Lagrangian particles and particle clusters in large-aspect-ratio turbulent Rayleigh-Bénard convection experiment
Year: 2026
Type: preprint
Abstract: We perform Lagrangian particle-tracking experiments in turbulent Rayleigh-Bénard convection at aspect ratio Gamma = 10, Rayleigh number Ra = 9.3 x 10^7, and Prandtl number Pr = 4.8. Approximately 50,000 neutrally buoyant particles are tracked for durations of up to 150 Kolmogorov times. The resulting trajectories are sufficiently long to capture the mean-square displacement of single particles from the short-time ballistic regime to the long-time diffusive regime. We further analyse Lagrangian velocity structure functions and particle-pair dispersion, both of which exhibit scaling behavior consistent with theoretical expectations in their respective temporal regimes. In the Richardson-like regime, the pair-dispersion exponent exceeds 3, most clearly in the lateral direction. Multi-particle statistics are investigated by analysing particle clouds with initial radii of approximately 8 and 20 Kolmogorov lengths using principal component analysis. The clouds spread more strongly in the lateral directions than in the vertical direction and deform from initially spherical shapes into oblate ellipsoids within approximately 10 Kolmogorov times, revealing pronounced anisotropic dispersion. The dynamics is identified from the particle-connectivity network through a spectral analysis of the graph Laplacian followed by k-means clustering. Furthermore, we examine the probability density functions of all three acceleration components and assess the statistical convergence of their second and fourth moments. The lateral acceleration components are more intermittent than the vertical component, as indicated by their heavier tails. Acceleration statistics conditioned on the bulk region are slightly less intermittent than those obtained over the full measurement volume, which we attribute to the highly intermittent plume-ejection and plume-aggregation events occurring near the walls.
Source: arXiv (Cornell University)
Institution: Technische Universität Ilmenau
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Funders: Freistaat Thüringen, European Commission
Award: G4239725852
OpenAlex ID: W7204952969