Planetary Science Seminar spring-2018

The magnetic fields of planets are generated and sustained by fluid motions in their electrically conducting liquid metal interiors. The key characteristics of such flows, thought to be governed to leading order by rapid rotation and turbulent convection, are not well understood at present. Our new laboratory device, ‘NoMag’, is designed to span a wider and more extreme range of parameters than previously studied, thus allowing us to explore essential features of rotating convection in a setting similar to that of core flows, i.e. one that is both rapidly rotating and highly turbulent. Specifically, ‘NoMag’ is constructed to simulate a local, polar parcel of planetary core convecting fluid under the influence of axial rotation and buoyancy forcing. As such, a cylindrical geometry is constructed with a fixed diameter of D ≈ 60 cm and heights ranging between H ≈ 5 cm to H ≈ 185 cm. Using this device, we explore the properties of rotating convection in water, with Ekman numbers (viscous diffusion/Coriolis force) ranging between E ≅ 3×10−8 (i.e. rapidly rotating) to E ≅ 10−3 (i.e. weakly rotating) and Rayleigh numbers (thermal buoyancy/ thermal and viscous diffusion) between Ra ≅ 105 (i.e. weakly convecting) to Ra ≅ 1013 (i.e. turbulently convecting). We utilize laser doppler velocimetry (LDV) to obtain point measurements of bulk convective velocities, resulting in measured Reynolds numbers (inertia/viscous diffusion) ranging between Re ≅ 102 to Re ≅ 5 × 104 , with the onset of turbulence occurring near Re ∼ O(103 ). For the first time, we couple velocity and heat transfer measurements by the simultaneous collection of temperature time series at the fluid boundaries and at multiple locations within the fluid bulk. In this talk, I will present recent experimental results using our H ≅ 20 cm tall tank that test inevitably coupled heat transfer and convective velocity scaling predictions relevant to rapidly rotating systems.