A Multiscale-Domain Decomposition Method for High Reynolds Number Flows

The high Reynolds number flow contains a wide range of length and time scales, and the flow domain can be divided into several sub-domains with different characteristic scales. In some sub-domains, the viscosity dissipation scale can only be considered in a certain direction; in some sub-domains, the viscosity dissipation scales need to be considered in all directions; in some sub-domains, the viscosity dissipation scales are unnecessary to be considered at all. For laminar boundary layer region, the characteristic length scales in the streamwise and normal directions are L and L Re-1/ 2 , respectively. The characteristic length scale and the velocity scale in the outer region of the boundary layer are L and U, respectively. In the neighborhood region of the separated point, the length scale l<

Numerical Analyses of Transonic Fluid/Structure interaction in Aircraft Engineering

Through the coupling between aerodynamic and structural governing equations, a fully implicit multiblock aeroelastic solver was developed for transonic fluid/stricture interaction. The Navier-Stokes fluid equations are solved based on LU-SGS (lower-upper symmetric Gauss-Seidel) Time-marching subiteration scheme and HLLEW (Harten-Lax-van Leer-Einfeldt-Wada) spacing discretization scheme and the same subiteration formulation is applied directly to the structural equations of motion in generalized coordinates. Transfinite interpolation (TFI) is used for the grid deformation of blocks neighboring the flexible surfaces. The infinite plate spline (IPS) and the principal of virtual work are utilized for the data transformation between fluid and structure. The developed code was fort validated through the comparison of experimental and computational results for the AGARD 445.6 standard aeroelastic wing. In the subsonic and transonic range, the calculated flutter speeds and frequencies agree well with experimental data, however, in the supersonic range, the present calculation overpredicts the experimental flutter points similar to other computations. Then the flutter character of a complete aircraft configuration is analyzed through the calculation of the change of structural stiffness. Finally, the phenomenon of aileron buzz is simulated for the weakened model of a supersonic transport wing/body model at Mach numbers of 0.98 and l.05. The calculated unsteady flow shows, on the upper surface, the shock wave becomes stronger as the aileron deflects downward, and the flow behaves just contrary on the lower surface of the wing. Corresponding to general theoretical analysis, the flow instability referred to as aileron buzz is induced by a stronger shock alternately moving on the upper and lower surfaces of wing. For the rigid structural model, the flow is stable at all calculated Mach numbers as observed in experiment

Information Preservation (IP) Method in Simulation

This paper reviews firstly methods for treating low speed rarefied gas flows: the linearised Boltzmann equation, the Lattice Boltzmann method (LBM), the Navier-Stokes equation plus slip boundary conditions and the DSMC method, and discusses the difficulties in simulating low speed transitional MEMS flows, especially the internal flows. In particular, the present version of the LBM is shown unfeasible for simulation of MEMS flow in transitional regime. The information preservation (IP) method overcomes the difficulty of the statistical simulation caused by the small information to noise ratio for low speed flows by preserving the average information of the enormous number of molecules a simulated molecule represents. A kind of validation of the method is given in this paper. The specificities of the internal flows in MEMS, i.e. the low speed and the large length to width ratio, result in the problem of elliptic nature of the necessity to regulate the inlet and outlet boundary conditions that influence each other. Through the example of the IP calculation of the microchannel (thousands long) flow it is shown that the adoption of the conservative scheme of the mass conservation equation and the super relaxation method resolves this problem successfully. With employment of the same measures the IP method solves the thin film air bearing problem in transitional regime for authentic hard disc write/read head length ( ) and provides pressure distribution in full agreement with the generalized Reynolds equation, while before this the DSMC check of the validity of the Reynolds equation was done only for short ( ) drive head. The author suggests degenerate the Reynolds equation to solve the microchannel flow problem in transitional regime, thus provides a means with merit of strict kinetic theory for testing various methods intending to treat the internal MEMS flows.

Information preservation (IP) method in simulation of internal rarefied gas flows in MEMS

This paper reviews firstly methods for treating low speed rarefied gas flows: the linearised Boltzmann equation, the Lattice Boltzmann method (LBM), the Navier-Stokes equation plus slip boundary conditions and the DSMC method, and discusses the difficulties in simulating low speed transitional MEMS flows, especially the internal flows. In particular, the present version of the LBM is shown unfeasible for simulation of MEMS flow in transitional regime. The information preservation (IP) method overcomes the difficulty of the statistical simulation caused by the small information to noise ratio for low speed flows by preserving the average information of the enormous number of molecules a simulated molecule represents. A kind of validation of the method is given in this paper. The specificities of the internal flows in MEMS, i.e. the low speed and the large length to width ratio, result in the problem of elliptic nature of the necessity to regulate the inlet and outlet boundary conditions that influence each other. Through the example of the IP calculation of the microchannel (thousands m ? long) flow it is shown that the adoption of the conservative scheme of the mass conservation equation and the super relaxation method resolves this problem successfully. With employment of the same measures the IP method solves the thin film air bearing problem in transitional regime for authentic hard disc write/read head length ( 1000 L m ? = ) and provides pressure distribution in full agreement with the generalized Reynolds equation, while before this the DSMC check of the validity of the Reynolds equation was done only for short ( 5 L m ? = ) drive head. The author suggests degenerate the Reynolds equation to solve the microchannel flow problem in transitional regime, thus provides a means with merit of strict kinetic theory for testing various methods intending to treat the internal MEMS flows.

Monte Carlo Modeling of Micro Scale Gas Flows

An information preservation (IP) method has been used to simulate many micro scale gas flows. It may efficiently reduce the statistical scatter inherent in conventional particle approaches such as the direct simulation Monte Carlo (DSMC) method. This paper reviews applications of IP to some benchmark problems. Comparison of the IP results with those given by experiment, DSMC, and the linearized Boltzmann equation, as well as the Navier-Stokes equations with a slip boundary condition, and the lattice Boltzmann equation, shows that the IP method is applicable to micro scale gas flows over the entire flow regime from continuum to free molecular.

Numerical Study of Heat Transfer Mechanism in Turbulent Supercritical CO2 Channel Flow

Direct numerical simulation (DNS) of supercritical CO2 turbulent channel flow has been performed to investigate the heat transfer mechanism of supercritical fluid. In the present DNS, full compressible Navier-Stokes equations and Peng-Robison state equation are solved. Due to effects of the mean density variation in the wall normal direction, mean velocity in the cooling region becomes high compared with that in the heating region. The mean width between high-and low-speed streaks near the wall decreases in the cooling region, which means that turbulence in the cooling region is enhanced and lots of fine scale eddies are created due to the local high Reynolds number effects. From the turbulent kinetic energy budget, it is found that compressibility effects related with pressure fluctuation and dilatation of velocity fluctuation can be ignored even for supercritical condition. However, the effect of density fluctuation on turbulent kinetic energy cannot be ignored. In the cooling region, low kinematic viscosity and high thermal conductivity in the low speed streaks modify fine scale structure and turbulent transport of temperature, which results in high Nusselt number in the cooling condition of the supercritical CO2.

Receptivity to free-stream disturbance waves for blunt cone axial symmetry hypersonic boundary layer

Based on high-order compact upwind scheme, a high-order shock-fitting finite difference scheme is studied to simulate the generation of boundary layer disturbance waves due to free-stream waves. Both steady and unsteady flow solutions of the receptivity problem are obtained by resolving the full Navier-Stokes equations. The interactions of bow-shock and free-stream disturbance are researched. Direct numerical simulation (DNS) of receptivity to free-stream disturbances for blunt cone hypersonic boundary layers is performed.

Characteristics of flow fields induced by interfacial waves in two-layer fluid

When designing deep ocean structures, it is necessary to estimate the effects of internal waves on the platform and auxiliary parts such as tension leg, riser and mooring lines. Up to now, only a few studies are concerned with the internal wave velocity fields. By using the most representative two-layer model, we have analyzed the behavior of velocity field induced by interfacial wave in the present paper. We find that there may exist velocity shear of fluid particles in the upper and lower layers so that any structures in the ocean are subjected to shear force nearby the interface. In the meantime, the magnitude of velocity for long internal wave appears spatially uniform in the respective layer although they still decay exponentially. Finally, the temporal variation for Stokes and solitary waves are shown to be of periodical and pulse type.

Molecular dynamics simulation of adhesion forces in a dipalmitoylphosphatidylcholine membrane

Adhesion forces of Dipalmitoylphosphatidylcholine ( DPPC) membrane in the gel phase are investigated by molecular dynamics ( MD) simulation. In the simulations, individual DPPC molecules are pulled out of DPPC membranes with different rates and we get the maximum adhesion forces of DPPC membrane. We find that the maximum adhesion forces increase with pull rate, from about 400 to 700 pN when pull rates are from 0.001 to 0.03 nm/ps. We analyze the relationship between pull rate and adhesion forces of different origins using Brownian dynamics and notice that viscosity of solvent plays an important role in adhesion forces. Then we simulate the motion of a single DPPC molecule in solvent and it elucidates that the maximum drag force is almost linear with respect to the pull rate. We use Stokes' relation to describe the motion of a single DPPC molecule and deduce the effective length of a DPPC molecule. Conformational analyses indicate that the free energy variation of a DPPC molecule inside and outside of the DPPC membrane is an essential part of adhesion energy.

分岔管路内油水两相流动的研究

分岔管路大量存在于石油行业的输送管网中,油水两相流在分岔管路内的流动特性将对流程控制、动力匹配及下游处理设施产生显著的影响。对分岔管路内的油水两相流动进行了实验研究,采用不可压缩Nayier-Stokes方程结合双流体模型和混合k-ε模型对分岔管路内的油水两相流动进行了数值模拟,获得了初步的结果。计算表明,数值模拟能够较好地反映分岔管路内的油水两相流动,为工程设计提供参考。

不可压和可压缩湍流的多尺度方程组

基于湍流尺度间相互作用的近程特征,作者们曾建议湍流平均分析的多尺度方法。本文进一步研讨这一问题。从空间平均不可压Navier-Stokes方程组,动量和能量湍流交换定义式出发,论证了尺度间相互作用的近程特征,给出近程尺度范围估计,获得近程涡应力,近程涡热传导等的积分和微分近似式;引入尺度间共振相互作用的概念,获得共振涡应力,共振涡热传导等的微分近似式;给出二尺度和三尺度方程组,它们都是不包含经验常数的近似封闭方程组,讨论了多尺度方程组的性质及其与传统大涡模拟方程组的区别;考察了二尺度方程组计算不可压槽道和平面混合层流动三维时间演化的数值结果。对可压缩湍流,通过类似于不可压湍流多尺度方法的处理,给出了可压湍流多尺度(二尺度和三尺度)方程组。可压湍流多尺度方程也含有Favre平均量和物理平均量之间的一组非线性关系式。这些关

翼身组合体跨音速副翼翁鸣现象数值模拟(英文)

本文发展多块网格的生成技术和网格变形方法,通过耦合求解三维薄层Navier-Stokes方程与结构运动方程数值模拟翼身组合体跨音速副翼翁鸣现象。整个翼身组合体网格分成30块子区,子区之间的流场数据传递通过两层虚拟网格单元来完成。在每一步实时推进计算中,通过内迭代使整个耦合计算的时间精度达到二阶。计算中仅考虑了机翼与副翼的结构变形,在整个计算中副翼网格没有单独分区,而是在主翼与副翼之间引进了“剪刀差”网格,所以这种方法只适合于副翼小变形的情况,但从副翼随时间的变形趋势,可以大致推断是否有副翼翁鸣发生。数值模拟结果表明:对副翼刚性较强的结构模型,在小扰动作用下,副翼结构变形的振幅随时间变化减小,最后结构恢复到平衡态。但对副翼刚性较弱的结构模型,在马赫数0.98与1.05时,副翼结构变形的振幅随时间发展迅速增大,呈现副翼翁鸣现象

NS方法数值预测跨音速气动颤振边界(英文)

本文通过耦合求解三维薄层Navier-Stokes方程与结构运动方程数值模拟了跨音速气动颤振现象。其中,流动控制方程的求解采用具有三阶精度的HLLEW(Harten-Lax-vanLeer-EinfeldtWada)迎风TVD空间离散格式和LU-SGS内迭代时间推进方法,同样的内迭代方法用于结构运动方程的求解。在每一步实时推进计算中,通过内迭代,使整个耦合计算的时间精度达到二阶。针对每一时间步的结构变形,发展了一种自适应网格变形方法,在中等结构变形的情况下,该方法能保证变形后的网格具有原网格的质量。为检验发展的跨音速气动颤振计算程序,对一标准气动弹性机翼的跨音速气动弹性边界进行了计算,获得了与实验一致的结果。另外,还详细研究了网格数、时间步长及内迭代步数对气动颤振计算的影响。

微重力流体力学

目录

前言
第一章 微重力流体科学概论
一、微重力科学与微重力流体科学
1、微重力环境
2、重力的影响
3、微重力流体科学的发展
二、微重力流体力学概述
1、对流
2、扩散及输运现象
3、液滴和气泡动力学
4、多相流过程
5、残余重力效应
6、其他流体力学问题
三、微重力物理化学概述
1、临界现象
2、燃烧
3、分散体悬浮系统
4、晶体生长的物理化学问题
四、微重力流体科学的研究途径
1、微重力研究的一般途径
2、微重力实验手段
参考文献
第二章 基本方程组和流体运动特性
一、引言
二、连续性方程和迁移方程
三、动量方程
1、流体的粘性——Reynolds应力
2、动量守恒定律
3、Navier-Stokes方程
四、能量方程
1、总能量方程
2、动能方程
3、内能方程
4、粘性耗散函数
5、Fourier定律及另外二种形式的能量方程
6、不可压流体的导热方程
五、Newton流体的运动方程组及定解条件
1、基本方程组和适定性
2、定解条件
六、Boussinesq近似及适用范围
七、相似律和无量纲参数
1、利用Buckinghan〓定理导出相似参数
2、微重力流体力学的有关物理量和无量纲参数
参考文献
第三章 毛细现象以及界面的平衡和稳定
一、引言
二、表面张力的物理描述
三、液体射流的表面不稳定
1、基本方程组和基态
2、小扰动的线性化方程
3、本征值方程及其解
四、等温条件下液桥的平衡位型和稳定
1、表面张力作用下的平衡条件
2、毛细稳定性
3、旋转稳定性
第五章 液桥的流体动力学稳定理论
1、基本假设和液桥的平衡条件
2、稳定问题的数学提法
3、液桥的Liapunov稳定理论
4、特殊情形（Ω〓=μ=0）以及纯半波不稳定（n=1，m=1）
5、小扰动方程的变分方程
6、小Weber数和大Reynolds数情形的不稳定发展率
7、液桥微重力实验的结果的分析
8、讨论和结论
参考文献
第四章 对流和扩散
一、Pearson对流
1、自由面不变形时的小扰动分析
2、自由面可变形情形
3、非线性理论
4、多层不混溶液体系统
二、热毛细对流
1、矩形容器中的热毛细对流
2、柱形液桥的热毛细对流
3、半浮区液桥热毛细对流的数值模拟
4、薄层液体的热毛细对流
三、热毛细振荡对流的实验研究
1、液桥内部的温度振荡
2、热毛细对流的表面振荡
3、综合测量
四、热毛细对流的振荡机理
1、热流体波不稳定性
2、表面波不稳定性
3、有限高度液桥的线性不稳定性
4、三维不定常数值模拟
5、重力的影响
6、一种非稳定性理论
7、关于振荡的激发机制
参考文献
第五章 液滴动力学
一、等温液滴动力学
1、球形液滴的振荡
2、不混溶液体中球形液滴的振荡
3、弱非线性理论
4、实验模拟
二、非等温液滴的Marangoni迁移
1、定常线性化理论（小Reynolds数，小Marangoni数）
2、非线性理论
3、实验结果
三、液滴和气泡的相互作用
1、双气泡的轴对称理论
2、多液滴的轴对称理论
四、旋转液滴的演化序列和分叉理论
1、旋转液滴的演化
2、旋转液滴的Thomson-Tait稳定准则
3、长期稳定性和动力稳定性
4、长期稳定性真实性的实验证明
5、结论
参考文献
第六章 微重力材料流体力学
一、晶体生长过程
二、纯扩散过程
1、一维扩散过程
2、二维扩散过程
3、固-液界面弯曲对径向分凝的影响
三、浮区晶体生长
1、浮区的热毛细对流
2、浮区的熔质毛细对流
3、浮区对流的振荡特征（小Prandtl数对流）
4、耦合过程
四、溶液晶体生长
1、溶液晶体生长的相变界面过程
2、一维纯扩散过程
3、准定常溶液晶体生长过程
4、不定常溶液生长过程
五、气相晶体生长
1、气相晶体生长过程
2、一维模型
3、物理气相输运中的对流效应
4、化学气相沉积（CVD）过程
参考文献

计算流体力学