Longest P Worth, Oldham Michael J
Department of Mechanical Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3015, USA.
Inhal Toxicol. 2006 Sep;18(10):761-71. doi: 10.1080/08958370600748653.
In order to better understand aerosol dynamics and deposition in the complex flow field of the respiratory tract, both in vitro experiments and numerical modeling techniques have widely been employed. Computational fluid dynamics (CFD) modeling offers the flexibility of easily modifying system parameters such as flow rates, particle sizes, system geometry, and heterogeneous outlet conditions. However, a number of numerical errors and artifacts can lead to nonphysical CFD results. Experimental methods offer the advantage of physical realism; however, parameter variation is often difficult. The objective of this study is to illustrate the use of CFD to enhance the understanding of experimental results. In parallel, the selected experimental results have been used to partially validate the CFD predictions. A specific case study has been considered focusing on 1-mum particle depositions in a physiologically realistic bifurcation (PRB) model of respiratory generations 3-5. Previous experiments in this system report a deposition rate of approximately 0.01%. An in-depth CFD analysis has been employed to evaluate two cases of the empirical model. The first case consists of only the PRB double bifurcation geometry. The second case includes a portion of the experimental particle delivery system, which may influence the entering velocity and particle profiles. To assess the influence of upstream transition and turbulence, each of the two cases considered has been evaluated using laminar and low Reynolds number k-omega approximations. Results indicate that both upstream flow effects and turbulent or transitional flow play a significant role in determining the deposition of 1-mum particles in the model considered. Simulating upstream flow effects and laminar flow was required to match the empirically reported deposition fraction and provided a two orders of magnitude improvement over initial CFD estimates. This study highlights the need to consider the effects of experimental particle generation systems on velocity and particle profiles entering respiratory models. Future work is necessary to investigate the mechanisms responsible for the experimentally observed local deposition patterns.
为了更好地理解呼吸道复杂流场中的气溶胶动力学和沉积情况，体外实验和数值模拟技术都得到了广泛应用。计算流体动力学（CFD）建模具有轻松修改系统参数的灵活性，如流速、颗粒大小、系统几何形状和非均匀出口条件。然而，一些数值误差和伪影可能导致不符合实际的CFD结果。实验方法具有物理真实性的优势；然而，参数变化往往很困难。本研究的目的是说明如何使用CFD来加深对实验结果的理解。同时，所选的实验结果已被用于部分验证CFD预测。已考虑了一个特定的案例研究——聚焦于呼吸第3 - 5代生理逼真的分叉（PRB）模型中1微米颗粒的沉积。此前该系统的实验报告沉积率约为0.01%。已采用深入的CFD分析来评估经验模型的两种情况。第一种情况仅包括PRB双分叉几何结构。第二种情况包括实验颗粒输送系统的一部分，这可能会影响进入速度和颗粒分布。为了评估上游过渡和湍流的影响，所考虑的两种情况均使用层流和低雷诺数k - ω近似进行了评估。结果表明上游流动效应以及湍流或过渡流在确定所考虑模型中1微米颗粒的沉积方面都起着重要作用。模拟上游流动效应和层流是匹配经验报告的沉积分数所必需的，并且比初始CFD估计有两个数量级的改进。本研究强调了需要考虑实验颗粒生成系统对进入呼吸模型的速度和颗粒分布的影响。未来有必要开展工作来研究导致实验观察到的局部沉积模式的机制。
