Sparse particle methods for turbulent premixed combustion

湍流预混燃烧的稀疏粒子方法

• 批准号: 393542303
• 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
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/393542303?language=en
• 关键词: Sparse; particle; methods; turbulent; premixed

Novel burner concepts are primarily designed for lean premixed combustion. To guarantee ignition and operational safety, some local fuel stratification is needed, however, leading to inhomogeneities of the fuel-air mixture. The additional requirements of higher throughput and a size reduction of the combustion chambers may increase the turbulence levels such that the predominant flame regime shifts from the flamelet to the thin-flame regime. Current combustion models are usually based on the flamelet assumption, and no current model can reliably predict fuel stratification and deviations from the flamelet regime.The proposed study will develop a particle based Monte Carlo method for the modelling of turbulent premixed flames. Every Monte Carlo (PDF) particle represents an instantaneous, local solution of a fluid element. These instantaneous solutions then allow for the approximation of the joint probability density function (PDF) of the chemical composition of the gas phase and thus of the inner structure of the premixed flame. The conservation equations for the velocity field are solved in a Eulerian framework with the aid of large-eddy simulations (LES).The modelling of molecular and turbulent diffusion pose the major challenge: the application of standard mixing models to premixed combustion leads to uncontrolled and unphysical mixing across the flame front that hinder the accurate prediction of the flame structure and even of the burning velocity. 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 significantly reduced. This is realized by conditioning of the mixing operator on a reference field. And it is this reference field that can be used to model diffusion as a multistep process that prevents mixing across the flame front and ensures a continuous increase of particle temperature in the preheat zone and limits particle ignition and heat release to the reaction zone.First, direct numerical simulations (DNS) of simple, statistically one-dimensional flames will aid the development of new closures. Then, the DNS configuration will be extended to include fuel stratification. In a final step, the new closures will be applied to real laboratory flames and will be validated with the aid of available experimental data.

新的燃烧器概念主要是为稀薄预混燃烧设计的。然而，为了保证点火和运行安全，需要一些局部燃料分层，从而导致燃料-空气混合物的不均匀。增加吞吐能力和减小燃烧室尺寸的额外要求可能会增加湍流程度，从而使主要火焰区域从小火焰区域转变为稀薄火焰区域。现有的燃烧模型通常基于火焰面假设，没有一个现有的燃烧模型能可靠地预测燃料分层和偏离火焰面的情况，本文将发展一种基于粒子的蒙特卡罗方法来模拟湍流预混火焰。每个蒙特卡罗(PDF)粒子代表一个流体元素的瞬时局部解。然后，这些瞬时解允许对气相化学成分的联合概率密度函数(PDF)进行近似，从而对预混火焰的内部结构进行近似。速度场的守恒方程在欧拉框架下借助大涡模拟(LES)求解。分子和湍流扩散的模拟是主要的挑战：将标准混合模型应用于预混燃烧会导致火焰锋面上的无控制和非物理混合，这阻碍了对火焰结构甚至燃烧速度的准确预测。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单元不到1个粒子，并且可以显著减少模拟时间。这是通过将混合算符限制在参考场上来实现的。正是这个参考场可以用来将扩散建模为一个多步骤过程，它防止了火焰前沿的混合，确保了预热区颗粒温度的持续增加，并将颗粒点火和热释放限制在反应区。首先，对简单的、统计上的一维火焰进行直接数值模拟(DNS)将有助于开发新的封口。然后，将扩展域名系统配置以包括燃料分层。在最后一步，新的封闭器将应用于真实的实验室火焰，并将借助现有的实验数据进行验证。