Livi C, Di Staso G, Clercx H J H, Toschi F
Fluids and Flows Group and J.M. Burgers Centre for Fluid Dynamics, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands.
FLOW Matters Consultancy B.V., Groene Loper 5, 5612AE Eindhoven, The Netherlands.
Phys Rev E. 2022 Jan;105(1-2):015306. doi: 10.1103/PhysRevE.105.015306.
The capability to simulate a two-way coupled interaction between a rarefied gas and an arbitrary-shaped colloidal particle is important for many practical applications, such as aerospace engineering, lung drug delivery, and semiconductor manufacturing. By means of numerical simulations based on the direct-simulation Monte Carlo (DSMC) method, we investigate the influence of the orientation of the particle and rarefaction on the drag and lift coefficients, in the case of prolate and oblate ellipsoidal particles immersed in a uniform ambient flow. This is done by modeling the solid particles using a cut-cell algorithm embedded within our DSMC solver. In this approach, the surface of the particle is described by its analytical expression and the microscopic gas-solid interactions are computed exactly using a ray-tracing technique. The measured drag and lift coefficients are used to extend the correlations, based on the sine-squared drag law, available in the continuum regime to the rarefied regime, focusing on the transitional and free-molecular regimes. The functional forms of the correlations for the ellipsoidal particles are chosen as a generalization from the spherical case. We show that the fits over the data from numerical simulations can be extended to regimes outside the simulated range of Kn. Our approach allows to achieve a higher precision when compared with existing predictive models from the literature. Finally, we underline the importance of this work in providing correlations for nonspherical particles that can be used for point-particle Euler-Lagrangian simulations to address the problem of contamination from finite-size particles in high-tech mechanical systems.
模拟稀薄气体与任意形状胶体颗粒之间的双向耦合相互作用的能力，对于许多实际应用都很重要，例如航空航天工程、肺部药物输送和半导体制造。通过基于直接模拟蒙特卡罗（DSMC）方法的数值模拟，我们研究了在均匀环境流中浸没的长椭球体和扁椭球体颗粒情况下，颗粒取向和稀薄度对阻力系数和升力系数的影响。这是通过在我们的DSMC求解器中嵌入切割单元算法对固体颗粒进行建模来实现的。在这种方法中，颗粒表面由其解析表达式描述，并且使用光线追踪技术精确计算微观气固相互作用。测量得到的阻力系数和升力系数用于将基于连续介质区域中可用的正弦平方阻力定律的相关性扩展到稀薄区域，重点关注过渡区域和自由分子区域。椭球体颗粒相关性的函数形式是从球形情况进行推广选择的。我们表明，对数值模拟数据的拟合可以扩展到克努森数（Kn）模拟范围之外的区域。与文献中现有的预测模型相比，我们的方法能够实现更高的精度。最后，我们强调这项工作在为非球形颗粒提供相关性方面的重要性，这些相关性可用于点粒子欧拉 - 拉格朗日模拟，以解决高科技机械系统中有限尺寸颗粒污染的问题。
