【作者】 李志高；

【导师】 陈刚；

【作者基本信息】 西安理工大学 ， 水力学及河流动力学， 2004， 硕士

【摘要】 自由液面问题在工程实践中大量存在，对自由液面问题的研究具有十分重要的工程价值和学术意义，数值模拟是研究和解决实际工程问题主要的方法之一，由于自由液面的特殊性质，对自由液面的处理在数值模拟中显得尤为困难和重要。本文主要对水利工程中一些涉及自由水面及掺气的流动的数值模拟问题进行研究。 首先回顾了在数值模拟中自由液面问题的处理方法和存在的问题，并对数值计算方法进行了简要的综述，根据自由液面的形状，将自由液面分为相对稳定的自由液面和起伏较大的自由液面。对含有相对稳定的和起伏较大的自由水面的水流问题进行了数值模拟。给出了流动的控制方程，利用刚盖假定法对相对稳定的自由水面进行了简化近似处理，用弹性盖法对起伏较大的自由水面进行了简化近似处理，对控制方程进行了封闭、离散和数值求解。以小孤山水电站枢纽冲砂闸闸门上下游流场为实际算例，对计算结果进行了分析。从计算结果来看，对相对稳定的自由液面采用刚盖假定法处理是适合的，计算得到的速度场、压力场与实际比较吻合，根据数值模拟的结果，对闸门胸墙的体型进行了优化；但对闸后起伏较大的自由水面问题采用弹性盖法处理则存在不满意的地方。 对含有自由水面的水气两相流，采用两流体模型，简要给出了水气两相流的控制方程，并考虑相间作用力的影响，在同位网格下，对方程进行离散，并结合明渠掺气水流进行了数值模拟，对明渠水流的自由水面采用改进的刚盖假定法处理并获西安理工大学硕士学位论文得了较好的结果。根据计算结果，对水气两相流中气泡尺寸对掺气浓度预测结果的影响进行了分析，得到沿程气泡不断上逸，气泡粒径越大，其上逸速度越大，则留在渠底附近的气泡越少的气泡运动规律，提出了掺气槽的设计，除满足掺气量外还应满足掺气粒径要求的工程建议。 用VOF法对自由水面问题进行了初步研究。给出了VOF法的控制方程，利用VOF法对明渠水流、闸后水流进行了数值模拟，计算得到了明渠水流和闸后水流水气界面的形状、含气率的分布，流场的速度场、压力场、紊动能及紊动耗散率分布场，计算结果显示了VOF法对无论是相对稳定的自由水面还是起伏较大的自由水面问题的处理，都显现了其优势。 通过本文对数值模拟中的自由液面问题的研究表明，对闸前相对稳定的自由液面问题可以采用相对简单的方法进行处理，但对于闸后起伏较大的自由液面，则需要采用更精细的自由液面处理方法。更多还原

【Abstract】 Many free fluid surface problems exist in engineering practice, so there is very importance engineering value and academic meaning to make scientific researches on free fluid surface. Numerical simulation is one of the primary method to study and solve engineering problems. Because of special quality of free surface, the disposal of free surface become more difficult and important in numerical simulation. Numerical simulation problems about free water surface and air entrained flows in hydraulic engineering are studied in this paper.First, the solving methods and exiting problems of free surface were reviewed and the numerical simulation methods were also brief summarized. Based on the shapes of free surface, the free surface is divided into a relative stable one and a rather fluctuant one. Water current problems including relative steady and rather fluctuant free surface were simulating numerically. Flow control equations were given, relative steady and rather fluctuant free surface were treated approximately with using rigidity cover assume, at the same time, control equations were closed and discretized and numerically solved. Flow field of upstream and downstream of Xiao gushanwater power station hinge discharge sluice were practical calculated examples. The results were analyzed and showed that rigidity cover assume was fitted to relative steady free surface flow upstream sluice. The velocity field and pressure field from the calculation accord with the fact. Based the results of numerical simulation, the bodily form of sluice parapet is optimized. But the elasticity assume existed dissatisfactory aspects to rather fluctuant free surface flow downstream sluice.To air-water two-phase flow including free surface, the control equations of two-fluid model were briefly listed, and the effect of the interfacial momentum transfer term was considered, then the equations were discretized on collocated grid. The open-channel aerated water flow was numerically simulated and the free surface was treated with improved rigidity cover assume. Based on simulation results which were satisfied, the effect of bubble diameter on entrainment concentration forcast result was analyzed. The bubble moving rule was found which includs the bubble is escaping upwards along the way, the diameter of the bubble is bigger, the velocity upwards is larger and the bladder remaining near channel bottom is smaller. To make best use of the function of the aerator, the demands of enough air entrainment quantity and suitable air bubble diameter are needed to be satisfied.The problems of free surface were dealed with by VOF which is more advanced method. The governing equations were listed and the open-channel flow and sluice upstream flow are simulated by using the method of VOF. From the simulation, the shape of air-water surface, the distributing of gas ratio, the velocity field, pressure field, turbulence momentum and turbulence moment dissipation ratio were gained. The results showed that the advantage was displayed by using method of VOF not only for relative steady water surface but for rather fluctuant one.The study on free surface showed the relative simple methods can be used for relative steady free water surface flows upstream the sluice, but more advanced methods must be adopted to rather fluctuant one downstream the sluice.更多还原