Laboratory Models of Planetary Core-Style Convective Turbulence

The connection between the heat transfer and characteristic flow velocities of planetary corestyle convection remains poorly understood. To address this, we present novel laboratory models of rotating Rayleigh-Benard convection in which heat and momentum transfer are simultaneously measured. Using water (Prandtl number, Pr similar or equal to 6) and cylindrical containers of diameter-to-height aspect ratios of Gamma similar or equal to 3, 1.5, 0.75, the non-dimensional rotation period (Ekman number, E) is varied between 10(-7)less than or similar to E less than or similar to 3 x 10(-5) and the non-dimensional convective forcing (Rayleigh number, Ra) ranges from 10(7)less than or similar to Ra less than or similar to 10(12). Our heat transfer data agree with those of previous studies and are largely controlled by boundary layer dynamics. We utilize laser Doppler velocimetry (LDV) to obtain experimental point measurements of bulk axial velocities, resulting in estimates of the nondimensional momentum transfer (Reynolds number, Re) with values between 4 x 10(2) less than or similar to Re less than or similar to 5 x 10(4). Behavioral transitions in the velocity data do not exist where transitions in heat transfer behaviors occur, indicating that bulk dynamics are not controlled by the boundary layers of the system. Instead, the LDV data agree well with the diffusion-free Coriolis-Inertia-Archimedian (CIA) scaling over the range of Ra explored. Furthermore, the CIA scaling approximately co-scales with the Viscous-Archimedian-Coriolis (VAC) scaling over the parameter space studied. We explain this observation by demonstrating that the VAC and CIA relations will co-scale when the local Reynolds number in the fluid bulk is of order unity. We conclude that in our experiments and similar laboratory and numerical investigations with E greater than or similar to 10(-7), Ra less than or similar to 10(12), Pr similar or equal to 7, heat transfer is controlled by boundary layer physics while quasi-geostrophically turbulent dynamics relevant to core flows robustly exist in the fluid bulk.