Investigation Of Turbulent Superstructures In Rayleigh-Benard Convection By Lagrangian Particle Tracking Of Fluorescent Microspheres

We present spatially and temporally resolved velocity measurements of turbulent Rayleigh-Bénard convection (RBC) in a fluid sample of square horizontal cross section with length L = 320 mm and height H = 20 mm, resulting in an aspect ratio of Γ = H/L = 16. The working fluid was water with a Prandtl number of Pr=7 and the Rayleigh-number was set to Ra = 1.1 × 10^6. We seeded the flow with fluorescent polyethylene microspheres that were photographed at a rate of 19 Hz by six cameras. From the images the particle position and their velocity was calculated via the "Shake-The-Box" (STB) Lagrangian particle tracking algorithm. With this approach, we could simultaneously track more than 300,000 particles and hence study the resulting turbulent structures in the Eulerian and Lagrangian frames.