旋流杯燃烧室流场的数值与试验研究

本文在任意曲线坐标系下对旋流杯环形燃烧室冷态和两相燃烧全流程流场进行数值研究。采用RNG k-ε湍流模型,EBU-Arrhenius燃烧模型和六通量辐射模型模拟湍流燃烧过程;采用颗粒轨道模型模拟两相流动。为了验证数学模型与计算方法,本文还采用PIV测量燃烧室火焰筒内冷、热态流场,利用温度耙测量燃烧室出口温度径向分布,所得的计算值与试验数据符合较好,表明所用的各数学模型合理、计算方法可行,所得研究结果可为该类燃烧室的优化设计提供有用的依据。     

等离子体对含硼两相流扩散燃烧特性的影响

为排除来流空气对含硼燃气的掺混效应, 研究等离子体对含硼富燃料推进剂在补燃室二次燃烧过程的影响, 建立了含硼两相流平行进气扩散燃烧物理模型. 利用高速摄影仪拍摄了含硼燃气在补燃室二次燃烧的火焰图像, 分析了该物理模型的扩散燃烧特性和硼颗粒的二次点火距离. 采用硼颗粒的King点火模型、有限速度/涡耗散模型、颗粒轨道模型和RNG k-ε模型以及等离子体模型, 模拟了一定条件下等离子体对含硼两相流扩散燃烧过程的影响. 结果表明, 依据含硼燃气二次燃烧图像得到的硼颗粒二次点火距离, 与数值模拟结果基本一致, 保证了该物理模型和计算方法的可靠性. 含硼两相流经过等离子体区域后, 硼颗粒在运动轨迹上颗粒温度明显增加, 颗粒直径明显减小, B₂O₃的质量分数分布区域明显扩增, 70%的硼颗粒在到达补燃室2/3尺寸前燃烧效率已达到100%, 硼颗粒充分燃烧释放出更多热量导致中心流线区域温度增加近1/2, 可见等离子体可以明显强化含硼两相流的燃烧过程, 提高硼颗粒的燃烧效率.     

颗粒Reynolds正应力轨道模型及后台阶两相流动数值模拟

用随机过程理论建立气固两相耦合脉动量Lagrange方程,并建立了气固两相流随机颗粒轨道模型中颗粒Reynolds正应力的Lagrange方程.将新的模型运用于各向同性的湍流衰减的流场中,模拟颗粒的湍流扩散特性,与文[1]中的模型和实验结果作比较,并使用新模型模拟了后台阶两相流动.     

煤粉挥发分火焰行为的理论分析与简化模拟方法

考虑热解的扩展连续膜模型,可以详细预报煤粉挥发分析出、焦碳燃烧的全过程.模型以CH4燃烧的反应动力学特性,近似地描述了挥发分火焰.提出新的简化模拟方法均相着火后挥发分燃烧的移动火焰锋面(MFFVC)模型,弥补了挥发分现有计算方法中未考虑颗粒边界层内挥发分均相着火及燃烧的不足.与挥发分现有计算方法、扩散控制的挥发分燃烧(DLVC)模型相比, MFFVC模型预报与考虑热解的扩展连续膜模型符合较好.     

炉内两相流动和煤粉燃烧的双流体-轨道模型

本文首次用双流体一轨道（连续介质－轨道ＣＴ）模型对大尺寸四角喷燃炉内气粒两相流动及煤粉燃烧进行了模拟。该模型基于欧拉气相方程组、欧拉颗粒连续方程和动量方程以及拉氏颗粒能量和质量变化的方程,对各子模型用ｋ－ε－ｋｐ两相湍流模型,ＥＢＵ－Ａｒｒｈｅｎｉｕｓ湍流燃烧模型,煤粉颗粒的水分蒸发,热解挥发和焦炭燃烧的扩散－动力模型,ＤＯ（离散坐标）辐射模型。采用了将坐标扭转一定角度的方法减小入口射流和网格斜交造成的伪扩散。编制了ＬＥＡＧＡＰ－ＦＵＲＮＡＣＥ－３程序,分别对冷态模型炉内两相流动和大尺寸炉内三维两相流动和煤粉燃烧进行了模拟,并与颗粒轨道（ＳＴ）模型的模拟结果进行了对照。采用ＰＤＰＡ对冷态模型炉内气粒两相流场进行了测量。冷态两相流动的模拟与实验结果的对比表明ＣＴ模型的模拟结果和实验符合较好,ＳＴ模型所得颗粒浓度分布和实验山入较大。热态模拟的结果给出了两相速度,气相温度,组分浓度和壁面热流分布。模拟结果定性合理。模拟结果显示在出口处由于气流旋转,有一局部高温区存在。     

三维煤粉燃烧全双流体模型的数值模拟

1引言目前煤粉燃烧综合模型最为广泛的是以轨道模型为基础，美国杨伯翰大学的先进燃烧工程中心（CERC）自1980年起研制二维煤粉燃烧程序PCGC－2，从1990年起研制三维煤粉燃烧的PCGC－3程序[1]。与轨道模型发展的同时，美国Rabcock＆Wilcox公司Fiveland[2]等人研制了FURMO程序，用无滑移模型对560MW侧墙喷燃煤粉炉进行了三维全模拟。其特点是首次用全欧拉的处理方法计算三维煤粉燃烧过程，其不足之处是不考虑气粒两相间的速度滑移和温度滑移．总的看来，用轨道模型模拟煤粉燃烧，易于考虑颗粒反应经历，也可给出两相之间的速度及温…     

不同前驱体模型对航空煤油扩散火焰碳烟颗粒生成的影响研究

采用不同的航空煤油化学反应机理和碳烟成核模型对气态航空煤油扩散火焰中碳烟颗粒的质量浓度和数量浓度进行预测.分别采用航空煤油详细化学反应机理和简化化学反应机理,结合非预混稳态扩散火焰面模型模拟燃烧反应.分别采用C2H2成核模型(基于乙炔浓度)和PAH成核模型(基于多环芳香烃浓度)预测碳烟颗粒浓度分布.研究结果表明,采用详细化学反应机理和PAH成核模型对碳烟体积分数的预测值与试验值吻合很好.相比于C2H2成核模型,采用PAH成核模型对碳烟体积分数的预测精度显著提升.     

煤粉射流火焰的DNS研究

本文用直接数值模拟(DNS)的方法对煤粉气固两相射流燃烧进行了研究。文章介绍了DNS的数值计算方法,包括气相、颗粒相的控制方程以及煤粉燃烧模型。分析了煤粉射流燃烧火焰的结构形态,发现火焰区域中存在三种火焰形态,通过火焰特性的统计研究,发现虽然火焰形态不同,但是其燃烧特性相似,非预混火焰占主导地位。分析火焰释热量,发现上游处单颗粒燃烧释热量较小,条带状释热量占24%,对下游稳定火焰的形成至关重要。     

镁颗粒群着火和燃烧过程数值模拟

建立了一维非稳态球形镁颗粒群的着火燃烧模型, 数值模拟镁颗粒群的着火和燃烧过程, 研究表明, 颗粒群着火首先发生在颗粒群边界, 随后初始的燃烧火焰会分离为两个, 一个向颗粒群内部传播, 一个向外部传播, 最终内部火焰消失, 外部火焰维持并控制着整个颗粒群的燃烧; 内火焰向颗粒群内部传播过程中, 传播速度会逐渐加快, 且火焰温度值呈逐渐降低趋势. 分析了颗粒群内部参数和环境参数对镁颗粒群着火燃烧的影响. 随颗粒浓度的增大, 颗粒群着火时间略有增长, 但火焰传播速度更快, 燃烧稳定时火焰球尺寸也更大. 颗粒群初温越高, 则颗粒群着火时间越短, 火焰传播速度也会加快, 但燃烧稳定时火焰球尺寸基本不变. 环境温度对颗粒群着火燃烧的影响较复杂, 环境温度越高, 颗粒群着火时间越短, 但火焰传播速度却越慢, 燃烧稳定时火焰球尺寸变化很小. 颗粒粒径和辐射源温度对颗粒群着火燃烧的影响较显著, 颗粒粒径越小或辐射源温度越高, 则颗粒群着火时间越短, 火焰传播速度越快, 燃烧稳定时火焰球尺寸也越大. 数值模拟结果与文献中试验结果相一致. 关键词： 粉末燃料冲压发动机 镁着火燃烧 颗粒群     

铝颗粒粉尘对冲火焰数值模拟研究

铝颗粒由于具有能量密度高、易储存、燃烧过程不产生温室气体等优势,有望成为未来化石燃料替代的解决方案.本文建立了铝颗粒粉尘火焰的燃烧模型,其中考虑了相间传热、相变、表面化学反应、气相详细化学反应及辐射传热等过程,并针对铝颗粒粉尘对冲火焰开展了数值模拟研究.首先,通过仿真McGill大学的铝颗粒粉尘对冲火焰实验进行模型验证,并分析了实验中使用铝颗粒本身作为示踪粒子引起的气相速度测量误差,结果表明,数值模拟得到的离散相速度分布与实验结果基本一致,火焰传播速度的预测值也同实验数据吻合较好.当颗粒粒径小于10μm时,连续介质假设不再成立,相间传热模型必须考虑过度区机制,随着颗粒粒径的增加,火焰传播速度不断降低.随着对冲火焰拉伸率的增加,颗粒在火焰区的停留时间减少,并出现燃烧不完全的现象,粉尘火焰由双峰变为单峰结构.火焰传播速度随着拉伸率的增加而增大,通过线性外推可得到未拉伸的火焰传播速率约为29 cm/s.辐射引起的热损失会导致气相温度大幅降低,但辐射传热对颗粒的加热作用相对较小.     

Investigation of the structure of a polydisperse gas-droplet jet in the initial region. Experiment and numerical simulation

The structure of gas-droplet polydisperse jet was studied experimentally and numerically. Experiments were carried out using the Particle Image Velocimetry/Particle Tracking Velocimetry/Interferometric Particle Imaging methods, which allowed simultaneous measurements of parameters for the average and pulsation carrying and disperse phases. Gas phase turbulence was calculated using the model of Reynolds stresses transfer. Significantly non-isotropic character of velocity pulsation of particles along and across the section of the gas-droplet jet was demonstrated in experiments and calculations. Strong dependence of axial pulsations of disperse phase velocity on the size of its particles is observed.     

Enhanced linearized reduced-order models for subsurface flow simulation

Trajectory piecewise linearization (TPWL) represents a promising approach for constructing reduced-order models. Using TPWL, new solutions are represented in terms of expansions around previously simulated (and saved) solutions. High degrees of efficiency are achieved when the representation is projected into a low-dimensional space using a basis constructed by proper orthogonal decomposition of snapshots generated in a training run. In recent work, a TPWL procedure applicable for two-phase subsurface flow problems was presented. The method was shown to perform well for many cases, such as those with no density differences between phases, though accuracy and robustness were found to degrade in other cases. In this work, these limitations are shown to be related to model accuracy at key locations and model stability. Enhancements addressing both of these issues are introduced. A new TPWL procedure, referred to as local resolution TPWL, enables key grid blocks (such as those containing injection or production wells) to be represented at full resolution; i.e., these blocks are not projected into the low-dimensional space. This leads to high accuracy at selected locations, and will be shown to improve the accuracy of important simulation quantities such as injection and production rates. Next, two techniques for enhancing the stability of the TPWL model are presented. The first approach involves a basis optimization procedure in which the number of columns in the basis matrix is determined to minimize the spectral radius of an appropriately defined amplification matrix. The second procedure incorporates a basis matrix constructed using snapshots from a simulation with equal phase densities. Both approaches are compatible with the local resolution procedure. Results for a series of test cases demonstrate the accuracy and stability provided by the new treatments. Finally, the TPWL model is used as a surrogate in a direct search optimization algorithm, and comparison with results using the full-order model demonstrates the efficacy of the enhanced TPWL procedures for this application.     

Neutron Star Matter Including Delta Isobars

In this paper a new phase structure of neutron star matter including nucleons and delta isobars is presented.Particle fractions populated and pion condensations in neutron star matter are investigated in this model. The existence of the pion condensations can postpone the appearance of delta isobars. We found that both the pion condensation and reduce of the ratio of delta isobar to nucleons couplings can soften the corresponding equation of state. The maximum masses and their corresponding radii of neutron stars are calculated, and the obtained values are in observational region.     

Neutron Star Matter Including Delta Isobars

In this paper a new phase structure of neutron star matter including nucleons and delta isobars is presented. Particle fractions populated and pion condensations in neutron star matter are investigated in this model. The existence of the pion condensations can postpone the appearance of delta isobars. We found that both the pion condensation and reduce of the ratio of delta isobar to nucleons couplings can soften the corresponding equation of state. The maximum masses and their corresponding radii of neutron stars are calculated, and the obtained values are in observational region.     

Spectral Structure and Doublon Dissociation in the Two-Particle Non-Hermitian Hubbard Model

Strongly-correlated systems in non-Hermitian models are an emergent area of research. Herein, a non-Hermitian Hubbard model is considered, where the single-particle hopping amplitudes on the lattice are not reciprocal, and provide exact analytical results of the spectral structure in the two-particle sector of Hilbert space under different boundary conditions. The analysis unveils some interesting spectral and dynamical effects of purely non-Hermitian nature and that deviate from the usual scenario found in the single-particle regime. Specifically, a spectral phase transition of the Mott-Hubbard band on the infinite lattice is predicted as the interaction energy is increased above a critical value, from an open to a closed loop in complex energy plane, and the dynamical dissociation of doublons, i.e., instability of two-particle bound states, in the bulk of the lattice, with a sudden revival of the doublon state when the two particles reach the lattice edge. Particle dissociation observed in the bulk of the lattice is a clear manifestation of non-Hermitian dynamics arising from the different lifetimes of single-particle and two-particle states, whereas the sudden revival of the doublon state at the boundaries is a striking burst edge dynamical effect peculiar to non-Hermitian systems with boundary-dependent energy spectra, here predicted for the first time for correlated particles.     

J~P assignments of Λ_c~+ baryons

The "good" diquark is employed to study Λ_c~+ baryons within a mass loaded flux tube model. The study indicates that all Λ_c~+ baryons candidates in the 2008 review by the Particle Data Group (PDG) are well described in the mass loaded flux model. The quantum numbers J~P of these Λ_c~+ candidates are assigned. If Λ_c(2765)~+ is an orbitally excited Λ_c~+, it is likely the J~P=3~+/2 one. If Λ_c(2765)~+ is an orbitally excited Σ_c, there ought to be another J~P = 3~+/2 Λ_c~+ with mass ≈ 2770 MeV. In the model, there exists no J~P = 1~+/2 Λ_c~+ (≈ 2700) predicted in existing literature. Λ_c(2940)~+ is very possible the orbitally excited baryon with J~P = 5~-/2.     

喷动流化床的数值模拟研究

本文借鉴 Ｃｕｎｄａｌｌ＆ Ｓｔｒａｃｋ提出的碰撞模型,将欧拉方法和拉格朗日法结合起来,建立了喷动流化床气固两相流动的数学模型,在计算机上对试验台进行了模拟,探讨了床内颗粒的运动特征。按１：１的比例建立了喷动流化床的模型试验台并进行了试验,对模拟结果和试验结果进行了比较与分析。颗粒在喷动床内的运动特征,模拟结果都能够再现出来,模拟结果与试验结果取得了很好的一致性。     

Effect of Cu doping on the static dielectric constant of nanocrystalline ZnO

Cu-doped ZnO nanoparticles were synthesized by a simple rheological phase reaction–precursors method using zinc acetate, cupric acetate and oxalic acid for different atomic percentages of Cu doping. X-ray diffraction studies confirmed the correct phase formation and compositions were obtained by energy dispersive X-ray analysis. Particle sizes were recorded from small angle X-ray scattering studies. The static dielectric constant, calculated from the shift in band-gap energy, showed a gradual decrease with Cu doping. A simple theoretical calculation, based on the Penn model, was performed to explain the observed change in dielectric constant with doping. The model could successfully describe the dependence of the static dielectric constant of nanocrystalline ZnO on doping concentration.     

Application of the conditional source-term estimation model for turbulence–chemistry interactions in a premixed flame

Conditional Source-term Estimation (CSE) is a closure model for turbulence–chemistry interactions. This model uses the first-order CMC hypothesis to close the chemical reaction source terms. The conditional scalar field is estimated by solving an integral equation using inverse methods. It was originally developed and has been used extensively in non-premixed combustion. This work is the first application of this combustion model for a premixed flame. CSE is coupled with a Trajectory Generated Low-Dimensional Manifold (TGLDM) model for chemistry. The CSE-TGLDM combustion model is used in a RANS code to simulate a turbulent premixed Bunsen burner. Along with this combustion model, a similar model which relies on the flamelet assumption is also used for comparison. The results of these two approaches in the prediction of the velocity field, temperature and species mass fractions are compared together. Although the flamelet model is less computationally expensive, the CSE combustion model is more general and does not have the limiting assumption underlying the flamelet model.