Tomographic particle image velocimetry of Rayleigh-Bénard convection in a cylindrical sample

This work reports on an experimental investigation of turbulent Rayleigh-Bénard convection in a cylindrical cell using tomographic particle image velocimetry (T-PIV). Differently from other anemometric techniques, which allow measurements of two- or three-component velocities only in selected planes of the flow domain [1], T-PIV provides the complete three-dimensional velocity vector field and thus it is suitable for the analysis of turbulent flows exhibiting a complex dynamics [2]. For the present study, a T-PIV apparatus is specifically developed to investigate thermal convection inside a cylinder of aspect ratio 1/2 filled with water at the Prandtl number Pr = 7 and the Rayleigh number Ra = 2E8. The experimental setup is shown in Figure 1. The top cooling system consists of a water heat exchanger coupled with a Peltier module, while the bottom heating system is made of a copper insert heated by a mica-insulated flat heater. Both temperatures are maintained constant by a high-precision thermoelectric controller which performs a PID control based on continual measurements of the copper and cooling water temperatures (stability< 0.01°C). The laser light is shaped into a cylindrical beam that illuminates the entire cell; four cameras record the light scattered by the seeding particles. Flow modes and flow structures are extracted by applying statistical techniques, such as proper orthogonal decomposition.