Experimental study of near-wall transport and structures in turbulent Rayleigh-Bénard convection

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The heat transfer between a solid body and a surrounding fluid is a major process in many natural and technical flows. This physical process is studied experimentally in the so-called Barrel of Ilmenau - a large-scale Rayleigh-Benard experiment with a height of eight Meters and a diameter of seven Meters. Since Ludwig Prandtls work on the convective heat transfer, it is well known that the convective heat transfer coeffialpha cient \in the relation Q_k=\alpha A \Delta T (Q_k - convective heat flux, A - area, \Delta T - temperature difference between the solid body and the fluid) depends on the local velocity field adjacent to the surface of the solid body. The characterization of this velocity field is the central objective in the actual project RB-1 within the DFG Research group FOR 1182. Using 3d Laser Doppler velocimetry, simultaneous temperature and velocity measurements at single points and measurements of the planar velocity field using 2D2C Particle Image velocimetry, we found that the velocity field adjacent to the heated (cooled) surface is extremely complex and strongly three-dimensional. Hence, a comprehensive characterization requires a volumetric velocity measurement.