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<p>To clarify the complex hydrodynamics of bend-straightened reaches of continuous bend channels, three-dimensional simulations were performed with a Reynolds Stress Model (RSM) coupled to the Volume of Fluid (VOF) method. The numerical experiments examined water-surface fluctuations, velocity structures, and turbulent kinetic energy under varying planform geometries, characterized by the junction angle <i>α</i> and curvature <i>K</i>, and under different Froude numbers <i>Fr</i>. Related implications for channel stability, ecological functions, and navigation management were also assessed. The results indicate that all hydraulic parameters exhibit an approximately linear dependence on <i>Fr</i>, while being jointly modulated by <i>α</i> and <i>K</i>. Streamwise velocity deflection and secondary flow structures generated in the upstream unit persist into the downstream unit, leading to average increases of 3.7% in the discharge fraction diverted into straight channels, 17.1% in secondary flow intensity within the confluence, and approximately 7% in separation zone size. The inherited secondary flow explains about 70% of the discharge difference, whereas streamwise-momentum eccentricity accounts for the remaining about 30%. For <i>Fr</i> &gt; 0.3, backwater induced at the downstream bifurcation propagates upstream and raises the water level in the upstream confluence, thereby reducing the net water surface slope; the upstream slope is at least 15% smaller than that downstream. From an engineering perspective, straight channels favor navigation but may promote differential bed adjustment and re-curving tendencies, whereas bend channels provide low velocity refugia for aquatic habitats and exhibit a long-term tendency to migrate downstream.</p>

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Flow structure characteristics in bend-straightened reaches of continuous bend channels

  • 期刊论文

  • 发表日期：

    2026年4月30日

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  • Liang Zhong,
  • Xinming Yan,
  • Jian Pan,
  • Xin Guan,
  • Xiangyu Xu

摘要

To clarify the complex hydrodynamics of bend-straightened reaches of continuous bend channels, three-dimensional simulations were performed with a Reynolds Stress Model (RSM) coupled to the Volume of Fluid (VOF) method. The numerical experiments examined water-surface fluctuations, velocity structures, and turbulent kinetic energy under varying planform geometries, characterized by the junction angle α and curvature K, and under different Froude numbers Fr. Related implications for channel stability, ecological functions, and navigation management were also assessed. The results indicate that all hydraulic parameters exhibit an approximately linear dependence on Fr, while being jointly modulated by α and K. Streamwise velocity deflection and secondary flow structures generated in the upstream unit persist into the downstream unit, leading to average increases of 3.7% in the discharge fraction diverted into straight channels, 17.1% in secondary flow intensity within the confluence, and approximately 7% in separation zone size. The inherited secondary flow explains about 70% of the discharge difference, whereas streamwise-momentum eccentricity accounts for the remaining about 30%. For Fr > 0.3, backwater induced at the downstream bifurcation propagates upstream and raises the water level in the upstream confluence, thereby reducing the net water surface slope; the upstream slope is at least 15% smaller than that downstream. From an engineering perspective, straight channels favor navigation but may promote differential bed adjustment and re-curving tendencies, whereas bend channels provide low velocity refugia for aquatic habitats and exhibit a long-term tendency to migrate downstream.