped with a Kinect camera, which had an accuracy of ±0.2 mm. The data extracted from the camera was then prepared for plotting the necessary graphs. Finally, the bed surface was carefully leveled for the next experiment.
 Results and Discussion
Based on the comparison of experimental and numerical results, it was determined that the numerical model has sufficient ability to simulate the water surface and its results are reliable. Regarding sedimentary results, comparison of the results test Q₂ y_t3 α₃₂ β₃₂ by both experimental and numerical methods showed the formation of a scour hole immediately after the end of the outlet transition and the creation of a sedimentation mound after the hole. Investigation of the effect of relative tailwater depth on scour depth in unblocked conditions showed that at a fixed relative tailwater depth, the dimensionless maximum scour depth increases with the increasing flow intensity parameter. Specifically, as the flow intensity increases from 0.45 to 1.24 at a constant tailwater depth, the flow velocity inside the culvert barrel increases, and consequently, water exits the culvert downstream with greater velocity. This increase in velocity at a fixed tailwater depth leads to higher shear stress on the bed and enhanced flow power in sediment transport and bed erosion. Regarding the effect of the progression of blockage in the culvert barrel on scour at the outlet, it can be said that when the inlet section of the culvert is blocked, the maximum scour depth downstream of the culvert decreases. The reason for this is that, in the case of fixed blockage, an eddy flow with a horizontal axis is created just behind the obstruction, causing the streamlines separate and resulting in intense turbulence in the channel, in such a way that the flow hits the culvert roof several times and then dives back toward the channel floor. This process leads to significant energy loss in the flow, reducing the flow's potential for downstream scour compared to the unblocked condition.
 Conclusions
progression of the blockage in the culvert barrel can affect the flow hydraulic within it and has notable impacts on the scour of the downstream bed. Due to the impossibility of measuring some parameters, such as the Maximum scour hole depth at desired times in the laboratory environment due to high flow turbulence, the powerful FLOW-3D numerical model was used after its calibration. The results indicated that in both conditions, with and without blockage, the maximum scour depth significantly affected by the changes in flow intensity and tailwater depth. An increase in flow intensity leads to an increase in scour depth. In unblocked conditions, there is a critical relative tailwater depth for each specified flow intensity, below which scour depth decreases with increasing tailwater depth, and above which it increases. The laboratory results showed that for a fixed tailwater depth, with an increase in flow intensity, the location of maximum scour depth moved closer to the end of the culvert outlet. The blockage at the inlet section on culvert conduit, with blockage percentages of 20% and 32%, significantly affected the erosion and turbulence of the flow downstream. Compared to the unblocked condition, the presence of the blockage created turbulence in the flow, resulting in a significant drop in flow energy, which decreased the scour depth. However, as the tailwater depth increases, the impact of blockage on scour diminishes due to reduced turbulence in the channel. Given the great importance of water structures, especially culverts, in conveying flood, it is necessary for the designer to pay special attention to the issue of downstream scour when designing the culvert, because the poor performance of the culvert in conveying water during a flood can directly target the health of human communities living downstream and the efficiency of communication infrastructure.
 Acknowledgment
We would like to thank the respected professors of the Department of Water Science and Engineering, Razi University, who prepared the necessary laboratory equipment for this research.

کلیدواژه‌ها [English]

• Scour
• Inlet blockage
• Laboratory investigation
• Culvert
• Numerical Model