Oscillating flow in liquid metal vertical convection under the influence of a horizontal magnetic field

The effect of a horizontal magnetic field on heat transport and flow structures in vertical liquid metal convection (Prandtl number Pr ≈ 0.03 ) is investigated experimentally. The experiments are carried out for Rayleigh numbers in the range of 1.48 × 10⁶ Ra 3.54 × 10⁷ and Chandrasekhar numbers in the range of 2 × 10² Q 1.86 × 10⁶ , as well as for the non-magnetic case ( $Q=0$ ). Measurements of the heat transport show a rise in the Nusselt number at low and moderate magnetic field strengths up to an optimum value of Q , before a further increase in the magnetic field leads to a decrease in the transport properties. By applying simultaneous velocity and temperature measurements, we are able to identify three different oscillatory flow regimes for 10⁻⁵< Q/Ra < 0.5 and assign them to the respective heat transfer characteristics. In the range 10⁻⁵> Q/Ra> 10⁻³ , first evidence of a transition to anisotropic flow structures caused by the magnetic field is visible. Two strongly oscillatory regimes are identified, where the energy is either distributed around a dominant frequency ( 10⁻³> Q/Ra> 10⁻² ), or strongly concentrated on a single frequency ( 10⁻²> Q/Ra> 0.5 ). The dominating frequency increases with the Rayleigh number according to Ra0.71± 0.02 . This flow structure based regime separation correspond to changes of both the heat transfer through the Nusselt number and mass transfer through the Reynolds number.