Temperature Oscillations in Turbulent Mixed Convective Air Flows

We report on measurements of temperature oscillations observed in turbulent mixed convection in a rectangular enclosure. They are correlated to fluctuations and spontaneous reorientations of the large-scale circulations in the flow. Stable temperature configurations, periodic reconfigurations as well as spontaneous reversals and reorientations were detected. We ascribe the observed dynamics of the largescale flow to the interaction between the superimposed shear forces of the forced convective flow and the buoyancy driven flow. Comparison with smoke visualisations allowed to assign the observed temperature distributions to a certain number and configuration of convection rolls. A frequency analysis of the oscillations as a function of the characteristic numbers is conducted revealing a sophisticated dependency of the dynamics of the large-scale flow on Ar, Re or Ra