[論文レビュー] 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被引用数 0

ひとこと要約

要旨：この論文は、対流乱流中の慣性粒子の乱流熱拡散を実験的に調べ、慣性粒子の凝集が強いことと有効ポンピング速度の理論予測を検証する。

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.

研究の動機と目的

• 対流乱流における慣性固体粒子の乱流熱拡散を調べる。
• 慣性効果がポンピング速度と粒子凝集に如何に影響するかを特徴づける。
• 温度が層状になった乱流における慣性粒子と非慣性粒子の挙動を比較する。
• 凝集の Reynolds 数と Stokes 数への依存性を定量化する。
• 実験測定と理論予測 α および V_eff の整合性を検証する。）
• method（方法）
• [
• Use a rectangular convection chamber with one or two oscillating grids to generate convective turbulence and a vertical mean temperature gradient.
• Measure fluid velocity fields with Particle Image Velocimetry (PIV) and temperature with a 12-thermocouple probe.
• Track particle number density distributions using Mie scattering of two particle sizes (0.7 μm and 10 μm) and relate intensity to n.
• Apply the steady-state mean-field framework for turbulent diffusion with V_eff = -α D_T ∇ln T and n̄ evolution equations.
• Analyze α and β from measured n̄ and T to compare inertial and non-inertial particle behavior.
• Relate experimental findings to the theoretical expressions for turbulent thermal diffusion and turbophoresis.

実験結果

リサーチクエスチョン

• RQ1 How does turbulent thermal diffusion drive large-scale clustering of inertial particles in temperature-stratified turbulence?
• RQ2 How do Stokes and Reynolds numbers affect the effective pumping velocity and clustering for inertial vs. non-inertial particles?
• RQ3 Do experimental results for α and V_eff align with theoretical predictions in convective turbulence generated by oscillating grids?
• RQ4 What is the relative strength of inertial particle accumulation compared to non-inertial particles under the same forcing conditions?

主な発見

• Inertial particles (10 μm) exhibit stronger clustering and an effective pumping velocity that is about 2.5 times larger than non-inertial particles (0.7 μm).
• Maximum α observed for inertial particles is approximately 2.5, compared to α = 1 for non-inertial particles.
• Particles accumulate near the mean temperature minimum, evidencing turbulent thermal diffusion in convective turbulence.
• α increases with vertical Reynolds number, rising from about 1.2 to 2.4 (one-grid case) and 1.6 to 2.6 (two-grid case).
• Experimental results agree with theoretical predictions about enhanced pumping for inertial particles relative to non-inertial ones.

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.