波状水跃和波状涌潮的分析

推导了涌潮中尺度方程，并利用此方程，分析水跃和涌潮的性质，对于水跃和涌潮，色散与耗散两种效应强弱的价值依赖于Ｆｒｏｕｄｅ数的函数，存在着两个临界值，当跃前Ｆｒｏｕｄｅ数大于第一个临界值时，水跃和涌潮从单调形态转化为波动形态，随后，波陡随Ｆｒｏｕｄｅ数增大，当Ｆｒｏｕｄｅ数大于第二个临界值时，自由表面破碎，波状涌潮转化为强涌潮，对于涌潮，绝对流速，即落潮流速，对色散波的周期，波长与振幅也有影响。数值     

二维兴波水翼水动力预报的涡分布法

本文用奇点面分布法预报二维自由面边界下水翼的水动力特性。采用线性化的自由面边界条件。水翼表面划分为若干单元，每个单元上布置线性分布的涡，并在其中点满足Ｎｅｕｍａｎｎ型物面边界条件。与试验结果比较表明，计算结果是合理的，本计算方法能显示二维兴波水翼水动力特性与Ｆｒｏｕｄｅ数，相对浸深和攻角的关系。     

三维明渠流动数值模型

本文对经典的SIMPLE方法进行了改进,在模拟具有自由表面的湍流问题时,摒弃了对自由表面常作的“刚盖”假定。通过求解k-ε模式闭合的三维雷诺方程及自由表面运动方程,得到了渠道槽沟区水流速度、涡粘性系数、湍流切应力、湍动能的分布规律和自由水面位置的变化规律,计算结果与实测值十分吻合。     

关于明渠水充的六区流态

用下临界Ｒｅｙｎｏｌｄｓ数、上临界Ｒｅｙｎｏｌｄｓ数、临界Ｆｒｏｕｄｅ数将明渠水流的流态划分为六区，即：缓层流、缓过渡流、缓紊流、急层流、急过渡流、急紊流，提出了六区流态划分图。并对明渠流与管流采用统一的流速公式问题，提出了看法。     

关于明渠水流的六区流态

用下临界Ｒｅｙｎｏｌｄｓ数、上临界Ｒｅｙｎｏｌｄｓ数、临界Ｆｒｏｕｄｅ数将明渠水流的流态划分为六区，即：缓层流、缓过渡流、缓紊流、急层流、急过渡流、急紊流，提出了六区流态划分图。并对明渠流与管流采用统一的流速公式问题，提出了看法。     

数值模拟二维气泡在粘性液体中上升运动的边界积分方法

本文在考虑界面张力的条件下，和边界层方法马液体粘性对无粘势流的影响化为修改势流在自由面上边界条件的办法，导出了数值模拟二维气泡在粘性液体中上升和变形的边界积分方法。边界层近似的误差为Ｏ（δ＾３）＝Ｏ（Ｒｅ＾－３／２）。数值模拟结果显示，在大气泡（大Ｒｅｙｎｏｌｄｓ数）情形的影响很小。随着气泡尺寸的减小，表面张力和粘性的影响都增强，但与表面张力相比，粘性的影响处于比较次要的地位。     

旋涡排砂在阿勒泰市东戈壁引水干渠中的应用

旋涡排砂技术是解决渠道泥砂淤积又一新技术，该技术采用不对称结构设计旋池来适应池内不对称流态，在旋池内设置了稳流环，形成内涡与外环，内涡中的水流由稳流环的底部从外环进入，增加了自由涡与外环的底部流速，对泥砂的运移十分有利。稳流环的另一个作用是在旋池内形成凸岸，有利于泥砂沉积。     

混合对流绕圆柱涡旋脱落及对传热影响的数值研究

利用本文作者改进的关于流函数一涡量方向的数值求解方法，模拟了混合对流绕圆柱涡旋脱落及对传热的影响，得到了雷诺数Ｒｅ与格拉肖夫数Ｇｒ双重作用下圆柱尾迹涡型转变的规律，并数值研究耻存在小扰动的自由来流、圆柱旋转（γ）及浮力与来流成不同角度（δ）等因素对旋涡脱落，对传热的影响。除Ｒｅ数处，δ，Ｇｒ数对尾涡流型及传热产生较大影响，可利用这些参数来控制绕流流动及强化传热作用。     

三维方腔拖曳流的数值模拟

本文推导出一种适用于定常和不定常粘性不可压缩Navier-Stokes方程的分裂步方法。采用Taylor-Galerkin有限元格式进行求解，对有限元等式中关于速度的时间项进行三点向后差分，深入考虑粘性不可压缩流Navier-Stokes方程中对流项的作用，利用二阶Taylor展开完成时间项向空间项的转化，采用张量分析的方法推导了N-S方程分裂步方法的有限元离散格式，并采用低Reynolds数三维方腔拖曳粘性流^[23][24]作为基本算例，检验了这种分裂步方法的稳定性和有效性，同时与大涡模拟相结合对Reynolds数为10000的三维方腔拖曳湍流流场进行了相关的分析，进一步揭示了方腔回流运动的非定常非对称性、流动结构表现为竖轴环流与立面环流相叠加、流速沿垂线分布相对均匀等流动规律，显示了该方法与大涡模拟相结合能够有效地捕捉涡系及其时变过程。     

带自由表面的后向台阶起动流的流场模拟

对雷诺数Re=1350带自由表面的后向台阶起动流进行数值模拟,得到其自由表面、再附着长度以及台阶后分离涡涡心位置随时间变化的规律,并进一步讨论了自由表面的波动和台阶后大尺度涡结构的产生、发展及溃灭的过程对再附着长度的影响。     

分层流体中冰脊拖曳力的数值模拟研究

冰脊在分层流体表面的漂移运动会在内界面激发出内波,内波又会对冰脊的运动、堆积产生重要影响。利用湍流模型对冰脊在分层流体中的运行过程进行了数值模拟研究,并与已有物理模型实验结果做了比较,冰脊拖曳力和内波界面的数值模拟结果与物理实验结果吻合良好。当流场属于跨临界区时,内波的产生使冰脊拖曳力随弗劳德数Fr先增大后减小,冰脊拖曳系数随Fr的变化规律类似。当流场属于超临界区时,拖曳力随Fr增大而增大,拖曳系数不再随弗劳德数变化。当内波波峰达到最高点的时候,冰脊拖曳力达到一个峰值。     

冷却池试验模型律探讨

我国现用的冷却池模型试验方法和模型与原体的水温换算关系，是由系统的总体热平衡关系求得的，没有考虑水流内部的运动关系。本文用常规的方法，从运动方程出发推导模型试验相似律，考虑了水流的运动结构；包括温排水的近区和远区，分层和不分层等差别。提出模型中弗劳德数和密度弗劳德数必须同时与原型相等。在原体气温和试验室的气温相差较大时，必须考虑水的密度随水温的变化。因此本文提出的原型和模型水温的换算方法，将和现有方法有明显差别。     

Two-phase SPH simulation of vertical water entry of a two-dimensional structure

In view of the fact that the SPH model is easy to handle the flows with the free surface of large deformation, a 2-D flow induced by vertical water entry of a 2-D structure is simulated using the two-phase SPH model. The local pressure of the boundary particles is obtained by pressure of the fluid particles nearby through a modified kernel approximation. To evaluate the accuracy of the method, water entry of a 2-D symmetric wedge with fixed separation point of the free surface on the wedge surface is simulated. The pressure distribution of the wedge at the initial stage agrees well with the analytical results available. Evolution of the free surface and the air flow in the cavity induced by the water entry are obtained. A higher speed air jet is found at the neck of the cavity when the neck of the cavity becomes smaller. For the case of a horizontal cylinder entering the water with an unknown separation point of flow on the model surface, the early stage of the water entry is simulated for the rigid body with different density. Evolution of the free surface deformation of the half-buoyant cylinder and neutrally buoyant cylinder water entry is compared with the experimental data. The effects of the density ratio and Froude number on the pinch-off of the cavity are discussed. It is found that the pinch-off time remains almost constant for different density ratio and Froude number. Meanwhile, for a given Froude number, the dimensionless pinch-off depth and the location of the cylinder at the time of pinch-off increase with the density ratio. Further, for a given density ratio, these two parameters increase with the Froude number and, however, the relative cavity shape appears to be a self-similar shape when Fr ?8.35.     

孤立波作用下边界层的模拟与分析

孤立波作用下的边界层内的剪切力以及涡量变化对海啸传播和海底地形塑造十分重要。本文基于多区域谱方法,利用直接模拟(DNS)数值模型,对在具有矩形断面的U形水洞内的孤立波下的边界层流动进行了模拟。将数值模拟结果与解析解以及试验结果进行了对比,发现数值结果与后两者吻合得较好。模拟结果显示,在低雷诺数下,扰动不会改变流态,而随着雷诺数的增大,流态会变得十分复杂。中等雷诺数情况下,边界层内会产生正向的涡,并进行稳定的传播。在较高雷诺数情况下,流动进入层流向紊流发展的过渡期,此时边界层内会产生正涡以及负涡,并会在水深方向进行不规则运动。     

Free-surface flow past a submerged cylinder

This study employs a Lagrangian frame numerical method to investigate two-dimensional free-surface flow induced by a submerged moving cylinder. This method combines the advantages of vortex methods and boundary integral methods, and is capable of capturing the complex motion of free surface and vortices. A series of computations are performed to investigate the effects of Froude number, the depth of submergence and still water depth on the flow motion. Free surface deformation, wake vortex and hydrodynamic forces are studied.

     

Circulation characteristics of horseshoe vortex in scour region around circular piers

This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter (ADV). Velocity vector plots and vorticity contours of the flow field on the upstream plane of symmetry (y = 0 cm) and on the planes ±3 cm away from the plane of symmetry (y = ±3 cm) are presented. The vorticity and circulation of the horseshoe vortices were determined using the forward difference technique and Stokes theorem, respectively. The results show that the magnitudes of circulations are similar on the planes y = 3 cm and y = -3 cm, which are less than those on the plane y = 0 cm. The circulation decreases with the increase of flow shallowness, and increases with the densimetric Froude number. It also increases with the pier Reynolds number at a constant densimetric Froude number, or at a constant flow shallowness. The relative vortex strength (dimensionless circulation) decreases with the increase of the pier Reynolds number. Some empirical equations are proposed based on the results. The predicted circulation values with these equations match the measured data, which indicates that these equations can be used to estimate the circulation in future studies.     

STUDY OF INTERACTION BETWEEN VORTICES AND A FREE SURFACE PART Ⅱ：INTERACTION OF DOUBLE VISCOUS VORTEX DIPOLES WITH A FREE SURFACE

ＳＴＵＤＹＯＦＩＮＴＥＲＡＣＴＩＯＮＢＥＴＷＥＥＮＶＯＲＴＩＣＥＳＡＮＤＡＦＲＥＥＳＵＲＦＡＣＥＰＡＲＴⅡ：ＩＮＴＥＲＡＣＴＩＯＮＯＦＤＯＵＢＬＥＶＩＳＣＯＵＳ　ＶＯＲＴＥＸＤＩＰＯＬＥＳＷＩＴＨＡＦＲＥＥＳＵＲＦＡＣＥ￥ＷｕＣｈｕｉ－ｊｉｅ；Ｔａｎ...     

Surface and interfacial gravity waves due to a disturbance steadily moving in a two-layer inviscid fluid

The generation and interaction of surface and interfacial gravity waves due to an submerged source moving in a two-layer fluid are investigated analytically for two-dimensional cases. The fluid is assumed to be inviscid and incompressible. The density of each of the two layers is constant. Two different boundary conditions are considered for the upper surface. The upper fluid of finite depth is bounded above by a rigid lid or a free surface. Based on the assumption of small-amplitude waves, a linear system is established. The integral solutions for the free-surface and interfacial elevations are obtained by means of the Fourier transform. Then the corresponding asymptotic representations are derived for far-field waves by the residue theorem. The critical Froude numbers for the existence of far-field waves are derived for the two-layer system bounded above by a rigid lid or a free surface. The effect of different upper boundary conditions on the wave generation are discussed.

     

不可压缩旋转涡对的流噪声计算研究

相隔一定距离的两个同向旋涡相互诱导而形成绕中点旋转的涡对,进而诱发流噪声。该文基于不可压缩流场提供的非稳态流动信息,采用黏声分离法研究水流场中旋转涡对的声学特性。计算结果同理论值进行比较,并探讨了计算条件对计算稳定性和准确性的影响。计算结果表明:在选取合适的计算参数(人工阻尼、网格尺寸和时间步长)的情况下,黏声分离法方法适用于预测水流噪声。对不可压缩旋转涡对的声场特性进行分析,得到旋转涡对声压图案类似四极子,在远场接近圆柱波;随着旋转马赫数的增加,声压级增大。