بررسی آزمایشگاهی توان جریان ثانویه در پیچ رودخانه

نویسندگان

چکیده

شناخت جریان عرضی قوی ناشی از نیروی گریز از مرکز در پیچان‌رودها سبب شناخت مکان‌ بیشینه فرسایش در ساحل خارجی می‌شود. از ‌این‌رو با شناخت مکان‌های مناسب برای احداث دهانه آبگیر و انجام عملیات مناسب مهندسی رودخانه می‌توان از تخریب سازه‌ها و زمین‌های زراعی اطراف رودخانه جلوگیری کرد. در این مقاله به بررسی آزمایشگاهی توان جریان ثانویه و تغییرات آن در پیچ رودخانه و مدل‌های پیش‌بینی مکان بیشینه فرسایش عرضی پرداخته شده است. آزمایش‌های این پژوهش در یک پیچ تند با نسبت شعاع مرکزی به عرض 31‎/1 در یک توپوگرافی توسعه یافته و سه دبی 63،‏ 89 و 104 لیتر بر ثانیه انجام شده است. بررسی‌ها نشان‌گر هماهنگی کامل جریان ثانویه با تغییرات شیب عرضی بستر و کاهش توان جریان ثانویه با افزایش دبی می‌باشد. به بیان واضح‌تر نسبت انرژی جنبشی عرضی به طولی از 43 درصد در دبی 63 لیتر بر ثانیه به 35 درصد در دبی 104 لیتر بر ثانیه کم شده است. همچنین مکان دهانه آبگیر در پیچ تند در حدود یک سوم از ورودی پیچ به دست آمده است. علاوه ‌بر آن،‏ بررسی مدل‌های تأخیر فاز جریان ثانویه نشان داد که آن‌ها توانایی پیش‌بینی صحیح مکان بیشینه فرسایش را ندارند. دلیل این امر عدم درنظرگرفتن تندی پیچ (نسبت شعاع مرکزی به عرض کانال) است که روی الگوی جریان عرضی تأثیر بسزایی دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Experimental investigation of secondary flow strength in the river bends

نویسندگان [English]

  • Dr A. Samadi
  • Javad Mozaffari
  • Seyed Asadollah Mohseni Movahed
چکیده [English]

Understanding of the strong transversal flow due to centrifugal force in meanders leads to detecting the location of maximum erosion in outer bank. By identifying the best sites for constructing the intake structures and proper river training techniques, it is possible to prevent destruction of structures and farmlands which located near the rivers. This article focuses on the experimental study of secondary flow strength, its changes in meanders and models predicting the location of the maximum lateral erosion rate. The experiments are carried out at a sharp bend with the central radius-width ratio of 1.31 on a developed topography and discharges of 63, 89 and 104 liter per second. Investigations indicate a complete correlation between secondary flow and transversal bed slope and also between the reduction of the secondary flow strength and increasing discharge. To make it clear, the ratio of transverse to longitudinal kinetic energy has dropped from 43 percent at discharge rate 63 liter per second to 35 percent at discharge rate 104 liter per second. Also, the place of the intake on sharp bend can be in 1/3 from the entrance of the bend. Moreover, evaluation of phase lag models in the secondary flow showed that they lack the ability to correctly predict the location of maximum erosion. It may be the result of disregard for the sharpness of the bend (the ratio of central radius to canal width) which is highly effective for transversal flow pattern.
Keywords: Secondary flow, river bend, lateral erosion, sharp bend

Understanding of the strong transversal flow due to centrifugal force in meanders leads to detecting the location of maximum erosion in outer bank. By identifying the best sites for constructing the intake structures and proper river training techniques, it is possible to prevent destruction of structures and farmlands which located near the rivers. This article focuses on the experimental study of secondary flow strength, its changes in meanders and models predicting the location of the maximum lateral erosion rate. The experiments are carried out at a sharp bend with the central radius-width ratio of 1.31 on a developed topography and discharges of 63, 89 and 104 liter per second. Investigations indicate a complete correlation between secondary flow and transversal bed slope and also between the reduction of the secondary flow strength and increasing discharge. To make it clear, the ratio of transverse to longitudinal kinetic energy has dropped from 43 percent at discharge rate 63 liter per second to 35 percent at discharge rate 104 liter per second. Also, the place of the intake on sharp bend can be in 1/3 from the entrance of the bend. Moreover, evaluation of phase lag models in the secondary flow showed that they lack the ability to correctly predict the location of maximum erosion. It may be the result of disregard for the sharpness of the bend (the ratio of central radius to canal width) which is highly effective for transversal flow pattern.
Keywords: Secondary flow, river bend, lateral erosion, sharp bend

Understanding of the strong transversal flow due to centrifugal force in meanders leads to detecting the location of maximum erosion in outer bank. By identifying the best sites for constructing the intake structures and proper river training techniques, it is possible to prevent destruction of structures and farmlands which located near the rivers. This article focuses on the experimental study of secondary flow strength, its changes in meanders and models predicting the location of the maximum lateral erosion rate. The experiments are carried out at a sharp bend with the central radius-width ratio of 1.31 on a developed topography and discharges of 63, 89 and 104 liter per second. Investigations indicate a complete correlation between secondary flow and transversal bed slope and also between the reduction of the secondary flow strength and increasing discharge. To make it clear, the ratio of transverse to longitudinal kinetic energy has dropped from 43 percent at discharge rate 63 liter per second to 35 percent at discharge rate 104 liter per second. Also, the place of the intake on sharp bend can be in 1/3 from the entrance of the bend. Moreover, evaluation of phase lag models in the secondary flow showed that they lack the ability to correctly predict the location of maximum erosion. It may be the result of disregard for the sharpness of the bend (the ratio of central radius to canal width) which is highly effective for transversal flow pattern.

کلیدواژه‌ها [English]

  • Secondary flow-sharp bend-river bend-lateral erosion-