Sparse-Lagrangian Particle Methods for Spray Combustion

喷雾燃烧的稀疏拉格朗日粒子方法

• 批准号: 390544712
• 负责人: Professor Dr. Andreas Kronenburg
• 金额: --
• 依托单位: Institut für Technische Verbrennung (ITV)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/390544712?language=en
• 关键词: Sparse; Lagrangian; Particle; Methods; Spray

Stochastic particle methods shall be developed for the modelling of turbulent spray combustion. Stochastic particle methods are suited for the modelling of two-phase flows if one phase can be understood as a continuum and the other phase can be represented by discrete droplets. These conditions hold in most combustion chambers after primary spray breakup, and a Lagrangian method can be used for the modelling of the droplets’ conservation equations. In addition, we use a particle-based Monte Carlo method for the approximation of the joint probability density function (PDF) of the chemical composition of the gas phase. Every Monte Carlo (PDF) particle represents an instantaneous, local solution of a fluid element, the closure problems of classical moment methods can be avoided, and the chemical source term is given in closed form. Particle methods are therefore ideally suited for the modelling of reactive two-phase flows. The conservation equations for the velocity field are solved in an Eulerian framework with the aid of large-eddy simulations (LES). The novelty of the proposed work is the use of a sparse particle method for the computation of the gas phase composition PDF. Conventional particle methods require between 20 and 50 particles per LES cell and their numerical solution can be extremely costly. The particle number can be lowered to less than 1 particle per 10 LES cells when using sparse methods, and simulation times can be reduced by up to 2 orders of magnitude for cases with complex chemistry. The modelling of mass and heat transfer across the phase interface, i.e. the transfer between the disperse liquid droplets and the PDF (gas phase) particles is, however, a significant challenge and requires novel modelling approaches. Closures cannot easily be adapted from conventional (dense) particle methods. A variety of alternative closures has been investigated in the first funding period using direct numerical simulations (DNS) of a droplet laden double shear layer configuration. Only DNS allows for an explicit (and isolated) analysis of particle pairing (i.e. selection of the gas phase particle to receive the mass from the droplet) and the speed of the mixing between (i.e. the mixing time scale) between the two phases, and this isolation of certain physical processes facilitates the development of new closures. MMC-LES of laboratory spray flames continue, however, to feature distinct deviations from experimental data since real spray flames are unlikely to burn entirely within the non-premixed combustion regimes and droplets may not be dispersed everywhere. In the second funding period, the models shall therefore be extended to cover a variety of process and flame conditions such as partially premixed flames and dense spray flames, and they will then be validated with the aid of available experimental data.

应发展随机粒子方法来模拟湍流喷雾燃烧。随机粒子方法适用于两相流动的模拟，如果一相可理解为连续介质，另一相可用离散液滴表示。这些条件在初级喷雾破裂后的大多数燃烧室中都适用，并且可以用拉格朗日方法来模拟液滴的守恒方程。此外，我们使用基于粒子的蒙特卡罗方法来逼近气相化学组成的联合概率密度函数(PDF)。每个蒙特卡罗(PDF)粒子代表一个流体元素的瞬时局部解，避免了经典矩方法的闭合问题，并且化学源项以闭合形式给出。因此，质点方法非常适合于反应性两相流的模拟。速度场的守恒方程在欧拉框架下借助大涡模拟(LES)求解。这项工作的创新之处在于使用了一种稀疏粒子方法来计算气相组成PDF。传统的粒子方法需要每个LES单元20到50个粒子，而且它们的数值解可能非常昂贵。当使用稀疏方法时，粒子数可以减少到每10个LES单元中不到1个粒子，对于复杂化学情况，模拟时间可以减少多达2个数量级。然而，相界面上的传质和传热的模拟，即分散的液滴和PDF(气相)颗粒之间的传递是一个巨大的挑战，需要新的模拟方法。闭包不能很容易地从传统的(密集的)粒子方法中进行修改。在第一个供资期间，使用液滴加载的双剪切层构型的直接数值模拟(DNS)对各种替代关闭进行了研究。只有DNS允许对颗粒配对(即选择从液滴接收质量的气相颗粒)和两相之间的混合速度(即混合时间尺度)进行显式(和隔离)分析，并且这种对某些物理过程的隔离有助于开发新的闭塞。然而，实验室喷雾火焰的MMC-LE仍然具有与实验数据明显的偏差，因为真正的喷雾火焰不太可能完全在非预混燃烧区域内燃烧，并且液滴可能不会分散到所有地方。因此，在第二个资助期，模型应扩大到涵盖各种工艺和火焰条件，如部分预混火焰和密集喷雾火焰，然后将借助现有的实验数据进行验证。