Unified modelling framework of sub- and super- critical injection dynamics

尽管许多以前的努力(主要是实验)来描述超临界注入条件，但由于控制它的复杂物理现象的多尺度、多相特征，它们仍然是一个具有挑战性的流体动力学问题。该建议旨在提供一种系统的方法，以便更好地理解和预测次临界到超临界喷射现象的转变，将新的最先进的模拟与布莱顿大学和桑迪亚国家实验室已经在柴油发动机条件下进行的实验相结合。该模型将包括真实的气体效应，并将一次雾化区域和二次雾化区域都定位在亚临界到超临界条件之间的过渡极限。目前，商业和开源的模拟工具还缺乏这样的方法。新的框架将在大涡模拟(LES)中开发，并将基于也用于火焰界面概率建模(表面密度方法)的思想的扩展。该方法的主要优点是，它不包括对计算单元中的液气体积分数的任何先验区域相关假设，并且绕过了组成喷雾的液体结构的球面视觉。因此，它可以同时适用于喷嘴附近和稀雾区，并且既代表了尖锐(如在亚临界喷射的情况下)，也代表了扩散(更能代表超临界条件)的界面。我们建议的数值模型即使在极端的热力学条件下也有可能捕捉到现象的基本物理，因此可以扮演“虚拟实验”的角色，提供有价值的进入流动区域和真实实验面临限制的条件的途径。将在拟议研究中提出的数字框架致力于创造新一代设备设计工具，这些工具将可供学术和非学术部门使用，并将促进新型高压注射系统的成本效益设计。此外，研究成果将通过在影响较大的期刊和国家和国际会议上发表的出版物以及外联讲习班向学术界传播。这些可能会改变我们目前看待多相问题建模的方式，不仅适用于汽车应用，也适用于涉及超临界流体的其他学科。

Despite many previous (mostly experimental) efforts to characterise super-critical injection conditions, they still remain a challenging fluid dynamics problem due to the multi-scale, multi-phase character of the complex physical phenomena that governs it. This proposal aims to offer a systematic approach towards a better understanding and prediction of the transition of sub- critical to super- critical injection phenomena, combining novel state of the art simulations with experiments already performed by the University of Brighton and Sandia National Laboratories for diesel engine conditions. The model will include real gas effects and target both primary and secondary atomization regions at the limit of transition between sub- critical to super- critical conditions. Such an approach is currently lacking from commercial and open source simulation tools. The new framework will be developed within Large Eddy Simulations (LES) and will be based on the extension of ideas also used in probabilistic modelling of flame interfaces (surface density approaches). The major strength of the approach is that it does not include any a priori region-dependent assumptions for the liquid-gas volume fraction in the computational cells, and bypasses the spherical vision of the liquid structures that compose the spray. Thus, it can be applicable both to the near-nozzle and the dilute spray areas, and represent both sharp (as in the case of sub- critical injection) and diffused (more representative of super-critical conditions) interfaces. Our suggested numerical models have the potential to capture the underlying physics of the phenomena even at extreme thermodynamic conditions and therefore can play the role of "virtual experiments", providing valuable access to flow areas and conditions where real experiments face limitations. The numerical framework that will be presented in the proposed research aspires to lead to the creation of the new generation of equipment design tools that will be available to both academic and non-academic sectors and will facilitate the cost effective design of novel high pressure injection systems. Moreover, the outcomes of the research will be disseminated to the academic community through publications in high impact journals and national and international conferences as well as an outreach workshop. These could change the way we currently view the modelling of multiphase problems not only for automotive application but for other disciplines involving super-critical fluids.