Large-Scale Particle Image Velocimetry in Convective Airflow

Kurzfassung

We report about the characterization of the flow structure in a large-scale Rayleigh-Bénard (RB) experiment in which a fluid is heated from below and cooled from above. The cylindrical convection cell filled with air has a diameter of 7.1m and a variable height between 0 and 6.30m. At aspect ratio 2 theoretical simulations of the mean velocity field (wind) and the velocity profile measurements predict a transition of a single 2d roll structure into a 3d multi-roll structure. Our stereo PIV measurements at aspect ratio 2 in a light sheet plane of 4m x 3.5m show in agreement with these predictions various 2d and 3d large-scale velocity field structures. Additional PIV measurements in a smaller rectangular convection box show similar coherent flow structures. For seeding the convection flow Helium filled soap bubbles from a multi-channel bubble generator are used. These measurements in the large convection cell, based on large-scale PIV investigations of forced convection flows in large laboratory rooms demonstrate the successful application of highly developed PIV techniques in strongly turbulent 3d flows in measurement areas larger than 3.5m x 3.5m.