Scale-resolving Simulations of Multicomponent Nozzle Flows

该项目详细研究了直接喷射系统中氢气在空气中的喷射和混合过程。由于高的入口压力，建立了一个欠膨胀的超音速流，其中发生了复杂的相互作用的激波系统和湍流。这会影响混合位置和物种分布;同样，预计热力学参数会产生显著影响。 来流或喷管几何形状的不均匀性导致了复杂的非线性行为。这不仅影响燃烧，而且可能是间歇性循环变化的因果链的一部分。这个分项目的目标是将这些混合过程的特性描述为已确定参数的函数。为此，高分辨率的大涡模拟欠膨胀氢喷射进行。空间和时间中的能量承载尺度的分辨率对于捕获多尺度多物理场效应以及间歇现象是绝对必要的。在这里，湍流区和激波系统的共存对数值计算提出了巨大的挑战。 此外，发生的尺度的差异（例如，在喷嘴喉部和直径之间超过3个数量级）不能用具有全局恒定网格间距的计算网格来表示，即使在高性能计算机上也是如此。因此，国家的最先进的高阶方法与适应能力，可以适应当地的网格分辨率发生的尺度在这里使用。这些方法在本项目中扩展为多组分流。通过这些方法，喷嘴流动以及随后的混合可以以前所未有的精度得到解决，并与实验结果进行比较。基于这种方法，热力学参数（状态方程，扩散方法）的影响，进一步研究与合作伙伴项目的数值和实验。由此产生的高分辨率流场以及被动平流示踪粒子的粒子轨迹将被耦合到燃烧模拟代码，考虑到并行化的要求。一方面，这将关闭从喷嘴到燃烧的模拟链，另一方面，它将允许对发生的变化进行联合调查（通过相关分析以及示踪剂）。多层次和多保真度的方法被用来验证结果对喷嘴流量的变化。总的来说，该项目应有助于可靠和高度准确的氢气注入和混合映射，从而有助于预测周期波动，并更好地了解其原因。

The project investigates in detail the injection and mixing processes of hydrogen in air, as they occur in direct injection systems. Due to the high inlet pressure, an underexpanded supersonic flow is established, in which a complex interaction of shock systems and turbulence occurs. This influences the mixing location and species distribution; likewise, a significant effect of thermodynamic parameters is to be expected. Uncertainties in inflow or nozzle geometry contribute to the complex, nonlinear behavior. This not only affects combustion but may also be part of the causal chain of intermittent cyclic variations. The characterization of these mixing processes as a function of the identified parameters is the goal of this subproject. For this purpose, high-resolution large eddy simulations of underexpanded hydrogen injections are performed. The resolution of the energy-carrying scales in space and time is absolutely necessary to capture the multiscale-multiphysics effects as well as the intermittent phenomena. Here, the coexistence of turbulent regions and shock systems pose great challenges to numerics. Additionally, the disparity of the occurring scales (e.g., more than 3 orders of magnitude lie between nozzle throat and diameter) cannot be represented with computational grids with globally constant grid spacing, even on high-performance computers. Therefore, state-of-the-art high-order methods with adaptation capabilities are used here, which can adapt the local grid resolution to the occurring scales. These methods are extended in this project for multi-component flows. With these methods, the nozzle flow as well as the subsequent mixing can be resolved with unprecedented accuracy and compared to the experimental results. Based on this methodology, the influence of the thermodynamic parameters (equation of state, diffusion approach) is further investigated in cooperation with numerical and experimental partner projects. The resulting high-resolution flow fields as well as the particle trajectories of passively advected tracer particles will be coupled to the combustion simulation code, taking into account the parallelization requirements. On the one hand, this will close the simulation chain from the nozzle to the combustion, and on the other hand, it will allow a joint investigation of the occurring variations (by correlation analysis as well as tracers). Multi-level and multi-fidelity methods are used to validate the results against changes in the nozzle flow. Overall, this project should contribute to a reliable and highly accurate mapping of hydrogen injection and mixing and thus to a contribution to the prediction of cyclic fluctuations and to a better understanding of their causes.