T型管内流动气体中爆轰绕射过程的数值模拟

基于带化学反应的二维Euler方程,对H₂、O₂、Ar体积比为2:1:1的混合气体系统在T型管内的爆轰绕射进行了数值模拟。用二阶附加半隐的Runge-Kutta法和五阶WENO格式分别离散欧拉方程的时间和空间导数项,采用9组分48步基元反应简化模型描述爆轰波在静止系统和流动系统中的传播过程,得到了温度、压力、典型组元H质量分数的分布及数值胞格结构。结果表明:在流动系统中,迎风面上波阵面为斜爆轰结构,静止系统两侧和顺风面上的波阵面为完全解耦的前导激波;在水平管中,波阵面与上下壁面经历一系列马赫碰撞后,最终形成正爆轰;在流动系统中,胞格结构明显向下游偏移;横向爆轰波的产生对爆轰波的再生起到了关键作用。     

氢氧混合气体爆轰波的真实化学反应模型数值模拟

采用高精度的ENO格式和基于基元化学反应的真实化学反应模型求解氢氧混合气体一维爆轰波的精细结构。采用直接起爆方法得到稳定传播的爆轰波 ,计算的爆轰波阵面参数和实验相当符合。对爆轰波反应区化学反应的研究表明 ,参与反应的不同组分具有不同类型的变化特征。网格尺寸影响的研究表明 ,计算结果的精度随着网格尺寸的增加而增加 ,并能保持较好的收敛性。移动网格研究结果表明 ,网格运动速度和爆轰速度接近时 ,两者的相互作用对计算结果产生一定影响。     

应用阵面追踪法对散心爆轰波传播的数值模拟

考虑到爆轰波阵面曲率及化学反应区宽度的作用 ,由修正Hugoniot关系式解析求解了波后状态 ,应用阵面追踪法 (FTM)数值模拟了曲面散心爆轰波的传播。计算给出的散心爆轰波走时及波阵面上物理量都达到了波阵面曲率的一阶精度。     

动态混合网格生成及隐式非定常计算方法

建立了一种基于动态混合网格的非定常数值计算方法. 混合网格由贴体的四边形网格、外场 的多层次矩形网格和中间的三角形网格构成. 当物体运动时，贴体四边形网格随物体运动而 运动，而外场的矩形网格保持静止，中间的三角形网格随之变形；当物体运动位移较大，导 致三角形网格的质量降低，甚至导致网格相交时，在局部重新生成网格. 新网格上的物理量 由旧网格上的物理量插值而得. 为了提高计算效率，采用了双时间步和子迭代相结合的隐式 有限体积格式计算非定常Navier-Stokes方程. 子迭代采用高效的块LU-SGS方法. 利用该 方法数值模拟了NACA0012振荡翼型的无黏和黏性绕流，得到了与实验和他人计算相当一致 的结果.     

基于非结构网格求解二维浅水方程的高精度有限体积方法

采用HLL格式,在三角形非结构网格下采用有限体积离散,建立了求解二维浅水方程的高精度的数值模型.本文采用多维重构和多维限制器的方法来获得高精度的空间格式以及防止非物理振荡的产生,时间离散采用三阶Runge-Kutta法以获得高阶的时间精度.基于三角形网格,底坡源项采用简单的斜底模型离散,为保证计算格式的和谐性,对经典的HLL格式计算的数值通量中的静水压力项进行了修正.算例证明本文提出的方法的和谐性并具有高精度的间断捕捉能力和稳定性.     

粘性及热传导对于爆轰波的影响

对在满足化学当量比的氢氧混合气体中传播的一维和二维连续旋转爆轰波进行了数值模拟,以此检验粘性和热传导对爆轰波发展和结构的影响。模拟分别基于NS和Euler控制方程,采用二步化学反应模型,对流项采用5阶MPWENO格式求解,时间方向采用3阶TVD Runge-Kutta法,粘性项采用中心差分格式进行离散。结果表明:粘性和热传导不会对爆轰波流场的基本流场结构产生影响;在具体数值上,粘性和热传导的影响值在爆轰波、斜激波、接触间断等速度或温度剧烈变化处相对较大,但总体上其影响量均比爆轰波流场的步进值小三个量级。因此,在没有壁面效应的一维爆轰和二维连续旋转爆轰波流场中,粘性和热传导项作为很小的扰动存在,对爆轰波的流场结构和数值大小基本不会产生影响。     

弯管内爆轰波传播的流场显示和数值模拟

采用激光纹影系统拍摄了爆轰波在不同位置的流场照片. 用二阶附加半隐的龙格- 库塔法和五阶WENO格式 分别离散欧拉方程时间和空间导数项,用基元反应来描述爆轰化学反应过程,获得了压力、 温度、典型组元质量分数分布及数值胞格结构和爆轰波平均速度. 结果表明：受壁面稀疏波 和压缩波影响,爆轰波阵面发生畸变. 但由于弯管曲率半径较大,未出现爆轰波熄灭. 靠近 凹壁面的激波强度大于凸壁面侧,且凹壁面侧的反应区宽度较凸壁面侧要窄. 弯管出口处的 三波点数目较入口处减少,爆轰波衰减. 在出口直段,受扰动的爆轰波可恢复为自持爆轰波. 爆轰波流场、胞格结构、平均爆轰波速度的计算和实验结果定性一致.     

激波绕射碰撞加速诱导爆轰的数值模拟

基于单步化学反应的Euler方程和对激波(爆轰波)、接触间断具有良好捕捉效果的Roe/HLL混合格式以及自适应网格技术,模拟了激波在方形管中与方块障碍物相互作用,并发生绕射碰撞来诱导爆轰的过程.结果表明,弱激波在绕经方块时,形成上、下绕射激波并在方块尾部发生碰撞,生成局部高温高压点,可加快爆轰的形成;而当管内阻塞比超过...     

氢氧爆轰波在变截面扩张管道中传播的数值模拟

采用二阶精度频散控制耗散格式(DCD)和8组分20个方程的基元反应模型,对轴对称变截面管道中氢氧爆轰波传播进行数值模拟。结果表明,爆轰波传播至突变截面扩张管道时,由于稀疏波的作用可能会使爆轰波局部熄爆甚至完全熄爆,对于某些敏感度高的反应气体爆轰波可以二次起爆。而在渐变截面扩张管道爆轰波相对不易熄爆。     

基于主-次激波在变截面管中传播的数值模拟

采用二阶精度的单调迎风中心格式(MUSCL)和非结构自适应网格技术与有限体积形式,对轴对称变截面管道中基于主-次的爆轰波传播过程进行了数值模拟。结果表明,基于主-次的爆轰波传播至目标区时,冲击波流场均匀、稳定,波形良好;适当提高驱动段的爆炸能量,目标区能够获得预想的冲击波超压值和作用时间。     

三维气相爆轰动态并行计算程序设计与开发

在三维气相爆轰数值研究中,网格精度和计算域的规模导致网格数占有非常庞大的计算资源,进而给数值模拟带来了极大的挑战。本文针对这一难题,采用5阶WENO格式对带化学反应Euler方程组进行空间离散,基于MPI（MessagePassingInterface）并行模式开发了高精度动态并行代码,并对爆轰波在带有障碍物的三维方形管道中的传播过程进行计算。计算结果表明,高精度动态并行计算能够很好的模拟三维气相爆轰波在大尺寸管道中的传播,不仅提高了计算效率,而且提高了爆轰波阵面的分辨率。与高精度静态并行相比,高精度动态并行计算减少了界面数据通信时间,从而进一步提高了计算效率。因此,高精度动态并行程序为探究三维气相爆轰新的物理机制提供有效的手段。     

多流体界面不稳定性的守恒和非守恒高精度数值模拟方法

对多流体界面问题守恒和非守恒格式(M)WENO重构方法进行探讨,采用虚拟流动方法并用Level-Set函数捕捉界面的运动变化。数值模拟结果表明本文的数值方法具有较高的分辨率,并能有效地抑制界面附近的非物理振荡。     

Development of level set method with good area preservation to predict interface in two‐phase flows

A two‐step conservative level set method is proposed in this study to simulate the gas/water two‐phase flow. For the sake of accuracy, the spatial derivative terms in the equations of motion for an incompressible fluid flow are approximated by the coupled compact scheme. For accurately predicting the modified level set function, the dispersion‐relation‐preserving advection scheme is developed to preserve the theoretical dispersion relation for the first‐order derivative terms shown in the pure advection equation cast in conservative form. For the purpose of retaining its long‐time accurate Casimir functionals and Hamiltonian in the transport equation for the level set function, the time derivative term is discretized by the sixth‐order accurate symplectic Runge–Kutta scheme. To resolve contact discontinuity oscillations near interface, nonlinear compression flux term and artificial damping term are properly added to the second‐step equation of the modified level set method. For the verification of the proposed dispersion‐relation‐preserving scheme applied in non‐staggered grids for solving the incompressible flow equations, three benchmark problems have been chosen in this study. The conservative level set method with area‐preserving property proposed for capturing the interface in incompressible fluid flows is also verified by solving the dam‐break, Rayleigh–Taylor instability, bubble rising in water, and droplet falling in water problems. Good agreements with the referenced solutions are demonstrated in all the investigated problems. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐order upwind compact scheme and simulation of turbulent premixed V‐flame

A high‐order accurate upwind compact difference scheme with an optimal control coefficient is developed to track the flame front of a premixed V‐flame. In multi‐dimensional problems, dispersion effect appears in the form of anisotropy. By means of Fourier analysis of the operators, anisotropic effects of the upwind compact difference schemes are analysed. Based on a level set algorithm with the effect of exothermicity and baroclinicity, the flame front is tracked. The high‐order accurate upwind compact scheme is employed to approximate the level set equation. In order to suppress numerical oscillations, the group velocity control technique is used and the upwind compact difference scheme is combined with the random vortex method to simulate the turbulent premixed V‐flame. Distributions of velocities and flame brush thickness are obtained by this technique and found to be comparable with experimental measurement. Copyright © 2005 John Wiley & Sons, Ltd.     

A combined finite volumes - finite elements method for a low-Mach model

In this paper, we develop a finite volumes - finite elements method based on a time splitting to simulate some low-Mach flows. The mass conservation equation is solved by a vertex-based finite volume scheme using a τ-limiter. The momentum equation associated with the compressibility constraint is solved by a finite element projection scheme. The originality of the approach is twofold. First, the state equation linking the temperature, the density, and the thermodynamic pressure is imposed implicitly. Second, the proposed combined scheme preserves the constant states, in the same way as a similar one previously developed for the variable density Navier-Stokes system. Some numerical tests are performed to exhibit the efficiency of the scheme. On the one hand, academic tests illustrate the ability of the scheme in term of convergence rates in time and space. On the other hand, our results are compared to some of the literature by simulating a transient injection flow as well as a natural convection flow in a cavity.     

RKDG有限元方法计算流体与刚体耦合

用Level set方法配合Runge-Kutta discontinuous Galerkin (RKDG)有限元方法求解流体与刚体耦合问题。用RKDG有限元方法求解欧拉方程,通过求解Level set方程对界面进行追踪,并用推广的Ghost fluid方法对流刚界面进行处理。数值实验表明,该方法具有较高的分辨率。由于该方法不需要对移动网格进行处理,因此可以处理任意形状的拓扑问题,并且很容易推广到三维。     

Effect of initial disturbance on the detonation front structure of a narrow duct

The effect of an initial disturbance on the detonation front structure in a narrow duct is studied by three-dimensional numerical simulation. The numerical method used includes a high-resolution fifth-order weighted essentially non-oscillatory scheme for spatial discretization, coupled with a third-order total variation diminishing Runge-Kutta time-stepping method. Two types of disturbances are used for the initial perturbation. One is a random disturbance which is imposed on the whole area of the detonation front, and the other is a symmetrical disturbance imposed within a band along the diagonal direction on the front. The results show that the two types of disturbances lead to different processes. For the random disturbance, the detonation front evolves into a stable spinning detonation. For the symmetrical diagonal disturbance, the detonation front displays a diagonal pattern at an early stage, but this pattern is unstable. It breaks down after a short while and it finally evolves into a spinning detonation. The spinning detonation structure ultimately formed due to the two types of disturbances is the same. This means that spinning detonation is the most stable mode for the simulated narrow duct. Therefore, in a narrow duct, triggering a spinning detonation can be an effective way to produce a stable detonation as well as to speed up the deflagration to detonation transition process.     

破碎带波浪的数值模拟

基于一组色散关系得到改进的完全非线性Boussinesq方程建立了一个波浪模型可以模拟近岸水域的波浪变浅、破碎以及在海滩上的爬高等多种变形。波浪破碎引起的能量衰减是在动量方程中引入一个在空间和时间上都只作用于波前的涡粘项来模拟。动海岸线边界用窄缝法处理。波浪爬高用非线性浅水方程推导的非破碎波浪在斜坡上爬高的解析解来验证。本模型还模拟了波浪在斜坡上不同类型的破碎变形过程,并将其波高和平均水位的沿程变化和物理模型实验的结果比较,两者符合良好。     

不稳定性对爆轰波楔面马赫反射的影响规律研究

采用一种两步化学反应模型对胞格爆轰波的楔面马赫反射过程进行了数值研究,从而澄清和解释胞格不稳定性对马赫反射发展模式和自相似性的影响。考虑到反应欧拉方程源项的刚性问题,本文采用附加RungeKutta方法耦合非刚性对流项和刚性反应源项,对流项的离散采用五阶精度的WENO格式。计算结果表明,对于稳定胞格爆轰波而言,其马赫反射过程本质上与ZND爆轰波的马赫反射是一致的,整体上不存在自相似性,胞格不稳定性只是造成了三波点轨迹线局部小振幅的波动。在楔面顶点附近,由于马赫杆是强过驱的,爆轰波的马赫反射过程是自相似的。在远场,爆轰波马赫反射的三波点轨迹线渐近的趋向于一条直线,说明重新获得了自相似性。对于不稳定的爆轰波,由于自身的不稳定性可以与马赫反射的强度相匹配,定义其三波点的轨迹是困难的,进行自相似性分析没有意义。