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.

新颖的燃烧器概念主要是为精益预混合燃烧而设计的。为了确保点火和操作安全，需要一些当地的燃料分层，但是导致燃油空气混合物的不均匀性。较高吞吐量和减小燃烧室的尺寸的其他要求可能会增加湍流水平，从而使主要火焰状态从火焰中转移到薄片机制。当前的燃烧模型通常基于火焰的假设，并且没有当前模型可以可靠地预测燃料分层和与火焰状态的偏差。拟议的研究将开发一种基于粒子的蒙特卡洛方法，用于建模湍流预混合火焰。每个蒙特卡洛（PDF）粒子代表流体元件的瞬时局部溶液。然后，这些瞬时溶液允许对气相的化学组成的关节概率密度函数（PDF）以及预混合火焰的内部结构的近似值。速度场的保护方程式在欧拉框架中借助大型模拟（LES）来解决。分子和湍流扩散的建模构成了主要的挑战：将标准混合模型应用于预混合燃烧到未经整体和无形的燃烧导致整个燃烧的结构，从而使范围的结构变得越来越高。提出的工作的新颖性是使用稀疏粒子方法来计算气相组成PDF。常规的粒子方法需要每个LES细胞的20至50个颗粒，其数值解决方案可能非常昂贵。当使用稀疏方法时，粒子的数量可以降低至每10个LES细胞的少于1个粒子，并且可以大大减少模拟时间。这是通过参考字段上混合操作员的条件来实现的。正是该参考字段可用于模拟扩散作为多步过程，可防止在火焰前面混合，并确保在预热区域中粒子温度的持续升高，并将颗粒点火和热释放限制为反应区域。首先直接的数值模拟（DNS）简单，统计上的一维火焰将有助于开发新的封闭的开发。然后，将扩展DNS配置以包括燃料分层。在最后一步中，新的关闭将应用于真实的实验室火焰，并将借助可用的实验数据进行验证。