Influence of deflection angles on flow behaviours in open-channel bends Influence of deflection angles on flow behaviours in open-channel bends

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Vol15 No.10: 2292-2306

Title】Influence of deflection angles on flow behaviours in open-channel bends

Author】LI Bing-dong1; ZHANG Xin-hua1*; TANG Han-song2; TSUBAKIRyota3

Addresses】1 State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China; 2 Department of Civil Engineering/City College, City University of New York, New York 10031, USA; 3 Department of Civil Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan

Corresponding author】ZHANG Xin-hua

Citation】Li BD, Zhang XH, Tang HS, et al. (2018) Influence of deflection angles on flow behaviours in open-channel bends. Journal of Mountain Science 15(10). https://doi.org/10.1007/s11629-018-4848-y

DOI】https://doi.org/10.1007/s11629-018-4848-y

Abstract】The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation oneffects of deflection angles (30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group (RNG) κ-ε model and a volume of fluid (VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is a low-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.

Keywords】Open channel; Deflection angle; Transverse slopeof water surface; Secondary flow; Shear stress