Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force.
Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force.
复制标题
均匀各向同性湍流中非重惯性粒子的增强沉降：压力梯度和巴塞特历史力的作用。
DOI：
10.1103/physreve.95.023106
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发表时间：
2017
影响因子：
2.4
通讯作者：
F. Toschi
中科院分区：
文献类型：
--
作者：
Van Hinsberg;H. Clercx;F. Toschi
斯托克斯阻力和重力通常足以描述亚柯尔莫哥洛夫尺度（或点状）重粒子在湍流中的行为，特别是当粒子与流体的密度比ρ p/ρ f ≥ 10^{3}（ρ p和ρ f分别为粒子和流体的密度）时。一般来说，对于较小的颗粒-流体密度比，特别是对于ρ_{p}/ρ_{f}<$10 ^{2}，情况并非如此。在这种情况下，压力梯度力、附加质量效应和Basset历史力也起重要作用。在这项研究中，我们专注于了解的作用，这些额外的力量，所有的流体动力学的起源，在湍流中的颗粒沉降。为了定性地阐明这种粒子在均匀各向同性湍流中的复杂动力学，我们首先关注这种粒子在单个涡流的流场中沉降的情况。在探索了这个简化的情况后，我们将分析扩展到均匀各向同性湍流。在一般情况下，我们发现，压力梯度力导致的沉降速度下降。这可以通过以下事实定性地理解，即该力防止颗粒扫出涡流，这是一种称为优先扫掠的机制，其导致增强的沉降。此外，我们发现，Basset历史力可以增加和减少增强沉降，这取决于粒子的斯托克斯数。最后，非线性斯托克斯阻力的作用进行了探讨，证实它会影响惯性颗粒在湍流中的沉降，但在本研究中使用的参数设置仅以有限的方式。
The Stokes drag force and the gravity force are usually sufficient to describe the behavior of sub-Kolmogorov-size (or pointlike) heavy particles in turbulence, in particular when the particle-to-fluid density ratio ρ_{p}/ρ_{f}≳10^{3} (with ρ_{p} and ρ_{f} the particle and fluid density, respectively). This is, in general, not the case for smaller particle-to-fluid density ratios, in particular not for ρ_{p}/ρ_{f}≲10^{2}. In that case the pressure gradient force, added mass effects, and the Basset history force also play important roles. In this study we focus on the understanding of the role of these additional forces, all of hydrodynamic origin, in the settling of particles in turbulence. In order to qualitatively elucidate the complex dynamics of such particles in homogeneous isotropic turbulence, we first focus on the case of settling of such particles in the flow field of a single vortex. After having explored this simplified case we extend our analysis to homogeneous isotropic turbulence. In general, we found that the pressure gradient force leads to a decrease in the settling velocity. This can be qualitatively understood by the fact that this force prevents the particles from sweeping out of vortices, a mechanism known as preferential sweeping which causes enhanced settling. Additionally, we found that the Basset history force can both increase and decrease the enhanced settling, depending on the particle Stokes number. Finally, the role of the nonlinear Stokes drag has been explored, confirming that it affects settling of inertial particles in turbulence, but only in a limited way for the parameter settings used in this investigation.