Rayleigh-Bénard convective structures in a cylindrical container

In this article we investigate the various convective patterns that appear in a cylindrical container with a diameter 20 times larger than its depth. It turns out that, with a fluid having a Prandtl number of 380, these patterns are disordered and stationary (after a relaxation process). We show that these disordered structures are favoured with respect to regular ones like axisymmetric roll patterns and we demonstrate that the boundary conditions play an essential part in this instability. At last we consider two kinds of defects commonly encountered in these disordered structures and we study them through their velocity field obtained by laser Doppler anemometry. We show that this method enables quantitative comparison with recent theories to be done. J. Physique 44 (1983) 293-301 MARS 1983,