DNS characterisation and LES modelling of the primary and secondary breakup of structure-viscous liquid jets

如果液体射流从圆形喷嘴喷出，射流就会分解。射流破碎描述了液体体积分解成复杂的液滴系统的过程。在靠近喷嘴的区域中发生的主要射流破碎代表了一个重要且难以建模的子过程，其次是二次破碎。在这个过程中，已经形成的液滴的动力学起着重要的作用。流体雾化是一个基本的技术过程，其应用范围广泛，如燃烧系统中的燃料喷射，杀虫剂的应用，医疗喷雾，反应堆冷却，组件喷涂，喷雾干燥，消防等等。非牛顿流体用于许多应用中（例如，在绘画或医疗喷雾剂中）。虽然这些流体的性质在较简单的情况下是时间无关的，例如剪切稀化流体，但在更复杂的情况下，例如粘弹性流体，存在对时间的额外依赖性。在这一建议的背景下，基本的，详细的数值研究的射流破碎的液体射流与非牛顿行为进行。这项工作致力于剪切稀化和触变液体。数值研究分为直接数值模拟（DNS）和大涡模拟（LES）。对于多相流的描述，使用流体体积（VOF）方法。借助DNS计算，详细研究了液体射流的基本破碎机理。相关的影响，如粘度对射流形态和破碎过程进行了识别，描述和量化。由此，LES所需的模型被导出并集成到LES代码中。在大涡模拟中，单个亚网格液滴被视为拉格朗日点。大涡模拟不仅可以研究液体射流的初次破碎，还可以研究液体射流的二次破碎。因此，开发了一种方法来模拟具有非牛顿性质和蒸发的射流破碎过程，例如在喷雾干燥过程中发生。蒸发条件下改变过程中射流breaking.This建议是由两个申请人（慕尼黑/斯图加特）谁补充对方非常好的数值方法（DNS/LES）方面实施的详细调查。因此，它是可能的调查的主要以及二次射流破碎的非牛顿液体射流的详细情况下，它使用多尺度LES方法建模，并进一步了解这些复杂的过程。

If a liquid jet is ejected from a round nozzle, the jet disintegrates. Jet breakup describes the process of disintegration of the liquid volume into a complex system of droplets. The primary jet breakup, occurring in the area close to the nozzle, represents an important and difficult to model sub-process and is followed by the secondary breakup. In this process, the dynamics of already formed droplets play an important role. Fluid atomisation is a fundamental technical process with applications as diverse as fuel injection in combustion systems, application of insecticides, medical sprays, reactor cooling, painting of components, spray drying, firefighting and much more. Non-Newtonian fluids are used in many applications (e.g. in painting or medical sprays). While the properties of these fluids are time-independent in simpler cases, e.g. shear-thinning fluids, in more complex cases, such as viscoelastic fluids, there is an additional dependence on time. In the context of this proposal, fundamental, detailed numerical investigations of the jet break-up of liquid jets with a non-Newtonian behavior are carried out. This work is dedicated to both shear-thinning and thixotropic liquids. The numerical investigations are divided into Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). For the description of the multiphase flow the Volume of Fluid (VOF) method is used. With the help of DNS calculations, basic break-up mechanisms in the liquid jet are investigated in detail. The relevant influences e.g. viscosity on the jet morphology and the breakup process are identified, described and quantified. From this, models required for the LES are derived and integrated into the LES code. In the LES, single sub-grid droplets are treated as Lagrange points. With the help of the LES, the primary breakup, but also the secondary breakup of the liquid jet, can be investigated. Thus, a methodology is developed to simulate the jet breakup processes with non-Newtonian properties and evaporation, as it occurs e.g. during spray drying. The conditions under which evaporation changes the processes during jet breakup are also investigated in detail.This proposal is implemented by two applicants (Munich/Stuttgart) who complement each other very well with regard to the numerical methods used (DNS/LES). Thus, it is possible to investigate the primary as well as the secondary jet breakup of non-Newtonian liquid jets in detail, to model it using a multiscale LES approach and to further understand these complex processes.