Coherent large–scale flow structures in turbulent convection C. Resagk, R. du Puits, E. Lobutova, A. Maystrenko, and A. Thess Dept. of Mech. Eng., Ilmenau University of Technology, 98684 Ilmenau, Germany christian.resagk@tu-ilmenau.de 1 Introduction Thermal convection appears in a large variety of fields like geophysics, met- allurgy, heat exchange, and room air conditioning. A widely used model ex- periment to investigate natural thermal convection is the Rayleigh-B´ enard (RB) cell, a cavity filled with air, heated from the bottom and cooled from above [1]. In the last years there have been a lot of contributions published Fig. 1. Cylindrical experimental facility ”Barrel of Ilmenau” (left) and the rectan- gular cell ”ILKA” (right) about experimental and theoretical investigations of temperature fields and heat transfer in RB convection, but only a few papers about the global ve- locity field [2][3]. Up to now there is no experimental method to analyze the properties of the full three–dimensional flow field in large–scale RB cells. De- spite of the strongly turbulent behavior of the velocity and the temperature field we can find coherent structures in the boundary layers and in the bulk region of the cells.