Large-scale reorientation in cubic Rayleigh–Bénard convection measuredwith particle tracking velocimetry

Kurzfassung

Three-dimensional velocity fields of a large-scale reorientation in turbulent Rayleigh–Bénard convection at Ra = 2.5 · 10 9 in a 300 mm cubic water cell are measured using particle tracking velocimetry. Reorientations are rare events occurring about once every three days in our setup, involve the large-scale circulation switching between cell diagonals. The dominant flow structures of the reorientation are extracted from the measurement data using POD supported by symmetries of the cubic cell to mimic long time series of reorientation events. The decomposition reveals degenerate mode pairs. The first six modes of the decomposition account for about 70% of the total energy and contain the major coherent structures. Modes 1-3 reflect the orientation and dynamics of the large-scale circulation, and modes 4-6 provide the orientation and dynamics of the corner circulations. A pure Y roll structure is observed in the middle of the reorientation event.