Turbulente Konvektion in Flüssigmetallen bei großen Rayleighzahlen

Abstract: Turbulent convection in the eutectic gallium-indium-tin alloy (GaInSn) at the very low Prandtl number Pr = 0.03 is investigated in laboratory experiments as well as in direct numerical simulations. Flow measurements with suitable arrays of multiple ultrasonic Doppler sensors and reconstructions of the three-dimensional flow field using magnetic field tomography are used to visualize for the first time the velocity structure both in the regions near the wall and in the center of a cylindrical convection cell at Rayleigh numbers up to Ra = 5x10⁹. The measurements provide for the first time data on the global momentum transport and the long-term behavior of the three-dimensional, large-scale circulation in the cell. The experiments are flanked by massively parallel spectral element simulations focusing on three-dimensional boundary layer dynamics and the influence of non-ideal thermal boundary conditions at the heating and cooling plates on momentum and heat transport. These simulations will also be used to interpret the measured turbulence statistics. The joint investigations set a new milestone for a deeper understanding of turbulent convection at very low Prandtl numbers with its numerous applications in astro- and geophysical flows as well as in engineering systems.

Figure 1: Photo of the experimental setup without thermal insulation (left). Snapshot of the flow structure measured with ultrasonic Doppler velocimetry (right).