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Droplet collision modeling in multi-dimensional engine spray computations.

机译：多维发动机喷雾计算中的液滴碰撞建模。

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摘要

Drop collisions are critical in determining drop-sizes and mixing processes in multi-phase flows. However, existing spray drop collision models exhibit numerical dependencies and lack comprehensiveness in the outcomes that are considered. The present work attempts both to improve the physical accuracy and to reduce numerical dependencies in spray drop collision calculations.; As a first step, the range of collision outcomes was extended to consider bounce, coalescence and, fragmenting and non-fragmenting separation processes. Fragmentations were modeled assuming that the interacting drops form an elongating ligament that either breaks up by capillary wave instability, or retracts to form a satellite droplet. Comparisons of deterministic model predictions with experiments for colliding mono- and poly-disperse drop streams showed that the outcome of the collision and post-collision characteristics, such as drop-sizes, velocities and spatial distributions of drops, are predicted with acceptable accuracy.; Next, a radius-of-influence of collisional interaction approach was proposed to reduce numerical dependencies. In the method, discrete particle resolution in space was controlled either by manipulating the collision volume, or through selective parcel splitting/merging. To obtain fidelity in the simulations, a mean collision time obtained from the specifics of the collision process was formulated and used. The KIVA-3V CFD code with the new collision model and a gas-entrainment model that corrects the momentum exchange between the drops and the gas was used to simulate a high velocity, non-vaporizing diesel spray. Tests demonstrated adequate insensitivity of the model to numerical parameters.; The improved collision probability and collision outcome predictions were coupled to form a comprehensive collision model, which was used to simulate non-vaporizing diesel sprays produced under conditions relevant to diesel engine common-rail injection systems. Spray penetration results from visualization studies and, drop-size and velocity data from PDPA measurements were used to assess the capability of the model for different injection pressures and various chamber densities. The model gave reasonably good predictions under these conditions. The present improvements to the collision and spray models have increased the fidelity of spray modeling predictions, and are consequently expected to help improve the accuracy of multi-phase flow simulations.
机译：液滴碰撞对于确定多相流中的液滴尺寸和混合过程至关重要。但是，现有的喷雾碰撞模型显示出数值依赖性，并且在所考虑的结果中缺乏全面性。本工作试图提高物理精度并减少液滴碰撞计算中的数值依赖性。第一步，将碰撞结果的范围扩展到考虑反弹，合并以及碎片和非碎片分离过程。在假设相互作用的液滴形成伸长的韧带的情况下对碎片进行建模，该伸长的韧带要么由于毛细管波的不稳定性而破裂，要么缩回以形成卫星液滴。确定性模型预测与碰撞单分散液滴流和多分散液滴流的实验的比较表明，碰撞的结果和碰撞后特性，如液滴大小，速度和液滴的空间分布，均以可接受的精度预测。接下来，提出了一种碰撞相互作用方法的影响半径，以减少数值依赖性。在该方法中，可以通过控制碰撞体积或通过选择性包裹拆分/合并来控制空间中的离散粒子分辨率。为了在仿真中获得逼真度，制定并使用了从碰撞过程的细节中获得的平均碰撞时间。带有新碰撞模型的KIVA-3V CFD代码和纠正液滴与气体之间的动量交换的气体夹带模型被用于模拟高速，非汽化柴油喷雾。试验表明该模型对数值参数足够不敏感。改进的碰撞概率和碰撞结果预测相结合，形成一个综合的碰撞模型，该模型用于模拟在与柴油机共轨喷射系统相关的条件下产生的非蒸发柴油喷雾。来自可视化研究的喷雾渗透结果，以及来自PDPA测量的液滴大小和速度数据，用于评估模型在不同注入压力和不同腔室密度下的能力。在这些条件下，该模型给出了相当不错的预测。碰撞模型和喷雾模型的当前改进提高了喷雾模型预测的保真度，因此有望帮助提高多相流模拟的准确性。

著录项

  • 作者

    Munnannur, Achuth.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 199 p.
  • 总页数 199
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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