Development of an integral LES model for turbulent premixed combustion at elevated pressures

一次能源仍然通常由燃烧过程提供。在许多技术应用中，如燃气轮机燃烧室或增压活塞发动机，燃烧是在高压下进行的。由于化石燃料的高能量密度，在可预见的未来，它们是商用飞机的不可替代的，至少在中期，尽管电气化程度不断提高，活塞发动机仍将用于传统或混合动力驱动。为了优化流动和燃烧过程，缩短开发周期，节约成本，数值模拟变得越来越重要。具体地说，大涡模拟(LES)方法近年来已成为流动模拟的重要工具，并已用于第一次工业构型。许多物理过程可以用大涡模拟来解决，而不是像过去经常做的那样，对所有的湍流尺度进行建模。然而，在现有的大涡模拟亚网格燃烧模型中，很少考虑压力的影响，对于高压燃烧，模型往往没有得到足够的验证。流体动力不稳定性的发生可能会导致更强烈的火焰起皱，这也经常被忽略。最后，需要封闭的不同模式项之间以及与数值格式之间的强烈相互作用变得越来越明显。这些单独的部件不应被视为彼此独立，更换时应小心。该项目的总体目标是开发和验证高压湍流预混燃烧的整体大涡模拟。该项目分为两个紧密相连的部分。首先，建立了不同压力下湍流平面火焰和本生火焰的域名系统数据库。随后，对数据进行空间过滤以产生伪LES场(先验分析)。通过这种方式，可以将建模方法与非封闭项进行比较，并且可以识别出有前途的模型。然而，对一个模型的评估最终只能在真实的LES中进行，也就是所谓的后验分析。这是项目第二部分的范围。所选择的闭合方法在大涡模拟流动解算器中实现，并使用文献中的DNS数据和实验数据进行了验证。LES还将展示不同子模型之间的相互作用。在第二个应用阶段，分析和模型开发将扩展到空燃比在空间上变化的情况。这将通过使用详细的化学机制建立分层湍流火焰的域名系统数据库来实现。

Primary energy is still often supplied by combustion processes. In many technical applications, such as gas turbine combustion chambers or supercharged piston engines, combustion takes place at elevated pressure. Due to the high energy density of fossil fuels, they are without alternative for commercial aircrafts in the foreseeable future and at least medium-term, despite increasing electrification, piston engines will still be used in conventional or hybrid drives. In order to optimize the flow and combustion process as well as to reduce development times and to save costs, numerical flow simulation is becoming increasingly important. Specifically, the large eddy simulation (LES) approach has become an important tool for flow simulation in recent years and is already used for first industrial configurations. Instead of modelling all turbulent scales, as often done in the past, many physical processes can be resolved with LES. However, in existing LES subgrid combustion models the effect of pressure has rarely been taken into account, the models are often insufficiently validated regarding high-pressure combustion. The occurrence of hydrodynamic instabilities, which can lead to a stronger flame wrinkling, is also often ignored. Finally, it is becoming more and more apparent that different model terms to be closed interact strongly with one another as well as with the numerical scheme. These individual parts should not be considered independent of each other and care should be taken when they are replaced. The overall goal of this project is the development and validation of an integral LES model for high pressure turbulent premixed combustion. The project is divided into two closely interlinked parts. First, a DNS data base is created for turbulent planar and Bunsen flames at different pressures. Subsequently, the data is spatially filtered to produce pseudo-LES fields (a-priori analysis). In this way modeling approaches can be compared with unclosed terms and promising models can be identified. However, the assessment of a model can ultimately only take place in a real LES, the so-called a posteriori analysis. This is the scope of the second part of the project. The previously selected closure approaches are implemented in an LES flow solver and validated using DNS data and experimental data from literature. The LES will also show the interaction of different submodels. In a second application period, the analyses and the model development will be extended to situations with spatially varying air-fuel ratio. This will be done by building a DNS data base of stratified turbulent flames using detailed chemical mechanisms.