闸坝下游冲刷坑形态三维数值模拟

发布时间：2018-11-06 20:08

【摘要】：低水头枢纽具有水头低、流量大、低佛汝德数、消能不充分、闸坝建在覆盖层较厚的砂砾石河床上等特点,因此闸坝下游护坦、海漫发生冲刷破坏的现象较为普遍,甚至导致建筑物损毁,直接影响着泄水闸的安全运行。因此,正确地预测闸坝下游冲刷坑流场信息、冲刷坑形态及最大冲刷深度,对于泄水建筑物的安全运行有着非常重要的意义。本文基于Fluent动网格技术,对巨亭水电站泄水闸下游局部冲刷进行了三维数值模拟,得到了以下主要结论:(1)采用RNG k-ε湍流模型,结合SIMPLEC算法,利用VOF多相流模型追踪泄水闸下游复杂的自由水面,模拟得到了巨亭水电站泄水闸下游冲刷坑三维流场分布,通过分析对比泄流量、沿程水面线和垂线流速分布等结果表明,数值模拟值与模型试验实测值吻合良好,说明数学模型计算准确,结果可信。(2)基于Fluent动网格技术,采用VOF模型追踪自由水面,在对Fluent软件进行二次开发中,以床面水流剪切应力大于泥沙起动切应力作为网格移动的判别标准,基于弹簧光顺模型及局部网格重构模型,对单个桥墩局部冲刷进行了三维数值模拟,得到的冲刷坑形态及最大冲刷深度与模型试验结果吻合良好,验证了本文二次开发子程序的可靠性。(3)实现了泄水闸下游局部冲刷坑冲刷过程的三维数值模拟,得到的冲刷坑形态及最大深度与物理模型实测值吻合良好。(4)在冲刷坑的冲刷过程中,床面切应力逐渐减小;中轴面湍动能的变化规律与湍动能耗散率的变化规律基本相似。在冲刷初始阶段,挑坎末端床面附近的湍动能和湍动能耗散率均较大;随着冲刷的进行,冲刷后的湍动能和湍动能耗散率明显减小;在冲刷坑达到平衡状态时,冲刷坑区域的湍动能和湍动能耗散率均较小。
[Abstract]:The low head hub has the characteristics of low head, large discharge, low Froude number, insufficient energy dissipation, and the dam is built on the sand and gravel river bed with thick overburden. Therefore, the downstream of the dam protects the dam and the sea overflows with scour damage is more common. Even lead to damage to buildings, directly affect the safe operation of the sluice. Therefore, it is very important to correctly predict the flow field information, the shape of the scour pit and the maximum scour depth of the downstream sluice dam for the safe operation of the drainage structure. Based on the Fluent dynamic grid technology, the local scour downstream of the sluice of Juting Hydropower Station is simulated by 3D numerical simulation. The main conclusions are as follows: (1) the RNG k- 蔚 turbulence model is adopted, and the SIMPLEC algorithm is used to simulate the local scour of the sluice downstream of Juting Hydropower Station. VOF multiphase flow model is used to track the complex free water surface downstream of the sluice gate, and the three-dimensional flow field distribution of the scour pit downstream of the sluice of Juting Hydropower Station is simulated. The results of analysis and comparison of the discharge, the velocity distribution along the water surface line and the vertical line, etc. The numerical simulation results are in good agreement with the measured values of the model test, which shows that the mathematical model is accurate and the results are reliable. (2) based on the Fluent dynamic grid technology, the VOF model is used to track the free water surface, and in the secondary development of Fluent software, Based on spring fairing model and local mesh reconstruction model, the local scour of a single pier is simulated with the criterion that the shear stress of the bed surface is greater than the initial shear stress of sediment. The obtained scour pit shape and maximum scour depth agree well with the model test results, which verify the reliability of the secondary development subroutine in this paper. (3) the 3D numerical simulation of the local scour pit scour process downstream of the sluice is realized. The shape and maximum depth of the scour pit are in good agreement with the measured values of the physical model. (4) during the scouring process of the scour pit, the bed shear stress decreases gradually; The law of variation of turbulent kinetic energy in central axis is similar to that of turbulent kinetic energy dissipation rate. In the initial stage of scour, the turbulent kinetic energy and turbulent kinetic energy dissipation rate near the bed surface at the end of the scour are both large, and with the scouring, the turbulent kinetic energy and turbulent kinetic energy dissipation rate after scouring obviously decrease. When the scour pit reaches equilibrium, the turbulent kinetic energy and turbulent kinetic energy dissipation rate are smaller.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV149

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