[论文解读] Experimental study of turbulent thermal diffusion of inertial particles in a convective turbulence forced by oscillating grids

E. Elmakies, O. Shildkrot+3 more|arXiv (Cornell University)|Feb 25, 2026

Particle Dynamics in Fluid Flows被引用 0

一句话总结

该论文在对流湍流中通过一个或两个振动网格驱动，实验研究惯性颗粒的湍动热扩散，结果显示惯性颗粒的聚集更强，并验证有效输运速度的理论预测。

ABSTRACT

We investigate the phenomenon of turbulent thermal diffusion of inertial solid particles in laboratory experiments with convective turbulence forced by one or two oscillating grids in the air flow. Turbulent thermal diffusion causes a non-diffusive contribution to turbulent flux of particles described in terms of an effective pumping velocity directed opposite to the gradient of the mean fluid temperature. For inertial particles, this effective pumping velocity depends on the Stokes and Reynolds numbers. In the experiments, fluid velocity and spatial distribution of inertial particles are measured using Particle Image Velocimetry system, and the temperature field is measured in many locations by a temperature probe equipped with 12 thermocouples. Measurements of temperature and particle number density spatial distributions have demonstrated formation of large-scale clusters of inertial particles in the vicinity of the mean temperature minimum due to turbulent thermal diffusion. In the experiments, the effective pumping velocity resulting in formation of large-scale clusters of inertial particles (having the diameter $10 μm$) is in 2.5 times larger than that for non-inertial particles (having the diameter $0.7 μm$). This is in an agreement with the theoretical predictions.

研究动机与目标

• 在对流湍流中研究惯性固体颗粒的湍动热扩散。
• 描述惯性效应如何改变输运速度和颗粒聚集。
• 在温度层化湍流下比较惯性与非惯性颗粒的行为。
• 量化聚集对雷诺数和斯托克斯数的依赖性。
• 验证 α 和 V_eff 的理论预测与实验室测量的一致性。

提出的方法

• 使用一个矩形对流腔，通过一个或两个振动网格产生对流湍流并产生垂直平均温度梯度。
• 用粒子成像测速（PIV）测量流体速度场，用 12 点温度计探针测量温度。
• 利用两种颗粒尺寸（0.7 μm 和 10 μm）的迈散散射追踪颗粒数密度分布，并将强度与 n 联系起来。
• 对湍动扩散应用稳态平均场框架，V_eff = -α D_T ∇ln T，及 n̄ 演化方程。
• 从测得的 n̄ 和 T 分析 α 和 β，以比较惯性与非惯性颗粒的行为。
• 将实验证据与湍动扩散和涡热摄动的理论表达式联系起来。

Figure 1: Experimental setup with the convective turbulence forced by one oscillating grid (left panel) and by two oscillating grids (right panel): (1) digital CCD camera; (2) rod driven by the speed-controlled motor; (3) oscillating grid; (4) laser light sheet; (5) temperature probe equipped with 1

实验结果

研究问题

• RQ1 在温度分层湍流中，湍动热扩散如何驱动惯性颗粒的大尺度聚集？
• RQ2 斯托克斯数和雷诺数如何影响惯性与非惯性颗粒的有效输运速度和聚集？
• RQ3 在由振动网格产生的对流湍流中，α 和 V_eff 的实验结果是否与理论预测一致？
• RQ4 在相同驱动条件下，惯性颗粒的积累强度相对于非惯性颗粒的相对强度如何？

主要发现

• 惯性颗粒（10 μm）显示更强的聚集，且有效输运速度约为非惯性颗粒（0.7 μm）的2.5倍。
• 惯性颗粒观察到的最大 α 约为 2.5，非惯性颗粒为 α = 1。
• 颗粒在平均温度极小值附近积累，证实了对流湍流中的湍动热扩散。
• α 随垂直雷诺数增加，在单网格情形下从约 1.2 增至 2.4、在双网格情形下从 1.6 增至 2.6。
• 实验结果与关于惯性颗粒相对非惯性颗粒具有增强输运的理论预测一致。

Figure 2: Distributions of the mean velocity field $\overline{U}$ for convective turbulence forced by one oscillating grid (left panel) and by two oscillating grids (right panel). The coordinates $Y$ and $Z$ are normalized by $L_{z}=26$ cm. The mean velocity $\overline{U}$ is measured in cm/s.