بررسی آزمایشگاهی نوسانات فشار پرش هیدرولیکی در حوضچه آرامش با واگرایی ناگهانی و بستر زبر

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه عمران، واحد چالوس، دانشگاه آزاد اسلامی، چالوس، ایران

2 استادیار، گروه عمران، واحد چالوس، دانشگاه آزاد اسلامی، چالوس، ایران

چکیده

حوضچه­های آرامش با واگرایی ناگهانی از جمله سازه­های مستهلک­کننده انرژی ناشی از پرش هیدرولیکی هستند. اثر فشارهای نوسانی ناشی از تلاطم در پرش هیدرولیکی موجب آسیب قابل‌توجهی در حوضچه می­شود و لازم است در طراحی سازه­ها مورد توجه قرار گیرد. از طرفی وجود زبری در بستر باعث تغییر دادن رفتار خطوط جریان و تشکیل گردابه­ها در طول پرش می‌شود. از این ‌رو مطالعه نوسانات فشار تحت شرایط مختلف آزمایشگاهی امری ضروری است. در پژوهش حاضر به بررسی اثر حضور زبری بر فشارهای هیدرودینامیکی در پرش هیدرولیکی نوع S در مقاطع واگرای ناگهانی پرداخته شد. برای این منظور آزمایش­ها در یک کانال نسبتاً بزرگ به عرض 8/0 و طول m 12 در حوضچه آرامش با نسبت­های واگرایی 33/0، 5/0، 67/0 و 1 در محدوده اعداد فرود بین 2 تا 5/9 انجام شد. همچنین المان­های زبری با ارتفاع 3 سانتی متر و فواصل مشخص در بستر کانال و در پایین­دست مقطع واگرایی جای­گذاری شد. به ‌منظور بررسی اثرات زبری در میزان فشارهای هیدرودینامیکی، آزمایش­ها در دو مرحله مجزا شامل بستر حوضچه کاملاً صاف و بدون حضور زبری در مرحله اول (77 آزمایش) و با حضور زبری در کف حوضچه در مرحله دوم (81 آزمایش) صورت پذیرفت. نتایج نشان می­دهد که وجود زبری در بستر باعث کاهش شدت نوسانات فشار در حوضچه آرامش می‌شود. همچنین در مقاطع واگرای ناگهانی به­دلیل تشکیل گردابه­های جانبی افت انرژی افزایش و شدت نوسانات فشار کاهش می­یابد. آهنگ کاهش ماکزیمم نوسانات فشار به­ترتیب 27، 46 و 58% برای نسبت واگرایی 67/0، 5/0 و 33/0 در بستر زبر تخمین زده شد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental Determination of Pressure Fluctuations on Stilling Basin with Sudden Expanding and Roughened Bed

نویسندگان [English]

  • Marzieh Naemhasani 1
  • Kouros Nekoufar 2
  • Morteza Biglarian 2
  • Morteza Jamshidi 2
1 PhD Scholar, Department of Civil Engineering, Chalous Branch, Islamic Azad University, Chalous, Iran
2 Assist. Professor, Department of Civil Engineering, Chalous Branch, Islamic Azad University, Chalous, Iran
چکیده [English]

Introduction: Stilling basins with sudden expansions are one of the energy-dissipater structures. The application of cross-sectional expansion in channels would be a useful way to ensure the stabilization of the hydraulic jump in the stilling basins. In some previous studies, the effects of expansion on jump characteristics were investigated and study of the relationship between expansion ratio and pressure fluctuation parameters lacks in the literature. Thus, this study attempted to carry out the experimental research for evaluating the effects of different expansion ratios on pressure fluctuation, during the hydraulic jump on a roughened bed.
Materials and Methods: The experiments were conducted in a rectangular channel with 12 m length, 0.8 m width and 0.7 m depth having glass side walls. The narrow part of the flume was constructed using two Plexiglas boxes which extended 0.8 m downstream to enlarge abruptly and asymmetrically the width of the main flume. In this study four expansion ratio ( ) of 1, 0.67, 0.5, and 0.33 with 0.8, 0.53, 0.4, and 0.27 m width were considered respectively (where  is the width of the approaching flume to the expansion in upstream and  is the flume width in downstream). In order to roughening the bed, the discrete elements of roughness were made by polyethylene with the heights of 3 cm. These elements were located below the water jet and were not exposed to the incoming water jet, directly. Due to the fact that the pressure in the stilling basin’s bed has random fluctuations, analysis was mainly evaluated by statistical methods and with the help of 𝜋-Buckingham analysis. The most important pressure fluctuation parameter is the non-dimensional coefficient of . Non-dimensional pressure fluctuation parameter (Cp´) and also its maximum value (Cp´max) were calculated for all expanding ratios.
Results: The intensity of pressure fluctuations rose at the beginning of the jump, and reached its maximum value. Then, it decreased and became almost constant until the end of the jump. Cp´ parameter also decreased by increasing Froude number, because of faster growth of kinetic energy than pressure fluctuation rate. Besides, presence of bed roughness caused to decrease the pressure fluctuations intensity. The value of pressure fluctuations coefficient decreased by decreasing the expansion ratio ( ), so that this parameter in expansion ratio of 0.33 had the minimum value. On the other hand, the value of Cp´max decreased with increasing the Froude number in both smooth and rough bed. Due to presence of bed roughness, Cp´max decreased by an average of 20% than in smooth bed. Considering the simultaneous impact of bed roughness and expansion ratio, it can be concluded that Cp´max decreases by an average of 27% in expansion ratio of 0.67. Moreover, in expansion ratio of 0.5 and 0.33, the reduction rate of Cp´max achieved almost 46 and 58%, respectively. As a result, presence of both factors of roughness and expansion, lead to reduce the non-dimensional parameter of Cp´max.
Conclusion: In summary, the results showed that both bed roughness and sudden expanding basin lead to decreasing the pressure fluctuation intensity due to producing lateral vorticities and eddies and increasing the energy loss in the basin. Therefore, the reduction rate of maximum pressure fluctuation in rough bed was 20, 27, 46, and 58% for expansion ratio of 1, 0.67, 0.5, and 0.33, respectively rather than smooth bed.

کلیدواژه‌ها [English]

  • Abrupt Expanding
  • Hydraulic jump
  • Pressure Fluctuations
  • Rough Stilling Basin
Alhamid, A. A. (2004). S-jump characteristics on sloping basins. J. Hydraul. Res., 42(6), 657-662.
Bejestan, M. S. and Neisi, K. (2009). A new roughened bed hydraulic jump stilling basin. Asian J. Appl. Sci., 2(5), 436- 445.
Buckingham, E. (1914). On physically similar systems; illustrations of the use of dimensional equations. Phys. Rev., 4(4), 345.
Chanson, H. (2011). Hydraulic jumps: turbulence and air bubble entrainment. J. Houille Blanche, 3, 5–16.
Daneshfaraz, R., Sadeghi, H., Rezazadeh Joudi, A. and Abraham, L. (2017). Experimental investigation of hydraulic jump characteristics in contraction and expansions. J. Eng. Nat. Sci./Mühendislik ve Fen Bilimleri Dergisi, 35(1), 87-91
Daneshfaraz, R., Majediasl, M., Mirzaee, R., Parsamehr, P. (2019). Experimental study of the roughness bed with non-continuous trapezoidal elements on S-jump characteristics in the non-prismatic rectangular channel. Sharif J. Civil Eng., [In Persian].
Ead, S. Rajaratnam, N. (2002). Hydraulic jumps on corrugated beds. J. Hydraul. Eng., 128(7), 656–663.
Hassanpour, N., Hosseinzadeh Dalir, A., Farsadizadeh, D., and Gualtieri, C. (2017). An experimental study of hydraulic jump in a gradually expanding rectangular stilling basin with roughened bed. Water, 9(12), 945.
Hosseini, D., Torabi, M. and Moghadam, M. A. (2019). Preference assessment of energy and momentum equations over 2D-SKM method in compound channels. J. Water Resour. Eng. Manag., 6(1) 24-34.
Imran, H. M. and Akib, S. (2013). A review of hydraulic jump properties in different channel bed conditions. Life Sci. J., 10(2), 126-130.
Izadjoo, F. and Shafai Bejestan, M. (2007). Corrugated bed hydraulic jump stilling basin. J. Appl. Sci, 7, 1164–1169.
Karimi, M., Mousavi Jahromi, H. and Shafai Bajestan, M. (2014). The effect of roughness in pressure fluctuations in the stilling basin with sudden expansion. J. Water Soil Conserv., 4(1), 63-78 [In Persian].
Kato, F., Sato, S. and Yeh, H. (2000). Large-scale experiment on dynamic response of sand bed around a cylinder due to tsunami. Int. J. Coast. Eng., 1848-1859.
Kuswandi, R. and Triatmadja, R., (2019). The use of dam break model to simulate tsunami runup and scouring around a vertical cylinder. J. Appl. Fluid Mech., 12(5), 1395-1406.
Liu, Y., Zhang, D., Wu, J., Zhang, D. and Yang, M. (2020). Roughened bed stilling basin and its hydraulic jump characteristics, IOP Conf. Ser.: Mater. Sci. Eng., 758 (1), 12082.
Lopardo, R. A. and Romagnoli, M. (2009). Pressure and velocity fluctuations in stilling basins. Adv. Water Resour. Hydraul. Eng., 2093–2098. doi:10.1007/978-3-540-89465-0_359. 
Matin, M. A., Hasan, M. R. and Islam, M. A. (2008). Experiment on hydraulic jump in sudden expansion in a sloping rectangular channel. J. Civil Eng., 36(2), 65-77.
Neisi, K. and Shafai Bajestan, M. (2013). Characteristics of S-jump on roughened bed stilling basin. J. Water Sci. Res., 5(2), 25-34.
Parsamehr, P., Farsadizadeh, D., HosseinzadehDalir, A., Abbaspour, A. and Nasr Esfahani, M. J. (2017). Characteristics of hydraulic jump on rough bed with adverse slope. ISH J. Hydraul. Eng., 23(3), 301-307.
Rajaratnam, N. (1968). Hydraulic jump on rough bed. Trans. Eng. Instit. Can., 11(A-2).
Sadeghfam, S., Akhtari, A., Daneshfaraz, R. and Tayfur, G. (2015). Experimental investigation of screens as energy dissipaters in submerged hydraulic jump. Turk. J. Eng. Environ. Sci., 38(2), 126-138.
Samadi-Boroujeni, H., Ghazali, M., Gorbani, B., Fattahi Nafchi, R. (2013). Effect of triangular corrugated beds on the hydraulic jump characteristics. Can. J. Civ. Eng. 40(9), 841–847.
Torabi, M., Shafieefar, M. (2015). An experimental investigation on the stability of foundation of composite vertical breakwaters. J. Marine Sci. Appl., 14(2), 175-182.
Torabi, M., Hamedi, A., Alamatian, A., Zahabi, H. (2019). The effect of geometry parameters and flow characteristics on erosion and sedimentation in channels junction using finite volume method. Int. J. Eng. Manag. Res., 9. DOI: 10.31033/ijemr.9.2.14.
Torkamanzad, N., Hosseinzadeh Dalir, A., Salmasi, F., and Abbaspour, A. (2019). Hydraulic jump below abrupt asymmetric expanding stilling basin on rough bed. Water, 11(9), 1756.
Wu, J. H., Licheng, C. Z., Ma F., Li, T. C. and Wu, W. W. (2015). Hydraulics of crest spillway with large unit discharge and low Froude number. J. Hydrodynam., Ser. B, 27(2), 242-247.
Yan, Z., Zhou, C. and Lu, S. (2006). Pressure fluctuations beneath spatial hydraulic jumps. J. Hydrodynam., Ser. B, 18(6), 723–726.
Zahabi, H., Torabi, M. Alamatian, E., Bahiraei, M. and Goodarzi, M. (2018). Effects of Geometry and hydraulic characteristics of shallow reservoirs on sediment entrapment. Water, 10(12), 17-25. 
Zare, H. K. and Doering, J. C. (2010) Forced hydraulic jumps below abrupt expansions. J. Hydraul. Eng., 137(8), 825-835.