Experimental and numerical investigation of Rayleigh-Bénard convection

This thesis presents a combined experimental and numerical investigation of Rayleigh-Bénard convection without and with a background rotation. Rayleigh-Bénard convection, the buoyancy-driven flow induced by temperature gradients, is relevant to a wide variety of both natural phenomena (of which motions in the atmosphere and in the oceans are only the most straightforward examples) and technological applications (like melting of pure metals or flows in turbomachinery). Despite the numerous works on the subject, different aspects of this phenomenon are still unclear or deserving of further investigation. Due to its inherently turbulent nature, the analysis of the flow field makes three-dimensional measurements mandatory to get an unambiguous picture of the underlying rich dynamics. Three-dimensional whole-field velocity measurements are very rare in literature and anyway very recent; in consideration of this, the present work focuses on the application of a state-of-art optical investigation technique, namely the tomographic particle image velocimetry, to the study of such a phenomenon. An experimental apparatus suitable for this purpose is designed and developed. Some technical issues inherent to the optical measurements are extensively addressed; in particular, an innovative camera model is formulated to precisely account for the optical distortions caused by the cylinder sidewall, through which the measurement volume is imaged. In addition to experimental measurements, direct numerical simulations are performed, in which the non-adiabaticity of the lateral wall is accounted for by simulating the presence of the wall itself with its physical properties. The comparison between the experimental and numerical results offers the chance of validating the physical models and computational approaches used in the numerical environment and, at the same time, pointing out unavoidable non-idealities of the experimental setup that make the phenomenon to differ from the canonical problem addressed not only numerically, but also theoretically.