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稀薄预混燃烧而设计的。然而，为了保证点火和操作安全，需要进行一些局部燃料分层，从而导致燃料-空气混合物的不均匀性。更高的吞吐量和减小燃烧室尺寸的额外要求可能会增加湍流水平，使得主要火焰状态从小火焰状态转变为薄火焰状态。当前的燃烧模型通常基于小火焰假设，并且当前没有模型能够可靠地预测燃料分层和小火焰状态的偏差。本研究将开发一种基于粒子的蒙特卡罗方法，用于模拟湍流预混火焰。每个蒙特卡罗 (PDF) 粒子都代表流体元素的瞬时局部解。然后，这些瞬时解可以近似气相化学成分的联合概率密度函数（PDF），从而近似预混合火焰的内部结构。借助大涡模拟 (LES)，在欧拉框架中求解速度场守恒方程。分子和湍流扩散的建模提出了主要挑战：将标准混合模型应用于预混燃烧会导致整个火焰前锋的不受控制和非物理混合，从而阻碍了火焰结构甚至燃烧速度的准确预测。该工作的新颖之处在于使用稀疏粒子方法来计算气相成分 PDF。传统的粒子方法每个 LES 单元需要 20 到 50 个粒子，并且其数值求解成本可能极其昂贵。使用稀疏方法时，粒子数量可以降低到每 10 个 LES 单元 1 个以下，并且可以显着减少模拟时间。这是通过在参考场上调节混合算子来实现的。正是这个参考场可用于将扩散建模为多步过程，防止整个火焰前锋的混合，确保预热区颗粒温度的持续升高，并限制颗粒点火和热量释放到反应区。首先，简单的统计一维火焰的直接数值模拟（DNS）将有助于新封闭件的开发。然后，DNS 配置将扩展到包括燃料分层。最后一步，新的封闭装置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。