Curvature effects in laminar and turbulent non-premixed combustion

层流和湍流非预混燃烧中的曲率效应

• 批准号: 310695286
• 负责人: Professor Dr. Christian Hasse
• 金额: --
• 依托单位: Fachgebiet Simulation reaktiver Thermo-Fluid-Systeme
• 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/310695286?language=en
• 关键词: Curvature; effects; laminar; turbulent; non

In funding period 1 of the project, a comprehensive understanding of curvature effects in non-premixed combustion was achieved. In 10 peer-reviewed publications, it was shown that curvature-induced effects significantly influence the microstructure of laminar and turbulent diffusion flames. In addition to the simulation of canonical laminar flames, direct numerical simulations (DNS) of time-evolving turbulent jet flames (H2-air, syngas-air) were performed for this purpose, thus establishing a comprehensive reference database for the analysis of curvature effects. The analyses were summarized in a regime diagram for the assessment of curvature effects. A methodological highlight of funding period 1 is the in situ tracking of gradient trajectories (GTs) of the mixture fracture field in the DNS; individual GTs or flamelets can be tracked and analyzed in their spatial and temporal evolution. These Lagrangian data can be used to evaluate central model assumptions of the flamelet concept in turbulent flames. It has been shown that consideration of curvature in the flamelet equations alone is not sufficient for the prediction of curvature effects. Curvature-induced tangential diffusion along mixture fracture isosurfaces is the dominant effect in the case of large curvatures, which can only be fully described by the extended Flamelet equations. In the second funding period, the curvature influence on the auto-ignition of non-premixed turbulent flames will be investigated. In contrast to a (statistically) stationary diffusion flame, this is the preceding, highly transient process in which an unreacted (or slowly reacting) mixing layer quickly develops into a diffusion flame after an ignition delay time. Experiments and direct numerical simulations in the literature demonstrate that ignition kernels form along isosurfaces of a preferred mixture fraction, the "most reactive mixture fraction," in pockets of low scalar dissipation rate and negative curvature. Curvature effects can thus significantly influence ignition, but previous flamelet approaches have so far focused almost exclusively on the influence of scalar dissipation rate. The extension of flamelet theory to include curvature effects for steady-state conditions from funding period 1 is the starting point for modeling the transient auto-ignition of non-premixed flames. In addition to the analysis of the DNS data and the flamelet development, the transfer to the LES in funding period 2 is also targeted.

在项目的供资阶段1，全面了解了非预混燃烧中的曲率效应。在10篇同行评议的文献中，研究表明曲率诱导效应对层流和湍流扩散火焰的微观结构有显著影响。除了对正则层流火焰的模拟外，还为此目的进行了时间演化湍流喷流火焰(H2-空气、合成气-空气)的直接数值模拟，从而建立了一个全面的曲率效应分析参考数据库。这些分析总结在用于评估曲率效应的制度图中。供资阶段1的一个方法学亮点是原位跟踪数字地震系统中混合物裂隙场的梯度轨迹；可以跟踪和分析单个梯度轨迹或小片的空间和时间演变。这些拉格朗日数据可以用来评估湍流火焰中小火焰概念的中心模型假设。结果表明，仅在火焰面方程中考虑曲率是不足以预测曲率效应的。在大曲率的情况下，曲率诱导的沿混合型断裂等值面的切向扩散是主要的效应，这只能用扩展的Flamlet方程来描述。在第二个资助期，将研究曲率对非预混湍流火焰自燃的影响。与(统计上)静态扩散火焰不同，这是一个先前的、高度瞬变的过程，在此过程中，未反应(或缓慢反应)的混合层在点火延迟时间后迅速发展为扩散火焰。实验和文献中的直接数值模拟表明，在低标量耗散率和负曲率的凹坑中，点火核沿着首选混合物分数的等表面形成，该混合物分数是“最活跃的混合物分数”。曲率效应可以显著地影响点火，但到目前为止，以前的火焰面方法几乎完全集中在标量耗散率的影响上。从注资期1开始，火焰面理论扩展到包括稳态条件下的曲率效应，这是模拟非预混火焰瞬时自燃的起点。除了对域名系统数据的分析和火焰弹的开发外，在资金阶段2向LES的转移也是目标。