Rayleigh-Bénard convection
Thermal turbulence is omnipresent and important for the understanding of stars, planets and many technical applications. The canonical experiment for investigating thermal turbulence is Rayleigh-Bénard convection, where a temperature gradient between a warm bottom and a cool lid stimulates a fluid to flow. A typical feature of free convective flows is the formation of large, coherent structures out of small scale thermal turbulence. Convection at very low Prandtl numbers, as found, for example, in the inner core (Pr∼10-2) or in stars (Pr<10-3) has some peculiarities that are due to the very good thermal conductivity. The inertial-dominated flow fields become turbulent rather soon, but are hardly able to strongly influence the temperature field. Experiments with the lowest Prandtl numbers can only be realized with liquid metals and represent a great challenge. In the Department of Magnetohydrodynamics these liquid metal convections and their interaction with magnetic fields are experimentally investigated. With the targeted use of ultrasonic Doppler Velocimetry (UDV) and the contactless CIFT measurement technique, the complex velocity fields in liquid metal can be reconstructed. The speed measurements are supplemented by temporally high-resolution temperature measurements. As a result, the global scales for the heat transport (Nusselt number) and the flow intensity (Reynolds number) can be determined. The liquid metal experiments are complemented by direct numerical simulations (DNS).
Current projects:
- Interaction of liquid metal convection with a horizontal magnetic field
- Interaction of liquid metal convection with a vertical magnetic field (in preparation)
- Liquid metal convection with horizontal temperature gradient
- Turbulent convection in liquid metals with large Rayleigh numbers (DFG-Project, in preparation)
Figure 1: Investigation of the influence of horizontal magnetic fields on liquid metal convection (numerical simulation). The illustrations on the left show the vortex structures (a) and the magnetic field-parallel velocity field (b) with a "weak magnetic field". The illustrations on the right show the influence of a much stronger magnetic field. It is easy to see how the vortex structures align themselves parallel to the magnetic field, whereby the flow becomes quasi two-dimensional. |
Picture 2: Scheme of the tasks sharing between experiment and simulation of liquid metal convection at high Rayleigh numbers. The experiment is part of a DFG project and is currently in the design phase. |
Cooperations:
- FG Strömungsmechanik, Technische Universität Ilmenau
- Laboratory for Flow Control, Hokkaido University, Sapporo, Japan
- Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
- SpinLab, Earth Planetary and Space Sciences, University of California, Los Angeles (UCLA)
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Vogt, T.; Ishimi, W.; Yanagisawa, T.; Tasaka, Y.; Sakuraba, A.; Eckert, S.
Transition between quasi 2D and 3D Rayleigh-Bénard convection in a horizontal magnetic field
Phys. Rev. Fluids 3 (2018) 013503 -
Bertin, V.; Grannan, A.; Vogt, T.; Horn, S.; Aurnou, J.
Rotating thermal convection in liquid gallium: Multi-modal flow absent steady columns
Journal of Fluid Mechanics, submitted -
Zürner, T.; Vogt, T.; Resagk, C.; Eckert, S.; Schumacher, J.
Local Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow
Experiments in Fluids 59 (2018), 3. -
Wondrak, T.; Pal, J.; Stefani, F.; Galindo, V.; Eckert, S.
Visualization of the global flow structure in a modified Rayleigh-Bénard setup using contactless inductive flow tomography
Flow Measurement and Instrumentation (2018) -
Zürner, T., Liu, W., Krasnov, D., & Schumacher, J.
Heat and momentum transfer for magnetoconvection in a vertical external magnetic field
Physical Review E 94(2016), 043108. -
Tasaka, Y.; Igaki, K.; Yanagisawa, T.; Vogt, T.; Zuerner, T.; Eckert, S.
Regular flow reversals in Rayleigh-Benard convection in a horizontal magnetic field
Physical Review E 93(2016), 043109.
References