报告人：德国马克斯-普朗克动力学与自组织研究所 Lukas Zwirner博士、Xuan Zhang博士
题 目：Inclined turbulent thermal convection in liquid metals
Rayleigh-Benard Convection (RBC), where a fluid is confined between a hot plate from below and a cold plate from above is a common model system to study convective heat transport. We investigate fluids with very low Prandtl numbers (Pr << 1), i.e. liquid sodium, by conducting experimental measurements as well as direct numerical simulations. Our results show a very good agreement of experiments and simulations and provide a complementary picture of the relationship between the dynamics of the large-scale circulation (sloshing and torsional modes) and the instantaneous heat transport.
Furthermore, we investigate inclined convection, where the RBC cell is tilted by an inclination angle β up to 90° with respect to gravity. In inclined convection we observe an increased heat transport compared to RBC and our results show, that at a certain inclination angle the sloshing and torsional modes are suppressed.
Lukas Zwirner studied physics at the Otto-von-Guericke University of Magdeburg and received his Master of Science in December 2015. For his Master thesis he simulated the chain fountain, using a two-dimensional discrete element method. In April 2016 he started his PhD studies on turbulent heat convection with a focus on the numerical investigation of inclined Rayleigh–Bérnard cells.
题 目: Boundary Zonal Flow in Rotating Turbulent Thermal Convection
Rotating Rayleigh-Bénard convection (RBC) in pressurized sulfur hexafluoride (SF6 in a cylindrical cell of the diameter-to height aspect ratio ½ is studied using finite-volume code Goldfish. The results based on direct numerical simulations (DNS) at Prandtl number 0.8, Rayleigh number 108 to 1010 and Rossby number 0.02 to 50 are presented.
Effects of rotation on the flow structures are investigated in terms of the dynamics of large-scale circulation, local historical temperature signals and global heat transfer. DNS results of the flows at high Rayleigh numbers and moderated to fast rotating rates are compared with the experimental results obtained in the large-scale rotating RBC experiments of SF6 in Uboot of Göttingen. It is found that, a boundary zonal flow (BZF) with a bimodal temperature distribution in local temperature measurements as the signature appears when rotation is fast.
Xuan Zhang received her master in 2013 and doctorate in 2017 from the University of Michigan-Dearborn. Her PhD research was on the numerical investigation of convection in flows of liquid metals subjected to extremely strong magnetic fields. In September 2017, she joined the group at the MPIDS to work on the project of rotating turbulent thermal convection at large Rayleigh numbers.