Piumini G, Assen M P A, Lohse D, Verzicco R
Physics of Fluids Group and Max Planck Center for Complex Fluid Dynamics, Department of Science and Technology, J.M. Burgers Center for Fluid Dynamics, and MESA+ Institute, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
Max Planck Institute for Dynamics and Self-Organization, Am Fassberg 17, 37077 Göttingen, Germany.
J Fluid Mech. 2024 Sep 20;995. doi: 10.1017/jfm.2024.577. eCollection 2024 Sep 25.
We use three-dimensional direct numerical simulations of homogeneous isotropic turbulence in a cubic domain to investigate the dynamics of heavy, chiral, finite-size inertial particles and their effects on the flow. Using an immersed-boundary method and a complex collision model, four-way coupled simulations have been performed and the effects of particle-to-fluid density ratio, turbulence strength, and particle volume fraction have been analysed. We find that freely falling particles on the one hand add energy to the turbulent flow but, on the other hand, they also enhance the flow dissipation: depending on the combination of flow parameters, the former or the latter mechanism prevails, thus yielding enhanced or weakened turbulence. Furthermore, particle chirality entails a preferential angular velocity which induces a net vorticity in the fluid phase. As turbulence strengthens, the energy introduced by the falling particles becomes less relevant and stronger velocity fluctuations alter the solid phase dynamics, making the effect of chirality irrelevant for the large-scale features of the flow. Moreover, comparing the time-history of collision events for chiral particles and spheres (at the same volume fraction) suggests that the former tend to entangle, in contrast to the latter which rebound impulsively.
我们在立方域中对均匀各向同性湍流进行三维直接数值模拟，以研究重的、手性的、有限尺寸惯性粒子的动力学及其对流动的影响。使用浸入边界方法和复杂碰撞模型，进行了四向耦合模拟，并分析了颗粒与流体密度比、湍流强度和颗粒体积分数的影响。我们发现，一方面自由下落的粒子会向湍流中添加能量，但另一方面，它们也会增强流动耗散：取决于流动参数的组合，前一种或后一种机制占主导，从而导致湍流增强或减弱。此外，粒子手性需要一个优先角速度，这会在流体相中产生净涡度。随着湍流增强，下落粒子引入的能量变得不那么重要，更强的速度波动会改变固相动力学，使得手性效应对于流动的大尺度特征变得无关紧要。此外，比较手性粒子和球体（在相同体积分数下）碰撞事件的时间历程表明，与后者的脉冲反弹相反，前者倾向于缠结。
