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Direct numerical simulation of aerodynamic fragmentation of liquid drops

液滴气动破碎的直接数值模拟

基本信息

批准号：
277161739
负责人：
Professor Dr.-Ing. Nikolaus Andreas Adams
金额：
--
依托单位：
Lehrstuhl für Aerodynamik und Strömungsmechanik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/277161739?language=en
关键词：
Direct numerical simulation aerodynamic fragmentation

项目摘要

The destruction of gas-liquid interfaces of a liquid phase dispersed as droplets in gas by fast inertial effects is called aerodynamic fragmentation or aero-breakup. Technical applications of such processes are widely spread, involve e.g. secondary fragmentation of sprays of fuels, melts, paints, coatings, or biomedical emulsions. Process optimization requires understanding of physical mechanisms and, eventually, a prediction capability of aerodynamic fragmentation (AF), which both currently are severely limited. Experimental research resulted in important main findings. Quantitative experimental data, however, are very difficult to obtain due to extremely small spatial and temporal scales. Individual drops can be investigated by direct numerical simulations (DNS, resolving all relevant spatial and temporal scales of the flow), provided advanced high-resolution discretization schemes and discretely conservative interface models are employed. Efficient computing strategies require tailored data-operation splitting algorithms and multi-resolution representations. When a liquid drop in a gas is impacted by a shock, the shock diffracts and reflects, giving rise to complex wave patterns inside and outside of the drop. Pressure-gradient, baroclinic and surface-tension effects deform the interface. Shear forces along the interface initiate contact-sheet instabilities, whereas capillary instabilities during AF are negligible (surface tension itself is not), as are Richtmyer-Meshkov instabilities due to the high acoustic impedance jump at the interface. Commonly, based on experimental observation, three typical breakup scenarios are distinguished: (i) bag breakup, (ii) sheet stripping, (iii) cata-strophic breakup, which strongly depend on data and flow state uncertainties. A classification of prevalent scenarios in different parameter ranges is highly relevant for applications. Each of the breakup scenarios is characterized by the interplay of different mechanisms, most importantly: (i) Rayleigh-Taylor piercing, (ii) shear-induced entrainment, and (iii) shear-layer instabilities. The objective of the current project is threefold. First, a deterministic DNS method, based on an available high-resolution model for compressible interfacial flows, including effects of surface tension and interfacial friction, needs to be adapted and validated for the applications in this project. Second, a phenomenological analysis of different breakup scenarios with respect to prevalent breakup mechanisms will be performed. A set of numerical simulations are planned whose results allow for clearly assigning breakup scenarios to pa-rameter ranges and for qualification of experimental findings. Third, in a second funding period, we will extend the Mach-number range and assess additional mechanisms that become relevant. Furthermore, uncertainty-propagation tools will be employed for quantifying the confidence.

在快速惯性作用下，以液滴形式分散在气体中的液相的气液界面被破坏称为气动破碎或气动破碎。这类工艺的技术应用广泛，涉及燃料喷雾、熔体、油漆、涂料或生物医学乳剂的二次破碎。工艺优化需要对物理机制的理解，最终需要对气动破片（AF）的预测能力，而这两者目前都受到严重限制。实验研究产生了重要的主要发现。然而，由于空间和时间尺度非常小，很难获得定量的实验数据。如果采用先进的高分辨率离散化方案和离散保守界面模型，单个液滴可以通过直接数值模拟（DNS，解析所有相关的流动空间和时间尺度）进行研究。高效的计算策略需要定制的数据操作分割算法和多分辨率表示。当气体中的液滴受到激波冲击时，激波衍射并反射，在液滴内外产生复杂的波形。压力梯度、斜压和表面张力效应使界面变形。沿界面的剪切力引发接触片不稳定性，而AF期间的毛细不稳定性可以忽略不计（表面张力本身不是），由于界面处的高声阻抗跳变而导致的richmyer - meshkov不稳定性也是如此。通常，基于实验观察，可以区分出三种典型的破碎情景：(i)袋状破碎，（ii）片状剥离，（iii）急转破碎，这三种典型的破碎情景强烈依赖于数据和流动状态的不确定性。对不同参数范围内的流行场景进行分类与应用程序高度相关。每一种破裂情景都以不同机制的相互作用为特征，最重要的是：(i)瑞利-泰勒刺穿，（ii）剪切诱导夹带，（iii）剪切层不稳定。当前项目的目标有三个方面。首先，基于可压缩界面流动的高分辨率模型（包括表面张力和界面摩擦的影响）的确定性DNS方法需要针对该项目的应用进行调整和验证。其次，将对不同的分手情景进行现象学分析，并对普遍的分手机制进行分析。计划了一组数值模拟，其结果允许清楚地将破裂情景分配到pa参数范围并对实验结果进行鉴定。第三，在第二个供资期内，我们将扩大马赫数范围，并评估其他相关机制。此外，不确定性传播工具将用于量化置信度。