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

一次能源仍然经常由燃烧过程提供。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，至少在中期，它们是商用飞机的替代品，尽管电气化程度越来越高，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，减少开发时间和节省成本，数值流动模拟变得越来越重要。具体来说，大涡模拟（LES）方法近年来已成为流动模拟的重要工具，并已用于首次工业配置。与过去经常模拟的所有湍流尺度不同，许多物理过程可以用LES来解决。然而，在现有的LES亚网格燃烧模型中，很少考虑压力的影响，对于高压燃烧模型的验证往往不够充分。流体动力不稳定性的发生会导致更强的火焰起皱，但也经常被忽视。最后，不同的模型项之间的相互作用以及与数值格式之间的相互作用越来越明显。这些单独的部件不应被认为是相互独立的，在更换它们时应小心。该项目的总体目标是开发和验证高压湍流预混燃烧的积分LES模型。该项目分为两个紧密相连的部分。首先，建立了湍流平面火焰和不同压力下本生火的DNS数据库。随后，对数据进行空间过滤以产生伪les字段（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，并可以识别有前途的模型。然而，对模型的评估最终只能在真实的LES中进行，即所谓的后验分析。这是项目第二部分的范围。前面选择的闭包方法在LES流求解器中实现，并使用DNS数据和文献中的实验数据进行验证。LES还将显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空间变化的情况。这将通过使用详细的化学机制建立分层湍流火焰的DNS数据库来完成。

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.