【作者】 张楠；

【导师】 张群峰；

【作者基本信息】 北京交通大学 ， 力学， 2018， 硕士

【摘要】 马蹄涡是平面或曲面与突起物构成的角区流场中的主要流动结构,具有强烈的三维非定常流动特性,常与来流边界层、角区结构物等相互作用,对角区结构安全构成威胁。为了探究角区马蹄涡系的结构特性,研究水位高度、来流速度和自由液面等流动参数对角区马蹄涡系的影响,本文运用计算流体力学软件Fluent,采用基于SST k-ω湍流模型的IDDES方法,对圆柱与平板构成的三维角区流场进行了数值模拟研究。文中首先对不考虑自由液面时,来流水深为0.25m,来流速度为0.673m/s状态下的单相流流场进行数值模拟,划分三种数量的网格,并对这三种不同网格的计算结果进行对比分析,验证了数值方法的准确性,确定了合适的网格数量和网格节点分布,并以此为基础,生成考虑自由表面流动的网格,并完成算例验证。针对不考虑自由液面的单相流和考虑自由液面的两相流,在Re=1.13 X105和2.25X 105的两种雷诺数条件下,分别计算了来流水深为0.1m、0.175m、0.25m和0.325m的共计16种工况。研究发现,在不同流动参数条件下,角区湍流马蹄涡系的振荡具有准周期性,其振荡周期受水深、雷诺数、自由液面等流动参数的影响;对于不考虑自由液面的单相流:来流雷诺数相同时,水深的改变对角区涡系没有产生明显的影响;水深相同时,雷诺数的增大使涡系的振荡频率增大,主涡向下游靠近角区的方向移动,涡的强度增大,涡系作用于圆柱周围床面上的壁面摩擦系数减小;在考虑自由液面的两相流中:相同雷诺数条件下,随水深的增加,角区涡系的振荡频率逐渐增大,涡系中主涡向下游靠近圆柱的区域移动,涡系作用于圆柱上游的床面形成的剪切应力增大;水深相同的工况中,来流雷诺数的增大时,角区涡系的振荡频率减小,主涡向远离圆柱的上游方向移动,涡的强度增大,床面上的壁面摩擦系数减小,但随着水深的增加,雷诺数对角区涡系的影响程度减弱。另外,研究还发现,在相同雷诺数条件下,随着来流水深的增加,自由液面对角区涡系的振荡频率、主涡的位置、涡系作用于床面形成的剪切应力等的影响程度减弱。更多还原

【Abstract】 The horseshoe vortex,which is three-dimensional and unsteady,is the main flow structure in the flow field around the wall-cylinder junction.It often interacts with the boundary layer and the structures in the junction are,poses threats to the safety of the structure of the angular region.In order to explore the characteristics of the horseshoe vortex in the junction area and study the effects of the water depth,velocity,the free surface of flow on the horseshoe vortex system,a wall-cylinder junction model is simulated using the computational fluid dynamics software Fluent and SST k-ω IDDES method.In order to determine the optimal grid node distribution in the junction area,for the first condition,of which the depth h of water is 0.25m and the velocity is 0.673m/s,the single-phase flow fields model without free surface under three kinds of girds have been calculated.In addition,to verify the accuracy of this numerical method,the calculated results of three different kinds of grids are also compared.Based on the obtained optimal grid node distribution and grid quantity,the grid that can capture the free surface has been built.Besides,the feasibility of the calculation method is validated.For the single-phase flow without the free surface and the two-phase flow with the free surface,there are totally 16 conditions with the water depths of 0.1 m,0.175 m,0.25 m,and 0.325 m under Re=1.13×105 and 2.25 ×105 have been simulated.It is indicated that the oscillation of the turbulent horseshoe vortex system in the junction region is quasi-periodic under different flow conditions and its oscillation period is affected by water depth,Reynolds number,and the free surface.In the single-phase flow without the free surface,the water level has no obvious influence on the vortex system in the junction region under the same Reynolds number.Under the same water depth,the oscillation frequency of the vortex system increases with the increase of Reynolds number,besides,the increase of the Reynolds number makes the core of the main vortex move downstream,the vortex intensity of the system increases,but the skin friction coefficient decreases.With the increase of the height of the water level,the oscillation frequency of the vortex system in the junction region increases gradually.In addition,the core of the main vortex gradually moves to the downstream region which is close to the cylinder and the wall shear stress on the bed increases under the same Reynolds number in the two-phase flow considering the free surface.With the increase of the Reynolds number,the oscillation frequency of the vortex system decreases and the core of the main vortex moves away from the cylinder in the upstream direction,the vorticity intensity of the vortex increase,while the skin friction coefficient decreases under the same water depths.The influence of the Reynolds number on the vortex system in the junction region has decreased gradually with the increase of the water depth.In addition,the study found that,the influences of free surface on the oscillation frequency of the vortex system in the junction region,the position of the main vortex,the wall shear stress on the bed gradually decrease with the increase of the water depth when the Reynolds numbers are the same.更多还原