On Lagrangian properties of turbulent Rayleigh-Benard convection

Abstract

We report results from Lagrangian particle tracking in turbulent Rayleigh-B\'enard convection experiments in very different experimental setups.Using air (\Pran=0.7) in a $H=1.1$\,m high cylinder of aspect ratio $\Gamma=1$ as well as water (\Pran=7.0) in rectangular cells of heights $H=0.02$\,m ($\Gamma =16$) and $H=0.04$\,m ($\Gamma=8$), we could cover Rayleigh numbers in the range $10^6\le \Ra\le 1.6\times 10^9$. Using neutrally buoyant particles and the \emph{Shake-The-Box} particle tracking algorithm, we could follow up to 500,000 particles over several hundreds of free-fall times. From these data, we determined averaged velocity profiles, the mean square displacement of single particles, the averaged Lagrangian auto-correlation function as well as particle pair dispersion. Comparing these quantities for very different control parameters (\Ra, \Pran, $\Gamma$) enhances our understanding of turbulence in thermally driven convection.