Thermal convection in nature or engineering applications often occurs in an environment, whose lateral extent is larger than the vertical one. Experimental velocity or temperature data in such a geometry is rare, in particular, if the Rayleigh number is high. We will present velocity measurements undertaken in a Rayleigh-Bénard cell of aspect ratio \Gamma=3 and a Rayleigh number of Ra=1.4x10^{10}. The working medium was air with a Prandtl number of Pr=0.7. We used Lagrangian particle tracking to measure the global flow field and our measurements covered almost the entire volume of the test section. We captured multiple series of snapshots of the 3d particle positions in the flow and we calculated the Lagrangian flow field from this. The number of snapshots within these series varied between 36,000 and 58,000 with a time step of \delta t=0.1s in between. This choice provided an appropriate temporal resolution of the flow field as well as a very long observation period of up to almost 100 min for the longest run. The figure below shows an example of the Lagrangian particle trajectories in the test section. 

Subject :	:	Oral
Topics	:	Thermal convection
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