Experimental Observations of Perturbed Rayleigh-Benard Convection and Analysis of Chaotic Fluid Transport

Abstract

Some of the fluid particles in Rayleigh-Benard convection with perturbed velocity field may be transported chaotically in the Lagrangian description, even when the velocity field seems to be stable in the Eulerian description. In this study, we measure the two-dimensional velocity field of the perturbed Rayleigh-Benard convection by Particle Image Velocimetry (PIV) and detect the invariant manifolds called the Lagrangian coherent structures (LCSs) in order to clarify the chaotic structures of the convection. Especially, we show that LCSs entangle with each other as homoclinic tangles and create some lobes, where fluid particles in the lobes are transported in accordance with the lobe dynamics. In addition, we show that a figure-eight structure appears in the middle of each cell, and that two types of cells with qualitatively different structures appear alternately in the layer when the integration time of the LCSs is increased. Further, we propose a novel perturbed Hamiltonian model that represents some of the experimental results qualitatively.