圆柱体出水运动的自由面效应及水冢现象分析

以圆柱体为例,研究自由面附近刚性物体的受力状态,分析垂直运动圆柱体出水时的自由面效应以及水冢现象.建立基于势流理论考虑自由面效应的数学模型,并用边界元方法求解该模型.求解过程中考虑非线性自由面运动学以及动力学边界条件.通过求解控制方程以及边界条件,模拟恒速刚性圆柱体出水时的水冢现象及其穿越水冢过程.通过数值解和实验值的比较验证方法的可靠性.分析结构出水时的压力变化、自由液面变形、圆柱体所受的垂向合外力以及流场速度矢量的变化,并展开讨论.结果表明:考虑自由面效应的非线性方法能够更准确地预报自由面附近刚性运动物体的受力特性.     

典型自由面流动问题的SPH-ALE数值模拟

应用基于黎曼解的SPH-ALE方法对两种典型自由面流动问题进行数值模拟,并提出一种一阶核函数修正压力计算方法,通过对临近边界的水粒子压力进行核积分,近似估算固壁边界压力.给出不同时刻的流场压力分布及自由液面演化过程,将计算结果与相关的试验值及数值解进行对比,分析结果表明：SPH-ALE方法较传统SPH方法在流场压力计算精度上有较大的改进,在处理强非线性自由面流动问题时能够达到较高的精度.     

液滴冲击液膜问题的光滑粒子动力学模拟

本文对传统的光滑粒子动力学方法进行了改进．改进的光滑粒子动力学方法对传统粒子方法中的核梯度进行了修正,采用了一种新型的耦合边界条件,添加了表面张力和人工应力的计算程序．应用改进的光滑粒子动力学方法对液滴冲击液膜问题进行了数值模拟．得到了不同时刻液滴内部的压力变化特征,精细地捕捉了不同时刻的自由面,从机理上分析了液滴产生飞溅的条件,探讨了韦伯数,表面张力对液滴冲击液膜问题的影响．计算结果表明,改进光滑粒子动力学方法能够有效地描述液滴冲击液膜的动力学特性和自由表面变化特征,能够得到稳定精度的结果．     

运用VOF模型模拟开敞式水泵吸水池内后台阶流动

开敞式水泵吸水池内流动是具有自由表面的复杂流动.本文利用VOF(Volume of Fluid)模型对开敞式水泵吸水池内的后台阶流动进行了数值模拟,模拟结果与试验数据基本吻合.VOF模型是模拟开敞式水泵吸水池内流动的一种有效方法.     

格子Boltzmann方法模拟双液滴撞击液膜的流动过程

采用单相自由面格子Boltzmann方法中流场计算,自由面条件和表面张力处理方法,研究双液滴撞击液膜的流动过程,实现对垂直间隔的两液滴相继撞击液膜流动过程的模拟.数值结果表明,液滴相继冲击液膜时,液滴间上下距离对液膜状态有很大的影响,液滴间距不同,液膜形状会出现很大差异.数值结果与实验结论定性一致.     

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利用函数及其高阶导数值构造五次插值函数近似网格单元内的真实解,改进数值求解双曲类偏微分方程的CIP数值算法。基于之前的一维高阶CIP数值算法思想,不同于利用时间分裂技术,发展了二维高阶CIP数值算法。改进后的算法具有五阶数值精度和显示格式的优点。     

基于不可压缩光滑粒子动力学的黏性液滴变形过程仿真

应用基于投影算法的不可压缩光滑粒子动力学(incompressible smoothed particle hydrodynamics, ISPH)法对黏性液滴变形过程进行了数值仿真. 对于张力失稳导致的粒子非物理簇集问题, 采用粒子移位技术加以解决. 为了验证本文ISPH 算法的精度和稳定性, 分别模拟了圆形黏性液滴的拉伸变形过程以及方形液滴的旋转变形过程, 得到了不同时刻液滴内部的压力变化特征, 准确地捕捉了液滴自由面演化过程, 并将数值计算结果与文献中的解析解进行了比较.分析结果表明, 基于投影算法的不可压缩光滑粒子动力学方法结合粒子移位技术, 能够有效地模拟黏性液滴变形过程, 可以得到精确和稳定的结果. 关键词： 不可压缩光滑粒子动力学 黏性液滴 自由面流动 数值仿真     

液滴溅落问题的光滑粒子动力学模拟

对传统的光滑粒子动力学方法进行了改进, 改进的光滑粒子动力学方法对传统粒子方法中的核近似式和粒子近似式进行了修正, 采用Riemann 算法求解光滑粒子动力学流体控制方程, 添加了表面张力的计算程序, 考虑了表面张力对液滴溅落的影响. 应用改进的光滑粒子动力学方法对液滴静止状态下冲击液面的飞溅过程进行了数值模拟. 计算结果表明, 改进的光滑粒子动力学方法能够有效地描述液滴溅落液面的动力学特性和自由表面变化特征, 能够得到稳定精度的结果.     

水陆两栖飞机静水面高速滑行性能数值计算与试验分析

针对水陆两栖飞机静水面高速滑行过程的运动响应大、流场强非线性等问题，提出了一种基于传统动网格技术的"状态预估——精确计算"的数值模拟方法:通过求解Reynolds平均N-S方程结合运动方程来模拟飞机静水面滑行时的流场特征和运动特性，数值模拟方法为隐式有限体积法，湍流模型采用k-ω（SST Menter）结合壁函数进行处理，自由液面捕捉采用VOF方法；数值计算时，首先采用粗网格对简化后的飞机在不同航速下的姿态和升沉进行快速预估，再将飞机置于预估状态下进行精确网格划分，最后进行精确数值计算分析.为了验证数值模拟结果的正确性，在物理水池中进行了静水拖曳试验，将数值计算结果与试验结果进行对比分析可得:数值计算与水池试验的流场特征吻合，且阻力、姿态和升沉的计算精度达到90%，验证了数值模拟方法的可行性.      

梯度表面能材料表面上液滴形状的数值模拟

本文建立了固体表面上静止液滴的势能方程,根据能量最小化原理,当系统总势能取得最小值时,液滴将处于平衡状态.采用有限元方法,将初始自由液面离散化,通过曲面上节点的虚拟位移,改变自由液面的拓扑结构,使系统总势能取得最小值,从而得到静止液滴的形状.并应用该方法对均质表面和梯度表面能材料表面上的液滴界面进行了数值模拟,得到了均质材料表面和梯度表面能材料表面上静止液滴的界面形状及分布.     

高阶CIP数值方法及其在相关物理问题中的应用

利用函数的高阶空间导数值构建其高次插值,得到高阶CIP(Constrained Interpolation Profile)数值算法,并在此基础上模拟研究等离子体物理中著名的伏拉索夫-泊松(Vlasov-Poisson)方程相关物理问题.高阶CIP数值方法具有更高数值精度,从而可以在同等精度的情况下减少计算格点数,加速数值计算速度.     

Multi-dimensional conservative semi-Lagrangian method of characteristics CIP for the shallow water equations

A new characteristic approach that guarantees conservative property is proposed and is applied to the shallow water equations. CIP–CSL (Constrained Interpolation Profile/Conservative Semi-Lagrangian) interpolation is applied to the CIP method of characteristics in order to enhance the mass conservation of the numerical result. Although the characteristic formulation is originally derived from non-conservative form, present scheme achieves complete mass conservation by solving mass conservation simultaneously and reflecting conserving mass in interpolation profile. Present method has less height error compared to the CIP method of characteristics by several orders of magnitude. By the enhanced conservation property, present scheme is applicable to nonlinear problem such as shock. Furthermore, application to two dimensions including the Coriolis term is straightforward with directional splitting technique.     

Thermocapillary deformation of a thin locally heated horizontal liquid layer

In this paper, steady thermocapillary flow in a thin horizontal layer of a viscous incompressible liquid with a free surface is considered. An axially symmetric steady problem with a localized thermal action on a horizontal liquid layer with a deformable free surface is solved in a thin-layer approximation. In addition to the thermocapillary effect, the model takes into account the capillary pressure caused by the free surface variable curvature and the convective mechanism of heat transfer in the liquid. Analytical expressions for the velocity vector components as functions of the liquid layer thickness and surface temperature are obtained. The free surface and velocity profiles caused by various kinds of heating are calculated. The influence of convective heat transfer on the flow pattern is analyzed.     

振动斜板上下落液体薄膜的数值模拟

用Galerkin有限元法数值模拟了振动斜板上的下落液体薄膜流动,研究了流场中不同强迫频率和初始扰动频率的影响.结果表明由于它们之间的相互作用,流场中出现低频信号,其在流场中的非线性效应使得表面波发生合并,加速了表面波的发展.对较高的强迫频率,这种效应更明显,且可观察到孤立包的产生.     

Free surface flow between two horizontal concentric cylinders

Results are reported on a combined experimental and numerical investigation of a free surface flow at small Reynolds numbers. The flow is driven by the rotation of the inner of two horizontal concentric cylinders, with an inner to outer radius ratio of 0.43. The outer cylinder is stationary. The annular gap is partially filled, from 0.5 to 0.95 full, with a viscous liquid leaving a free surface. When the fraction of the annular volume filled by liquid is 0.5, a thin liquid film covers the rotating inner cylinder and reenters the liquid pool. For relatively low rotation speeds, the evolution of the film thickness is consistent with the theory for a plate being withdrawn from an infinite liquid pool. The overall liquid flow pattern at this condition consists of two counter-rotating cells: one is around the inner cylinder and the other with weaker circulation rate is in the bottom part of the annulus and nearly symmetric about the vertical axis. With increasing rotation rate, the free surface becomes more deformed, and the dynamics of the stagnation line and the cusp line dividing the cells are tracked as quantitative measures of the interface shape. In addition, the recirculating flow cells lose symmetry and the cusp deforms the free surface severely. A comparison of numerically computed flow which describes the interface by a phase-field method confirms the dynamics of the two cells and the interface deformation. For filling fraction 0.75, the liquid level is slightly above the inner cylinder and a significant decrease in size of the bottom cell with increasing rotation rate is found. For filling fractions approaching unity, the liquid flow consists of one single cell and the surface deformation remains small.     

On calculating the oscillations of a viscous liquid layer over a solid spherical core in terms of the boundary layer theory

The theory of a boundary layer near the periodically oscillating free surface of a spherical viscous liquid layer over a solid core (bottom) is modified. Two boundary layers are considered to adequately describe a liquid viscous flow in the system: one at the free surface of the liquid and the other at the solid bottom. The thicknesses of the boundary layers are estimated, which provide any given discrepancy between an exact solution to the model problem and a solution obtained in the small viscosity approximation. Taking into account the boundary layer near the solid bottom is shown to be significant only for lower oscillation modes. For higher modes, the flow near the core can be considered potential. In the case of lower modes and shallow liquid, the surface and bottom boundary layers overlap and an eddy flow occupies the entire volume of the liquid.     

微通道内不混溶气液两相二氧化碳界面动力学行为的格子Boltzmann研究

将高精度的二氧化碳状态方程与气液两相流格子Boltzmann方法中的伪势模型耦合,研究微通道内二氧化碳气液两相流动的界面动力学行为,包括二氧化碳气泡和液滴的分裂、合并、变形,以及气液两相二氧化碳在演化过程中的质量交换.研究发现：当分裂和合并行为达到平衡,并且两相之间不发生质量交换时流动达到稳态.稳态时的流型主要依赖于表面张力,惯性力,管道的润湿性,以及初始体积分数.当表面张力较大时,微通道内形成的二氧化碳气泡或液滴会收缩成圆形,此时二氧化碳气泡或液滴会堵塞微通道,形成段塞流;随着表面张力的减小,形成的气泡或液滴不容易收缩,在微通道内更容易发生变形,出现泡状流或环状流.当壁面润湿性为强疏水性时,二氧化碳在微通道中的流动为环状流,其它润湿性下,流型为段塞流.体积分数较小时,二氧化碳两相流动的流型为段塞流,体积分数较大时,流型为环状流.