Dynamics of thermal plumes in turbulent mixed convection studied with combined Particle Image Thermometry and Velocimetry

Kurzfassung

The dynamics of thermal plumes and their abundance is investigated in mixed convection in a cuboidal sample. The working fluid is air at ambient pressure. Combined Particle Image Thermography (PIT) and Particle Image Velocimetry (PIV) is conducted in a horizontal layer close above the bottom thermal boundary layer. The fingerprints of sheet-like plumes and those of the stems of mushroom like plumes are visible in the instantaneous temperature fields. A study of temperature PDFs reveals, that the distributions can be described by a sum of two Gaussian distributions. Analysing the ratio of the probabilities P_2/P_1 reveals a sudden change at a critical Ra_c. Here P_1 denotes the abundance of fluid temperatures imprinted by the bulk flow, while P_2 represses the abundance of temperatures ascribed to warm thermal plumes. Accordingly, P_2/P_1 is a measure for the plume fraction in the measurement plane.Please see our new paper: Schmeling et al., DOI: 10.1007/s00348-015-1981-z, Exp. Fluids (in press)