Does Turbulent Convection Feel the Shape of the Container?

Temperature and vertical velocity fluctuations are measured in turbulent Rayleigh-Bénard convection for Rayleigh numbers 2×10⁸<R<4×10⁹ in cells with cylindrical and square geometries with approximately unit-aspect ratios. The geometries are constructed such that they have the same height and cross sectional area. We find, very unexpectedly, that both the magnitudes and scalings of fluctuations as a function of R depend strongly on the geometry. This latter result implies a possible nonuniversality in internal fluctuations and poses significant difficulties for existing model descriptions of turbulent convection.