caa a22 4500 606197370 CHVBK 20210128100929.0 cr unu---uuuuu 210128e20150601xx s 000 0 eng 10.1007/s00348-015-1981-z doi (NATIONALLICENCE)springer-10.1007/s00348-015-1981-z Measurements of the dynamics of thermal plumes in turbulent mixed convection based on combined PIT and PIV [Elektronische Daten] [Daniel Schmeling, Johannes Bosbach, Claus Wagner] The dynamics of thermal plumes and their abundance is investigated in mixed convection in a cuboidal sample with respect to the characteristic numbers. The parameter range spans $$Ra=1.0{-}3.2\times 10^8$$ R a = 1.0 - 3.2 × 10 8 , $$Re=0.5{-}1.7\times 10^4$$ R e = 0.5 - 1.7 × 10 4 and $$Ar=1.1{-}7.6$$ A r = 1.1 - 7.6 . Combined particle image thermography and particle image velocimetry is conducted in a horizontal layer close above the bottom thermal boundary layer. This combination of measurement techniques, using thermochromic liquid crystals as tracer particles, which is novel for air flows, allows for simultaneous measurement of temperature and velocity fields. Details of the measurement technique are published in Schmeling et al.(Meas Sci Technol 25:035302,2014). 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 well described by a sum of two Gaussian distributions. Analysing the ratio of the probabilities $$P_2/P_1$$ P 2 / P 1 reveals a sudden change at a critical Ra c ≈2.3×108. Here, $$P_1$$ P 1 denotes the abundance of fluid temperatures imprinted by the bulk flow, while $$P_2$$ P 2 represses the abundance of temperatures ascribed to warm thermal plumes. Accordingly, $$P_2/P_1$$ P 2 / P 1 is a measure for the plume fraction in the measurement plane. The change occurs in the $$Ar$$ A r regime $$2.7\,\lesssim\, Ar\,\lesssim\, 3.3$$ 2.7 ≲ A r ≲ 3.3 , in which the interaction of buoyancy-induced large-scale circulations with the wall jet of the incoming air results in an instability reported already by Schmeling et al.(Exp Fluids 54:1517,2013). A combined evaluation of the temperature and velocity fields reveals a change in the horizontal heat fluxes at $$Ar\approx 2.7{-}3$$ A r ≈ 2.7 - 3 . Furthermore, the total amount of heat transported in x direction within the measurement layer increases with $$Ra$$ R a in bulk-dominated regions, while it stays almost constant for plume-dominated ones. Springer-Verlag Berlin Heidelberg, 2015 Schmeling Daniel German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut Bosbach Johannes German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut Wagner Claus German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut Experiments in Fluids Springer Berlin Heidelberg 56/6(2015-06-01), 1-20 0723-4864 56:6<1 2015 56 348 https://doi.org/10.1007/s00348-015-1981-z text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-1981-z text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Schmeling Daniel German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut NATIONALLICENCE 700 1- Bosbach Johannes German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut NATIONALLICENCE 700 1- Wagner Claus German Aerospace Center, Bunsenstraße 10, 37073, Göttingen, Germany aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/6(2015-06-01), 1-20 0723-4864 56:6<1 2015 56 348