钝体驻定湍流扩散火焰的数值研究——燃烧模型比较

分别采用标量联合的概率密度函数方法、稳态火焰面模型、Euler非稳态火焰面模型和基于有限体积/Monte Carlo混合算法的完备PDF模型对钝体驻定的Sydney湍流扩散火焰HM1进行数值模拟,以比较不同燃烧模型的性能,并比较标量联合的概率密度函数方法和Euler非稳态火焰面模型对氮氧化物排放预测的差异.计算结果和实验数据的比较表明,采用概率密度函数方法计算化学反应可以得到更好的结果但计算量较大,而用火焰面模型求解计算量较小,在接近完全燃烧的情形下,其计算结果比较合理.     

Hydromagnetic slip flow with heat transfer in an inclined channel

The problem of steady two-dimensional laminar flow in slip flow regime of a viscous incompressible and electrically conducting fluid through an inclined channel of rectangular cross-section in presence of a transverse magnetic field has been considered. The walls of the channel are assumed to have prescribed temperatures and finite conductivities. The expressions for the velocity component, induced magnetic field and the temperature are obtained and their numerical results are shown graphically.     

弯曲矩形管道内充分发展流动的数值研究——第一部分:层流

该文给出了正交曲线坐标下Navier-Stokes方程的积分形式,介绍了动力学方程积分法和Poisson方程的快速求解法,对弯曲矩形管道内充分发展层流流动进行了数值研究,其结果与其它计算实验结果进行了比较.     

用随机方法解河渠非恒定流

随机水力学是水力学研究的一个新发展。本文应用确定性模型与随机模型相结合的方法,对明渠非恒定渐变流的计算进行了研究。采用Saint Venant方程组为系统模型,但对系统的输入如明渠的糙率、过水断面、水力半径等,则采用适当的随机模型,产生的输出(流量、水位随时间和位置的变化)是随机性的、本文以柘溪水电站下游河道作为实例,用计算机进行了计算,并与实测结果作了印证。     

Numerical study of the flow around a cylinder using multi-particle collision dynamics

A novel mesoscopic simulation technique--multi-particle collision dynamics--which has been suggested very recently, is used to study the two-dimensional flow around a square and a circular cylinder. The method is described and new proper boundary conditions are proposed to deal with wall collisions. The flow is analyzed in a wide range of Reynolds numbers in order to cover both the steady and unsteady regimes, resulting in symmetric steady vortices and periodic vortex shedding, respectively. The numerical results for integral flow parameters, such as the recirculation length, the drag and lift coefficients, the Strouhal number, as well as the spatial dependence of the velocity field, are compared with previous numerical and experimental studies. The qualitative and quantitative agreement is very good, validating the method as a promising technique to describe the hydrodynamic effects of solvent on embedded particles.     

低温液体输送过程中的参数计算与分析

首先分析了在稳定的单相流中液体温升和压力损失的计算方法 ,然后介绍了在稳定的两相流中如何计算流体的流量及出口液体的蒸气含量 ,最后对三种最常见的非稳定过程 :管路被冷却、填充盲支管以及打开阀门进行了分析 ,并分析了在这三种情况下如何确定压力波动的最大值     

N-S方程隐式分区并行计算

将Wu Z N和Zou H提出的一套适合三点块三对角隐式格式的定常和非定常可压无粘流的覆盖分区并行计算方法推广到N-S方程的计算.在二维定常亚音速、跨音速和非定常情况下都得到了较好的绝对并行效率.     

最小二乘有限元法求解非定常应力的Navier-Stokes方程

为精确求解非定常层流问题,发展一种非定常速度-应力-压力的方法.采用牛顿法对非线性对流项进行线性化处理和预处理共轭梯度法,实现了非定常应力形式Navier-Stokes方程的求解.方腔层流流动比较发现,非定常应力形式比涡量形式与试验结果更加吻合,精度更高.该方法有效地解决亚格子应力项的问题,实现基于最小二乘有限元法的湍流求解.比较方腔湍流流动的试验与仿真结果,证明本文的方法具有可行性,为湍流大涡模拟计算打下基础.     

矩形通道内层流对流换热的最优速度场

针对矩形通道内的层流对流换热问题,通过数值求解速度场协同方程,得到了给定黏性耗散条件下通道内的最优速度场为多纵向涡的流动结构,表明多纵向涡流型可在流阻增加不多的情况下使换热显著强化.通过在通道壁面布置不连续双斜肋,在通道内产生了接近于最优速度场的多纵向涡流动,数值计算结果表明,在Re=1000时,与光滑通道相比,不连续...     

跨音压气机转子近失速工况叶尖非定常流动分析

对跨音压气机Rotor35进行单通道全三维定常/非定常数值模拟,并与试验总性能和流场分布对比校核了数值计算精度。以此为基础开展的近失速工况点的非定常计算发现,来自相邻叶片通道未形成泄漏涡的间隙泄漏流体与来流、激波与泄漏涡干涉形成的低能破碎区相互作用形成了叶尖二次涡。叶尖二次涡向下游运动过程中,其所处的位置和产生的阻塞影响了近叶顶载荷的分布,最终使得叶尖部流场出现了循环往复的自维持的非定常波动现象。     

Framework for simulating stationary spherical flames

Understanding and quantifying the effects of flame stretch rate on the laminar flame speed and flame structure plays an important role from interpreting experimentally-measured laminar burning velocities to characterizing the impact of turbulence on premixed flames. Unfortunately, accounting for these effects often requires an unsteady reacting flow solver and may be computationally expensive. In this work, we propose a mathematical framework to perform simulations of stationary spherical flames. The objective is to maintain the flame at a constant radius (and hence a constant stretch rate) by performing a coordinate change. The governing equations in the new flame-attached frame of reference resemble the original equations for freely-propagating spherical flames. The only difference is the presence of additional source terms whose purpose is to drive the numerical solution to a steady state. These source terms involve one free parameter: the flame stretch rate, which may either be computed in real time or imposed by the user. This parameter controls ultimately the steady state flame radius and the steady state flame speed. That is why, at a given stretch rate, the results of the stationary spherical flame simulations match those of a freely-expanding spherical flame. As an illustration, the dependence of the laminar flame speed on the stretch rate is leveraged to extract Markstein lengths for hydrogen/air mixtures at different equivalence ratios, as well as for hydrocarbon/air mixtures (CH₄ and C₇H₁₆). Numerical predictions are in good agreement with experimental measurements (within experimental uncertainties). Finally, the proposed methodology is implemented in the chemical kinetic software FlameMaster. The use of a dedicated steady-state solver with a non-uniform optimized mesh leads to significant reductions in the computational cost, highlighting that the proposed methodology is ideally suited for other chemical kinetic software such as Chemkin/Premix and Cantera.     

A quantitative method for a priori evaluation of combustion reaction models

In recent years, direct numerical simulations have been used increasingly to evaluate the validity and performance of combustion reaction models. This study presents a new, quantitative method to determine the ideal model performance attainable by a given parameterization of the state variables. Data from direct numerical simulation (DNS) of unsteady CO/H₂–air jet flames is analysed to determine how well various parameterizations represent the data, and how well specific models based on those parameterizations perform. Results show that the equilibrium model performs poorly relative to an ideal model parameterized by the mixture fraction. The steady laminar flamelet model performs quite well relative to an ideal model parameterized by mixture fraction and dissipation rate in some cases. However, at low dissipation rates or at dissipation rates exceeding the steady extinction limit, the steady flamelet model performs poorly. Interestingly, even in many cases where the steady flamelet model fails (particularly at low dissipation rate), the DNS data suggests that the state may be parameterized well by the mixture fraction and dissipation rate. A progress variable based on the CO₂ mass fraction is proposed, together with a new model based on the CO₂ progress variable. This model performs nearly ideally, and demonstrates the ability to capture extinction with remarkable accuracy for the CO/H₂ flames considered.     

叶型优化在非定常流动条件下效果的数值分析

本文对叶型优化在非定常流动条件下的效果进行数值研究。叶型优化基于比较成熟的在定常流动条件下的反问题解法，非定常流动则考虑到动静叶栅之间的相互作用，非定常流动的求解在Ｎ－Ｓ方程的基础上采用分区计算的方法来完成。数值计算的结果表明，定常流动条件下优化得到的叶型在非定常流动条件下同样具有较好的气动性能。     

PISO算法在求解方柱绕流非定常尾迹中的应用

应用PISO算法及非交错斜交网格技术,编制了求解二维定常、非定常流动的通用程序。计算分析了定常不可压缩Couette流动以及水平通道内方柱绕流尾迹的非定常流动,并详细分析了不同时刻方柱后尾迹的旋涡结构及发展过程,得到了合理的结果。验证了非迭代PISO算法及非交错斜交网格在分析非定常流动中的有效性,为进一步开展非定常流动的数值分析奠定了基础．     

叶栅内定常及非定常粘性流动数值模拟

本文给出了一个模拟叶栅内准三维定常和非定常粘性流动的数值方法。对于定常流动,采用ＴＶＤ Ｌａｘ－Ｗｅｎｄｒｏｆｆ格式和代数湍流模型求解雷诺平均Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程,使用当地时间步长和多网格技术使计算加速收敛到定常状态;对于非定常流动,使用双时间步长和全隐式离散,采用与求解定常流动相似的多网格方法求解隐式离散方程。文中给出了ＶＫＩ透平叶栅内的定常流结果和１．５级透平叶栅内的非定常数值结果。     

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采用FLUENT软件分别对外加均匀横向磁场的等截面三维充分发展液态金属管流的层流模型和低雷诺数湍流Lam/Bremhost(LB)模型进行了数值模拟,分析了外加磁场对普通方管LB模型速度分布和压降的影响。比较在相同哈特曼数下,层流和湍流模型方管截面上速度分布和管道中MHD压降。其中,对电流的计算采用磁感应方程来求得。数值模拟结果证明了用低雷诺数LB湍流模型解决方管磁流体流动的可行性。通过层流模型和湍流模型的对比可知,层流模型有较短的入口长度,但管内流体的压降却很大;而湍流模型管内速度更加平均化,管内压降较小,但管内入口长度较长。     

强声波作用下烟气中滑移单颗粒煤粉传热传质特性

根据二维轴对称、非稳态,层流的质量、动量和能量守恒方程,研究强声波作用下烟气中滑移单颗粒煤粉的传热传质特性,颗粒与烟气之间有稳定的滑移速度.分析声压级范围为150 dB~170 dB,可听声频率范围内,及在声质点速度与滑移速度的不同速率比情况下,颗粒局部努赛尔数、表面平均努赛尔数以及时间-空间平均努赛尔数的分布规律.在可听声频率范围内,存在极值频率,此时煤颗粒表面的传热传质效果最佳.为强声波应用于电站锅炉中、强化煤颗粒燃烧提供理论基础.     

基于特征线理论的辨识法在激波装配中的应用

准确地给出激波位置信息对于激波装配极为重要.但是,在使用计算流体力学（computational fluid dyna-mics,CFD）方法模拟复杂流动时很难准确地给出激波的位置.根据激波捕捉得到的流场信息确定的激波位置往往带有极大误差,在定常问题的模拟中,这种误差可以随着迭代逐渐消除,然而在非定常问题的模拟中,这种误差往往会积累甚至导致计算崩溃.文章将基于特征线理论的激波辨识技术应用到激波装配中,根据已有流场信息准确判断激波的位置.对于定常问题,该方法的应用加速了收敛速度;对于非定常问题,该方法的应用可以极大地避免初始误差的产生.      

底部加热长方体腔内自然对流的非线性特性

采用SIMPLE算法,QUICK差分格式,对底部加热三维长方体腔内空气的自然对流进行了数值模拟。根据模拟结果,探讨了方腔内流体流动与换热的静态分岔与振荡等非线性现象。数值结果显示,在固定的几何尺寸和不同Ra的情况下,当初始场不同时,会出现若干不同的解,即存在解的静态分岔;在固定的几何尺寸和相同的初始场情况下,低Ra时流动和换热处于稳态,当Ra超过某一临界值时,流动和换热就会随时间振荡,并通过倍周期分岔过渡到混沌;当方腔的几何尺寸不同时,分岔点的特征值Ra也发生变化。     

Computational study of the laminar to turbulent transition over the SD7003 airfoil in ground effect

In this work, we present a numerical study of the laminar-turbulence transition flow around a symmetrical air-foil at a low Reynolds number in free flow and near the ground surface at different angles of attack. Finite volume method is employed to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. In this way, the Transition SST turbulence model is used for modeling the flow turbulence. Flow around the symmetrical airfoil SD7003 is numerically simulated in free stream and near the ground surface. Our numerical method can detect different aspects of flow such as adverse pressure gradient, laminar separation bubble and laminar to turbulent transition onset and the numerical results are in good agreement with the experimental data.