Near free-fall oscillatory velocities in liquid metal rotating convection

The geomagnetic field is induced by liquid metal ow inside Earths outer core as a self-excited dynamo. Buoyancy drives the liquid metal flow because the iron rich core is cooling from its primordial state through heat loss to the mantle. The rotation of the Earth and Lorentz forces alter the resulting convective flow. However, since a 3000 km thick rocky mantle hinders our ability to observe core dynamics, the detailed ow topology is still largely unknown. Here we will investigate the effect of rotation on a low Prandtl number thermal convection by means of laboratory experiments and DNS. Therefore, we consider a rotating Rayleigh-Bénard convection setup in an upright cylindrical vessel of aspect ratio Γ = D/H = 2. We investigate supercriticalities in the range of 1 < R < 20 and Ekman numbers 4x10^-4 < Ek < 5 x 10^-6 in liquid gallium at Pr = 0.03. We find that oscillatory convection generates velocity that appear to exceed predictions in steady convection. Multi-modal bulk oscillations dominate the vertical velocity field over the whole range of supercriticalities investigated. Additionally, coherent mean zonal flows and time-mean helicity is found in the rotating liquid metal convection. Thus, we show that these oscillatory flows can be relevant for dynamo action.