环形燃烧室火焰简及旋流器流场计算

本文采用偏微分方程法生成贴体网格,在任意曲线坐标系下数值研究两种先进燃烧室火焰筒及其旋流器三维紊流流场。由于旋流器的形状复杂,本文采用型线定点法确定网格的边界。在非交错网格系下采用SIMPLE算法和混合差分格式对离散方程进行求解。计算结果表明计算方法合理,这计算程序进一步扩展,可用来预估环形燃烧室反应流流场。     

短突扩压器流场计算

本文在三维贴体坐标系下对短环突扩扩压器进行流声计算．利用偏微分方程法和曲面论生成三维贴体网格，在按非交错网格系统求解各守恒方程时，采用抑制措施，避免压力振荡产生．考虑到扩压器是多通道区域，本文采用区域法进行数值分析，计算结果表明本计算方法合理可行．     

水斗曲面三维非正交贴体网格数值生成

为实现冲击式水轮机水斗内非定常流动的数值解析,需要高密度匀布非正交贴体坐标网格来拟合水斗曲面.本文开发了一种用于水斗曲面三维非正交贴体坐标匀布网格的数值生成程序,其主要算法是基于曲线与曲面的微分几何性质提出的四点投影法.程序可根据需要计算出不同密度的匀布贴体网格点.通过对两不同水斗的算例结果显示数值生成的网格很好地拟合了水斗不规则曲面,同时计算出各网格点的切向矢量和单位法向矢量.     

贴体坐标网格生成技术的研究

本文对数值求解微分方程法生成贴体坐标网格的技术进行了探讨和尝试。文中不仅对数值求解双调和方程的两种不同方法作了介绍,还利用该方程生成了典型的Ｈ型、Ｃ型、Ｏ型网格。结果表明,双调和方程法在控制网格线间距及与边界的正交性方面具有很强的能力,所生成的网格质量令人满意,且可用于复杂的物理区域。因而,采用双调和方程生成贴体坐标网格是流场数值模拟中一种有效的、高质量、具有广泛通用性的网格生成技术。     

贴体坐标系下模型加力室的大涡模拟

本文利用贴体网格对带V形槽稳定器模型加力燃烧室素流化学反应流流动进行大涡模拟的研究。采用区域法生成模型加力燃烧室的二维贴体网格,并采用多区域耦合法进行区域之间的数据传递,求解加力室整体流场。采用k方程亚网格尺度模型和亚网格EBU燃烧模型分别估算其亚网格紊流粘性和化学反应速率,用热通量辐射模型估算辐射通量,并用交错网格下SIMPLE算法和混合差分格式求解离散方程,壁面函数处理固壁边界条件。计算结果显示了稳定器后面的回流区气流结构,所得的热态流场模拟结果与实验比较吻合,表明采用贴体网格对模型加力燃烧室进行大涡模拟能真实反映流体流动及燃烧过程。     

用于叶轮机械复杂流动的网格自适应方法

高质量的网格生成是叶轮机械复杂流动准确预测的关键技术之一。目前在大部分结构网格生成过程中,网格拓扑及局部网格密度均基于经验或粗略的估计,此类网格一般需要根据计算结果进行手动调整。本文发展了基于多块贴体结构化网格的网格自适应技术以达到自动调整局部网格密度并在不严重增加计算量的前提下改进计算精度的目的。本文基于真实物理流动机理,提出了有效的网格加密判据,可以自动判断激波和涡等复杂流动。在此基础上本文发展了可以保证网格质量的贴体网格加密技术。通过一系列算例验证了本文发展的网格自适应技术的有效性和实用性.结果表明:本文方法可以自动捕捉流动细节并根据当地流动尺度自动调整局部网格尺度;同时相对于全局网格加密,本文方法可以达到改进精度和节省计算量之间的平衡。     

环形燃烧室内气相燃烧及两相流动计算

采用TTM法与型线定点法相结合的方式生成带涡流器环形燃烧室贴体网格,在任意曲线坐标系中对其三维两相反应流场进行数值模拟,采用的紊流、燃烧以及辐射模型分别为:标准k-ε方程,EBU-Arrhenius公式,六通量热辐射模型等。在同位网格系下气相采用SIMPLE算法求解,气液两相流动用PSIC法模拟。通过对两种燃烧室的计算结果与实验值比较表明本计算方法合理,所得的计算结果可为环形燃烧室的优化设计提供指导数据。     

复杂全机外形跨音速绕流欧拉方程数值计算

发展了一种快速抛物型方程贴体及与边界正交网格生成技术。生成了某歼击机全机真实外形三维O-C型计算网格,并应用于跨音速流场欧拉方程数值计算。成功地模拟了绕全机的复杂流场。计算压力分布与实验吻合良好。     

结合前沿推进的Delaunay三角化网格生成及应用

采用一种新的混合网格生成方法,生成复杂区域的非结构化网格.结合前沿推进法和Delaunay三角化两种非结构网格生成方法的特点,在边界处采用前沿推进法进行三角形初始网格的生成,在边界区域内部采用Delaunay三角化方法自动生成内部节点.分析表明,该算法简化网格生成过程,能够快速有效地生成非结构化网格.在计算时间以及网格的均匀性方面与其他方法相比具有一定的优势.最后,用混合网格生成方法生成方柱绕流的计算域网格,并运用基于特征线方程的分离算法进行流场计算.     

二维网格生成技术及其应用

本文采用解析变换生成二维贴体、正交网格。对变换的精度及对流场解的影响以及如何对网格生成进行控制、形成与流场参数变化相适应的网格分布等问题以NACA0012翼型为例进行了深入地探讨,并成功地应用于欧拉方程数值解。     

Identification and analysis of instability in non-premixed swirling flames using LES

Large eddy simulations (LES) of turbulent non-premixed swirling flames based on the Sydney swirl burner experiments under different flame characteristics are used to uncover the underlying instability modes responsible for the centre jet precession and large scale recirculation zone. The selected flame series known as SMH flames have a fuel mixture of methane-hydrogen (50:50 by volume). The LES solves the governing equations on a structured Cartesian grid using a finite volume method, with turbulence and combustion modelling based on the localised dynamic Smagorinsky model and the steady laminar flamelet model respectively. The LES results are validated against experimental measurements and overall the LES yields good qualitative and quantitative agreement with the experimental observations. Analysis showed that the LES predicted two types of instability modes near fuel jet region and bluff body stabilised recirculation zone region. The mode I instability defined as cyclic precession of a centre jet is identified using the time periodicity of the centre jet in flames SMH1 and SMH2 and the mode II instability defined as cyclic expansion and collapse of the recirculation zone is identified using the time periodicity of the recirculation zone in flame SMH3. Finally frequency spectra obtained from the LES are found to be in good agreement with the experimentally observed precession frequencies.     

A multi-block ADI finite-volume method for incompressible Navier–Stokes equations in complex geometries

An efficient second-order accurate finite-volume method is developed for a solution of the incompressible Navier–Stokes equations on complex multi-block structured curvilinear grids. Unlike in the finite-volume or finite-difference-based alternating-direction-implicit (ADI) methods, where factorization of the coordinate transformed governing equations is performed along generalized coordinate directions, in the proposed method, the discretized Cartesian form Navier–Stokes equations are factored along curvilinear grid lines. The new ADI finite-volume method is also extended for simulations on multi-block structured curvilinear grids with which complex geometries can be efficiently resolved. The numerical method is first developed for an unsteady convection–diffusion equation, then is extended for the incompressible Navier–Stokes equations. The order of accuracy and stability characteristics of the present method are analyzed in simulations of an unsteady convection–diffusion problem, decaying vortices, flow in a lid-driven cavity, flow over a circular cylinder, and turbulent flow through a planar channel. Numerical solutions predicted by the proposed ADI finite-volume method are found to be in good agreement with experimental and other numerical data, while the solutions are obtained at much lower computational cost than those required by other iterative methods without factorization. For a simulation on a grid with O(10⁵) cells, the computational time required by the present ADI-based method for a solution of momentum equations is found to be less than 20% of that required by a method employing a biconjugate-gradient-stabilized scheme.     

Impact of co- and counter-swirl on flow recirculation and liftoff of non-premixed oxy-flames above coaxial injectors

Controlling the flame shape and its liftoff height is one of the main issues for oxy-flames to limit heat transfer to the solid components of the injector. An extensive experimental study is carried out to analyze the effects of co- and counter-swirl on the flow and flame patterns of non-premixed oxy-flames stabilized above a coaxial injector when both the inner fuel and the annular oxidizer streams are swirled. A swirl level greater than 0.6 in the annular oxidizer stream is shown to yield compact oxy-flames with a strong central recirculation zone that are attached to the rim of central fuel tube in absence of inner swirl. It is shown that counter-swirl in the fuel tube weakens this recirculation zone leading to more elongated flames, while co-swirl enhances it with more compact flames. These results obtained for high annular swirl levels contrast with previous observations made on gas turbine injectors operated at lower annular swirl levels in which central recirculation of the flow is mainly achieved with counter-rotating swirlers. Imparting a high inner swirl to the central fuel stream leads to lifted flames due to the partial blockage of the flow at the injector outlet by the central recirculation zone that causes high strain rates in the wake of the injector rim. This partial flow blockage is more influenced by the level of the inner swirl than its rotation direction. A global swirl number is then introduced to analyze the structure of the flow far from the burner outlet where swirl dissipation takes place when the jets mix. A model is derived for the global swirl number which well reproduces the evolution of the mass flow rate of recirculating gases measured in non-reacting conditions and the flame liftoff height when the inner and outer swirl levels and the momentum flux ratio between the two streams are varied.     

An Elliptic Grid Generation Technique for the Flow Contraction

In this paper, we determined a numerical solution of the incompressible Navier-Stokes equations for the flow inside the contraction geometry. The governing equations are written in the vorticity-stream function formulations. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system by transforming the governing equation into computational plane. The transformed equations are approximated using central differences and solved simultaneously by successive over-relaxation iteration.     

A high-resolution mapped grid algorithm for compressible multiphase flow problems

We describe a simple mapped-grid approach for the efficient numerical simulation of compressible multiphase flow in general multi-dimensional geometries. The algorithm uses a curvilinear coordinate formulation of the equations that is derived for the Euler equations with the stiffened gas equation of state to ensure the correct fluid mixing when approximating the equations numerically with material interfaces. A γ-based and a α-based model have been described that is an easy extension of the Cartesian coordinates counterpart devised previously by the author [30]. A standard high-resolution mapped grid method in wave-propagation form is employed to solve the proposed multiphase models, giving the natural generalization of the previous one from single-phase to multiphase flow problems. We validate our algorithm by performing numerical tests in two and three dimensions that show second order accurate results for smooth flow problems and also free of spurious oscillations in the pressure for problems with interfaces. This includes also some tests where our quadrilateral-grid results in two dimensions are in direct comparisons with those obtained using a wave-propagation based Cartesian grid embedded boundary method.     

Numerical simulation for the flow inside V-shapes using grid generation

In this paper, we determined a numerical solution of the Navier-Stokes equations for the flow of incompressible fluid inside the contraction geometry. The governing equations are written in the vorticity-stream function formulations. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system by transforming the governing equation into the computational plane. The transformed equations are approximated using central differences and solved simultaneously by the alternating direction implicit method and successive over relaxation iteration method.     

Effect of swirl on combustion dynamics in a lean-premixed swirl-stabilized combustor

The effect of inlet swirl on the flow development and combustion dynamics in a lean-premixed swirl-stabilized combustor has been numerically investigated using a large-eddy-simulation (LES) technique along with a level-set flamelet library approach. Results indicate that when the inlet swirl number exceeds a critical value, a vortex-breakdown-induced central toroidal recirculation zone is established in the downstream region. As the swirl number increases further, the recirculation zone moves upstream and merges with the wake recirculation zone behind the centerbody. Excessive swirl may cause the central recirculating flow to penetrate into the inlet annulus and lead to the occurrence of flame flashback. A higher swirl number tends to increase the turbulence intensity, and consequently the flame speed. As a result, the flame surface area is reduced. The net heat release, however, remains almost unchanged because of the enhanced flame speed. Transverse acoustic oscillations often prevail under the effects of strong swirling flows, whereas longitudinal modes dominate the wave motions in cases with weak swirl. The ensuing effect on the flow/flame interactions in the chamber is substantial.     

一种基于特征理论模拟凝聚炸药爆轰的单元中心型Lagrange方法

提出一种数值模拟凝聚炸药爆轰问题的单元中心型Lagrange方法.利用有限体积离散爆轰反应流动方程组,基于双曲型偏微分方程组的特征理论获得离散网格节点的速度与压力,获得的网格节点速度与压力用于更新网格节点位置以及计算网格单元边的数值通量.以这种方式获得的网格节点解是一种"真正多维"的理论解,是一维Godunov格式在二维Riemann问题的推广.有限体积离散得到的爆轰反应流动的半离散系统使用一种显-隐Runge-Kutta格式来离散求解：显式格式处理对流项,隐式格式处理化学反应刚性源项.算例表明,提出的单元中心型Lagrange方法能够较好地模拟凝聚炸药的爆轰反应流动.     

三维曲光轴坐标下的旁轴电子光学

从费马原理出发，应用微分几何的曲线坐标定义，给出了三维曲光轴坐标中电子在旁轴下的一级和二级近似轨迹方程式.借助于对电场和磁场的数值计算，可以分析电磁场分布和电子运动轨迹复杂情况下的电子光学性质.给出了对一种电子束扫描式扁平显像管电子光学系统的计算结果，并给以定性说明. 关键词：