Superstructures in turbulent thermal convection in slender cells*

The large scale circulation (LSC) is one of the most important features in turbulent natural thermal convection. It is self-organized, has its own complicated dynamics and plays a key role in the global heat and momentum transport in convective systems. In this study, we analyze the LSC properties in turbulent Rayleigh--Benard convection and inclined convection of small-Prandtl-number fluids in slender geometries (cylindrical containers of the diameter-to-height aspect ratios smaller than one). We investigate in detail the structures of the so-called single-roll and multiple-roll LSCs, their strength and path lengths and their relation to the strength of the volume-averaged heat transport in the system. The problems of the LSC extraction in experiments and numerical simulations and interpretation of the different LSC modes will be also discussed.