PAMM · Proc. Appl. Math. Mech. 14, 657 – 658 (2014) / DOI 10.1002/pamm.201410312 Boundary Layer Heat Transport in turbulent Rayleigh-Bénard Convection in Air Ronald du Puits 1, * , Christian Resagk 1 , and Christian Willert 2 1 Technische Universität Ilmenau, POB 100565, 98684 Ilmenau 2 German Aerospace Center, 51170 Cologne We study the convective heat transfer in a large-scale Rayleigh-Bénard (RB) experiment which is called the “Barrel of Ilme- nau”. We present the results of flow visualization and Particle Image Velocimetry (PIV) measurements of the near wall flow field in a plane perpendicular to the surface of the heated bottom plate. The experiment was run in a smaller rectangular inset that was placed inside the larger barrel. The Rayleigh number amounts to Ra =1.4 × 10 10 . The aspect ratios were Γx =1 in flow direction and Γy =0.26 perpendicular to the vertical flow plane. The measurements have been undertaken using a 2 W continuous wave Laser in combination with a light sheet optics and various cameras. Due to the slender geometry of the cell, the mean wind is confined in one direction where the Laser light sheet is aligned parallel. The flow was seeded with droplets of 1...2 μm size generated using an ordinary fog machine. Flow visualization as well as the PIV data clearly show the intermittent character of the boundary layer flow field that permanently switches between “laminar” and “turbulent” phases. c  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Many natural or technical flows are associated with a heat transfer from a hot or cold solid surface to a surrounding fluid. However, particularly in case of highly turbulent flows the knowledge about the temperature and the velocity field inside the convective boundary layer, and thus, the predictability of the local heat transfer coefficient is still limited. We study this process in a large-scale Rayleigh-Bénard (RB) experiment which is called the “Barrel of Ilmenau” (see Figure 1, for more details see [1]). It meets two important criteria, a very high Rayleigh number of Ra max = 10 12 – Ra =(βgΔTH 3 )/(νκ), with β – thermal expansion coefficient, g – gravitational acceleration, ΔT – temperature difference, H – thickness of the fluid layer, ν – kinematic viscosity, κ – thermal diffusivity – and a large size of 7.15 m in diameter and 6.30 m in height. The particular advantage of this extra-large facility is the fact that the boundary layer is of the order of tens of millimeters (depending on Ra) which permits a maximum of spatial resolution for all measurements compared to any other RB facility in the world. ∗ Corresponding author: e-mail ronald.dupuits@tu-ilmenau.de, phone +49 3677 691353, fax +49 3677 693683 Laser beam extension heating plate mirrors field of view mean wind cooling plate x y z Fig. 1: Sketch of the large-scale RB experiment “Barrel of Ilmenau”. Fig. 2: Set-up of the flow visualization at the rectangular RB cell inside the large-scale facility. c  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim