Experimental investigation of the nutation angle's effect on the flow inside a precessing cylinder


Experimental investigation of the nutation angle's effect on the flow inside a precessing cylinder

Kumar, V.; Giesecke, A.; Gundrum, T.; Pizzi, F.; Ratajczak, M.; Anders, S.; Stefani, F.

Precession-driven flows are considered as potential sources of dynamo action on Earth, ancient moon, and some asteroids. At the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a precession-driven dynamo experiment is now being constructed as part of the DRESDYN project. It is a cylinder filled with liquid sodium with a radius of 1 m and a height of 2 m. The cylinder rotates at a frequency of up to 10 Hz and precesses around the second axis at a rate of up to 1 Hz.
To gain a better understanding of the hydrodynamics of a precessing cylinder, a downscaled 1:6 water mockup with the same aspect ratio, rotation, and precession frequency was built. The typical non-axisymmetric Kelvin mode, which initially increases as the precession ratio increases, is alone not suitable for dynamo action in the experiment. However, a secondary axisymmetric mode that appears in a narrow region of the precession ratio was demonstrated to be particularly promising for dynamo action in the sodium experiment.
To predict dynamo behavior for different precession ratios and precession angles, a thorough understanding of the flow structure in the precessing cylindrical vessel is required. For that purpose, we performed a series of precession measurements on the downscaled water experiment with Ultrasonic Doppler velocimetry (UDV) at various precession angles of 60o, 75o, and 90o. We present the effect of precession angle and rotation direction (i.e. prograde or retrograde) on the dominant flow modes, and quantify this behaviour in dependence on the rotation rate, which is parameterized by the Reynolds number Re = ΩcR2/ν, and the precession ratio Po = Ωp/Ωc, where ν is the viscosity and Ωp = 2πfp is the angular frequency of the precession. The experimental results are compared with numerical simulations.

  • Poster
    9th International Symposium on Bifurcations and Instabilities in Fluid Dynamics, 16.-19.08.2022, Groningen, the Netherlands

Permalink: https://www.hzdr.de/publications/Publ-35619
Publ.-Id: 35619