Abstract

Turbulent phenomenon in braided rivers is much more complex compared to the straight and meandering rivers. The turbulent flow structure at locations upstream and downstream of the mid-channel are analysed experimentally and numerically by plotting the vertical profiles of velocity and turbulent parameters. Fluent Computational Fluid Dynamics (CFD) code is used to satisfactorily validating the experimental measurements. Reynolds stress model (RSM) is used in the numerical simulation as a turbulence model. The observation of the vertical profile of turbulent parameters found the submergence ratio greatly influences the flow structure in the vicinity of bar. The effect of submergence ratio (ratio of bar height to flow depth) on the flow structure is analysed by using the depth-wise profile of velocity and turbulent parameters. The studies concluded that: (1) For region upstream of bar, the low value of longitudinal velocity and negative value of vertical velocity leads to the region susceptible to scouring; (2) The bar height has a significant effect on the flow turbulence in its vicinity. The value of total turbulent intensity at points downstream of mid-channel bar is much more as compared to upstream points. This is mainly due to the vortex shedding in the downstream region of bar; (3) RSM CFD code is satisfactorily validating the depth-wise profile of turbulent and velocity distributions yielded from experimental results. 4) The sweep event is dominant in the near bed region (z/h < 0.1) for sections upstream of bar. For region near (z/h = 0.1), there is canceling effect (sweep vs ejection) which leads to the value of S_u and S_w tends to zero in that region; 5) For points downstream of bar at region (z/h < 0.1), the positive value of S_u and S_w indicate the dominance of outward interaction event.

中文翻译：

---

中通道杆速度和湍流强度的实验和数值研究

摘要

辫状河流的湍流现象比笔直和蜿蜒的河流要复杂得多。通过绘制速度和湍流参数的垂直剖面图，对中间通道上游和下游位置的湍流结构进行了实验和数值分析。Fluent 计算流体动力学 (CFD) 代码用于令人满意地验证实验测量。雷诺应力模型 (RSM) 在数值模拟中用作湍流模型。对湍流参数垂直剖面的观察发现，淹没比对巴附近的流动结构有很大影响。通过使用速度和湍流参数的深度分布来分析淹没比（杆高度与流动深度的比率）对流动结构的影响。研究得出以下结论：(1)对于坝体上游区域，纵向速度值偏低，垂向速度值为负值，导致该区域易受冲刷；(2) 钢筋高度对其附近的流动湍流有显着影响。与上游点相比，中通道坝下游点的总湍流强度值要大得多。这主要是由于棒下游区域的涡流脱落；(3) RSM CFD 代码令人满意地验证了从实验结果产生的湍流和速度分布的深度剖面。4）波及事件在近床区（(2) 钢筋高度对其附近的流动湍流有显着影响。与上游点相比，中通道坝下游点的总湍流强度值要大得多。这主要是由于棒下游区域的涡流脱落；(3) RSM CFD 代码令人满意地验证了从实验结果产生的湍流和速度分布的深度剖面。4）波及事件在近床区（(2) 钢筋高度对其附近的流动湍流有显着影响。与上游点相比，中通道坝下游点的总湍流强度值要大得多。这主要是由于棒下游区域的涡流脱落；(3) RSM CFD 代码令人满意地验证了从实验结果产生的湍流和速度分布的深度剖面。4）波及事件在近床区（(3) RSM CFD 代码令人满意地验证了从实验结果产生的湍流和速度分布的深度剖面。4）波及事件在近床区（(3) RSM CFD 代码令人满意地验证了从实验结果产生的湍流和速度分布的深度剖面。4）波及事件在近床区（z / h < 0.1) 用于钢筋上游的部分。对于靠近 ( z / h = 0.1) 的区域，存在抵消效应（扫描 vs 喷射），导致该区域中S _u和S _w的值趋于零；5) 对于区域( z / h < 0.1) bar 下游的点，S _u和S _w的正值表示外向交互事件占主导地位。