【作者】 许文海；

【导师】 陈刚； 李国栋；

【作者基本信息】 西安理工大学 ， 水利工程， 2007， 博士

【摘要】 明流溢洪道(洞)是水利水电工程常用的溢流设施，由于布置的需要，引水渠往往存在一定程度的平面转向，这就导致水面产生不同程度的横向比降，甚至出现漩涡，如果其影响达到下游泄槽急流段，还有可能产生急流冲击波，致使水流自由水面波动，直接威胁泄水建筑物乃至大坝的安全。对于弧门闸门广泛采用的偏心铰和伸缩式水封方案，都要求门座侧向突扩，底部突跌，从而将闸门止水与掺气设施有机地结合起来。水流离开门座射出有压洞口后四周悬空，并沿水平与垂直两个方向扩散，与侧边墙间形成侧空腔，与跌坎下底板间形成底空腔，底侧空腔相互贯通成为有效的掺气通道，对下游固壁形成保护，但是水流冲击侧墙产生的水翅，以及冲击反射产生的低压区，也会恶化流态，甚至引发空化空蚀问题。本文在回顾总结前人研究的基础上，结合九甸峡水利枢纽工程，对双洞式明流岸边溢洪道和弧形闸门突扩突跌水流衔接控制转换段的复杂流动进行了数值模拟和试验研究，主要研究内容和成果有：(1)采用k-ε两方程紊流数学模型和VOF自由表面模拟技术，对双洞式溢洪道联合泄洪情况下库区、引水渠、溢流段和陡槽内的三维自由面流动进行了数值模拟研究。模拟得到了流速、压力分布等水力学参数，揭示了进口区域自由水面的扭曲形态。把改善进口不良流态，消除堰顶较大负压，平衡两洞间流量分配作为目标，针对溢洪洞入口地形陡峭且入口水流存在平面急剧转向的情况，提出了“椭圆曲线翼墙+悬臂直墙”的进口整流方案。通过数值模拟和模型试验的联合应用获得了理想的进水口体型与溢流堰曲线形式。(2)通过常压模型试验，对弧形闸门突扩突跌段的水力特性进行了研究。结果表明，原设计方案压力洞出口顶板和明渠段存在负压，侧墙水翅高，明渠中水流不稳，流态差，水流空化数偏低，底空腔偏小，水流掺气能力不足。针对存在的这些问题，提出了两种体型改进方案。(3)对两种改进方案进行了常压模型试验研究。观测测量的结果包括水流流态，水翅范围高度，底侧空腔长度，清水区范围，底板侧墙压力分布，水流空化数及掺气性能等。通过对比分析，探讨了各体型变化要素对突扩突跌段水力特性的影响，特别是侧扩宽度对侧墙压力分布、清水区范围及水流流态的影响，从冲击反射压力最小的角度提出了最不利侧扩宽度的概念。在局部开启试验中，开度0.75时流态很差，而0.5开度时，侧墙存在一定范围的负压域，且空化数较小，表明特定的局部开启工况可能使特定流动要素处于最不利的情况。(4)针对弧形闸门突扩突跌段侧墙存在清水区易于发生空蚀破坏的问题，通过减压模型试验对其空化特性进行了研究。通过空化噪声谱声压级差及噪声能量分析得出的两种改进方案的空化特性与常压试验以水流空化数为判据的结果并不完全对应，表明侧墙冲击反射区内的空化机理比较复杂，对其进行了初步的探讨。(5)研究了多级水位、不同开度及存在多种尺度凸体时侧墙的空化特性。结果表明，对于侧扩Δb=0.5m方案，设计水位为最不利水位。对于侧扩Δb=0.8m方案，正常水位为最不利水位，且在闸门0.5开度时，最易于发生空化。壁面存在凸体时水流噪声谱声压级和相对噪声能量大幅增加，当凸体高度超过0.8cm时，各级水位下水流均发生空化或初生空化，表明侧墙空化特性对不平整度比较敏感。(6)对有压泄洪洞弧形闸门突扩突跌出口段三维流动进行了数值模拟，获得了空腔形态、侧墙水翅、压力分布等参数，探讨了空腔冲击点涡旋对气流的吸卷作用，并研究了空腔的回水特性。数值模拟表明在底板和侧墙的冲击点附近会各形成一个强的涡旋区，在底板该涡旋卷入空气，形成下游的掺气水流，在侧墙该涡旋可能成为诱发空化的空化源。通过与模型试验数据对比，分析了数学模型对有压泄洪洞弧形闸门突跌突扩出口段复杂流场的预测能力。更多还原

【Abstract】 The chute or tunnel spillway is most often used water discharge structure in hydropower projects, along which the flow is usual not aligned with the general direction of the flow in the reservoir owing to the limit of terrain. This may lead to transverse gradient over free water surface, and even strong vortex. If the action reach to the supercritical flow section downstream discharge chute, there may produce shock wave in water surface, which may directly threat the safety of discharge structure itself and even dam.Eccentric hinge and side expansion water seal for arc gate both require abrupt enlarging in gate seat and bottom, so combining gate seal and aeration devices effectively. After the flow leaving from gate seat and ejecting out from pressure tunnel, it diffuses along the horizontal and vertical directions, and forms side cavities with side wall and bottom cavities with bottom. The bottom cavities and side cavities mutually complement, turning into effective aerator which protects the rigid wall in downstream. But the water-wing generated from impaction between flow and sidewall, and the low pressure generated from impact echo may worsen the flow pattern, even lead to cavitation.In this thesis, the complex flow in control sections of both bi-tunnel spillways and abrupt enlarging and abrupt falling segment of arc gate are investigated with numerical simulation and model test. The main contents of the studies and achievements are as following:(1) The fractional volume of fluid model and the k-e turbulence model are used to study the three dimensional free water surface flows over bi-tunnel spillway. Obtained hydraulic parameters include velocities and distribution of pressure, etc. The simulation also reveals the distort form of free water surface in weir crest. In order to improving inlet flow pattern, eliminating large negative pressure in weir crest and balancing the flow rate distribution between two channels, numerical simulation and model test are combined to get prospective inlet configuration and overflow weir shape, and a new type of water guide wall is proposed.(2) The hydraulic characteristics in abrupt enlarging and abrupt falling segment of arc gate are studied by means of model tests. The experiment shows that negative pressure exists in the roof of pressure tunnel outlet and open channel segment, strong water-wing on sidewall, unstable flow in open channel. And also low cavitation number, small bottom cavity and insufficient aeration exist in original design. Aiming at these problems, two schemes for shape optimization are recommended.(3) Experimental results for the two recommended schemes include flow pattern, size of the water-wing, length of bottom cavity, size of un-airflow area, pressure distribution of sidewall and bottom, cavitation number and aeration performance, and so on. The influence of different shape factors on hydrodynamic characteristics of abrupt enlargement and abrupt fall section are analyzed, especially influences of side expansion on pressure distribution of sidewall、size of un-airflow area and flow pattern. From the view of minimum pressure due to jet impact and reflection, unfavorable side expansion width is put forward. Experimental research with partial opening shows that some specific partial opening conditions may result in the worst condition.(4) Because there exists un-airflow area on sidewall which is difficult to be aerated. Cavitation characteristics of abrupt spreading or abrupt falling segment of arc gate is studied by mean of vacuum model test. It shows that cavitation mechanism in sidewall impacting reflection area is complex.(5) Cavitation characteristics of sidewall under different water level and different similarity vacuum pressures are discussed for different roughness and smooth wall. Under specific water level or specific opening, flow cavitation performance may be the worst, and noise pressure level and relative noise energy increase quickly. When the height of convex bodies exceeds certain value, cavitation may occur under all different water levels.(6) The numerical simulation was used to investigate three dimensional flow of outlet of abrupt spreading or abrupt falling segment of arc gate. The simulation found cavity structure, water-wing of sidewall and pressure distribution. Influence of vortex in jet impact region on aeration is discussed. The result shows that the jet can form a strong vortex at impact point both on bed and side walls. On the bed, the vortex suck into air, on the side, the vortex may become a source of cavation.更多还原