Abstract Dynamics of inertial particles in homogeneous isotropic turbulence is investigated by means of numerical simulations that incorporate the effect of two-way interphase momentum transfer. The continuous phase is solved in the Eulerian approach employing Direct Numerical Simulations (DNS). The dispersed phase is treated using the Lagrangian approach along with the point-particle assumption. The main focus is on computing collision statistics of inertial particles relevant to cloud droplets in typical atmospheric conditions. The vast majority of previous DNS were performed assuming one-way momentum coupling between continuous and dispersed phases. Such simplified approach is adequate only for dilute systems with relatively low mass loading. In this study we investigate the effect of two-way momentum coupling on the kinematic and dynamic collision statistics of the dispersed phase. A number of simulations have been performed at different droplet radii (inertia), mass loading, viscosity and energy dissipation rate. To assess the accuracy of numerical approach the coupling force (exerted by particles on the fluid) was computed using two different techniques, namely particle in cell and projection onto neighboring node. To address the effect of gravity, the simulations have been carried out simultaneously both with and without gravitational acceleration. It has been found that the effect of two-way coupling is significant both for droplet clustering and the radial relative velocity. It turns out that the collision kernel is more sensitive to the particle mass loading when the gravitational acceleration is considered. The collision kernel of settling droplets increases as the droplet mass loading increases. This is direct consequence of larger radial relative velocity. For non-settling droplets the effect of mass loading is opposite, namely, we observe a minor reduction of the collision kernel as the number of droplets increases.

中文翻译：

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湍流调制和重力对粒子碰撞统计的影响

摘要 通过结合双向相间动量传递效应的数值模拟，研究了均匀各向同性湍流中惯性粒子的动力学。连续相在欧拉方法中使用直接数值模拟 (DNS) 求解。使用拉格朗日方法和点粒子假设处理分散相。主要关注计算典型大气条件下与云滴相关的惯性粒子的碰撞统计。绝大多数以前的 DNS 是假设连续相和分散相之间的单向动量耦合而执行的。这种简化的方法仅适用于质量负载相对较低的稀释系统。在这项研究中，我们研究了双向动量耦合对分散相的运动学和动态碰撞统计的影响。已经在不同的液滴半径（惯性）、质量负载、粘度和能量耗散率下进行了许多模拟。为了评估数值方法的准确性，使用两种不同的技术计算耦合力（由流体上的粒子施加），即单元中的粒子和投影到相邻节点上。为了解决重力的影响，模拟是在有和没有重力加速度的情况下同时进行的。已经发现双向耦合的影响对于液滴聚集和径向相对速度都是显着的。事实证明，当考虑重力加速度时，碰撞核对粒子质量载荷更敏感。随着液滴质量负载的增加，沉降液滴的碰撞核也增加。这是较大径向相对速度的直接结果。对于非沉降液滴，质量载荷的影响是相反的，即，随着液滴数量的增加，我们观察到碰撞核略有减少。