【作者】 李冰冻；

【导师】 李克锋；

【作者基本信息】 四川大学 ， 水力学及河流动力学， 2003， 硕士

【摘要】 丁坝是主要的航道整治建筑物之一。修建丁坝可束水归槽，保护岸堤，但也会带来分离、回流等一系列复杂的流动现象。研究丁坝对水流的影响规律以及丁坝附近水流的流动结构对于航道整治建筑物的设计具有十分重要的意义。本文通过模型实验和数值模拟相结合的研究方法，在整治河段一维水面曲线计算，单丁坝绕流数值模拟，紊流数学模型在航道整治工程中的应用以及丁坝群附近水流的三维流动特性等方面做了一些初步研究。 首先进行了单丁坝水槽实验，采用测压管和旋浆流速仪对实验水槽中水流的水位以及流速场进行了详细的测量。分析了丁坝附近水位在纵横向上的变化规律。实测水位资料表明水流纵横向比降大的区域位于丁坝上下游附近，在丁坝的上游出现壅水，下游存在有收缩区和恢复区，离丁坝越远纵横向水位的变幅越小。 然后根据天然河流横断面流速分布公式，推导了能量方程中动能修正系数α的计算公式。动能修正系数实际上反映了河道横断面流速分布的不均匀性，与断面的水力要素有关，可用谢才系数C来表示，水流所受的阻力越大，边界对其影响也就越大，流速分布愈不均匀，导致动能修正系数增大。 随后结合实测水位资料，通过采用调整局部水头损失系数、扣除回水面积以及壅水公式等不同的水面曲线计算方法对实验水槽一维水面曲线进行计算。计算结果表明，局部水头损失系数并不能完全反映出由于丁坝阻挡所带来的水头损失，而丁坝附近的有效过水面积难以准确地确定，这些导致前两种方法均不能很好地计算出丁坝上游水位的壅高值。而采用壅水公式则能很好地计算出四川大学硕士学位论文丁坝上下游的水位差，从而解决工程应用中丁坝上下游水位的衔接问题。 随后采用标准k一e紊流数学模型，依据水槽试验资料，数值模拟了绕坝和漫坝两种情况下水流的流动过程。实测流速资料和数值模拟结果表明，所选用的紊流数学模型可很好的模拟出由于丁坝阻隔水流所产生的分离、回流等流动现象。丁坝绕流和漫流作用机理非常复杂。水流三维流动特性主要集中在丁坝附近区域.丁坝对下游的影响区域远远大于对上游的影响区域。 最后将标准k一:紊流数学模型应用于实际航道整治工程应用中，引入相应的边界条件，数值模拟了整治河段水流的三维流动过程。模拟结果表明，整治河段水流的流速分布主要受制于河道的平面儿何形态，局部区域航道整治建筑物起主要作用。在河道平面上水流流速基本呈中心流速大，两岸流速小的抛物线型分布。群坝对水流的作用机理与单丁坝的作用机理不相同。整治河段中第一根丁坝对水流的阻挡作用最大。受丁坝阻挡，坝田所在的边滩区域流速很小，泥沙在此淤积:而坝头附近流速较大，通常在此区域形成冲刷，影响丁坝的稳定性。更多还原

【Abstract】 Spur dike is a kind of hydraulic structure that is widely used in channel regulation engineering for controlling the shape of the nature river. Some complex flow characteristics such as separation, circumfluence appears around spur dikes. It is of great importance for the design of channel regulation structure to explore the effect of spur dikes on flow, and to study the flow structure near the spur dike. Through flume experiment and numerical simulation, preliminary work on computation of water surface profile in regulation river reach, numerical simulation of flow with single spur dike in flume, and 3-D numerical solution of flow around spur dikes group are carried out in this paper.The flume experiment with single spur dike is carried out. Water surface profile and velocity field of flow in flume are measured by manometer tube and propeller current meter respectively. Variations of water surface along longitudinal and horizontal direction are analyzed. The experiment data shows that the region with large surface gradients in longitudinal and horizontal direction locates at the vicinity of spur dike. Backwater appear upstream the spur dike, and there exist a recirculation area at the same side downstream the spur dike.Based on the cross-sectional velocity distribution of flow in natural river, computation expression for correction coefficient of kinetic energy is derived. Actually correction coefficient of kinetic energy reflects the non-uniform characteristics of cross-sectional velocity in natural rivers. It is related with hydraulic parameters and can be expressed by Chezy’s coefficient. The larger the resistance of boundary, the more non-uniform the distribution of cross-sectional velocity. Thevalue of correction coefficient of kinetic energy increases as a result.The water surface profiles of flume experiments are computed by three different methods: adjusting the local head loss coefficient, deduction of backwater area, and application of backwater expression. Comparison of water level between measured and computation shows that the local head loss coefficient cannot give head loss by spur dike completely, and the effective area of passage is difficult to be ascertain. For this reason the two methods for water surface profile computation cannot predict the raise of water level upstream the spur dike accurately. Only the method for using backwater expression can predict the variation of water surface near the spur dike very well.Numerical simulations of the flume experiment cases are carried out with the standard k-e turbulence model. Comparison between the numerical results and the measured data shows that it is adequate for the standard k ~ e turbulence model to simulate the complicated flow pattern with the existence of separation and circulation zones. Flow structure near the spur dike is very complicated, and areas with apparent three-dimensional characteristic exist in the vicinity of spur dike.The standard k-e model is adopted to simulate the flow of practical channel regulation projects. The numerical results show that the velocity distribution of flow in the regulation project river reach are mainly controlled by the geometries of natural river. But in local region it is mainly controlled by the regulating structures. The planar velocity is of the parabola distribution. The velocity value in the middle of the river is larger than that of the two banks. The effects of spur dikes group to the flow are different to that of single spur dike. The first one among spur dikes group in regulation river reach has the most important holdback effect than the others. Velocities in regions between upstream and downstream spur dikes are very small, and are often less than the sediment deposit velocity. Silt will deposit there. Velocities around groin head are larger than the scour velocity and scour hole may develop in this area. This would affect the stability of spur dikes.更多还原