Large-Scale Flow Visualization and Particle Image Velocimetry in Convective Airflow

Abstract

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 an aspect ratio (A) of 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 A=2 in a light sheet plain of 4m x 3.5m show in agreement with these predictions various 2d and 3d large-scale velocity field structures. For seeding the convection flow Helium filled soap bubbles from a multi-channel bubble generator are used. These measurements in the large convections cell, based on large-scale PIV investigations of forced convection flows in large laboratories demonstrate the successful application of highly developed PIV techniques in strongly turbulent 3d flows in measurement areas larger than 3.5m x 3.5m.