Numerical investigation of the flow inside a precession-driven cylindrical cavity with additional baffles using an immersed boundary method

Abstract

In this paper we present a numerical approach to solve the Navier-Stokes equations for arbitrary vessel geometries by combining a Fourier-Spectral method with a direct forcing Immersed Boundary method which allows to consider solid-fluid interactions. The approach is applied to a paradigmatic setup motivated by the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The experiment consists of a fluid filled cylinder rotating about 2 axes which induces a precession driven flow inside the cavity. The cylinder is also equipped with baffles at the end caps with adjustable penetration depth to impact the flow. The numerical details as well as simulation results for the spin-up and precession driven flow in a circular cylinder with additional baffles are presented. The results provide a first confirmation that the use of such baffles in the precession dynamo experiment is a useful way of influencing the flow, allowing more efficient driving without changing the known flow structure too much.

Special topic on precession, nutation, and libration driven flows

“…Qualitatively, the result is very similar to the behavior in the cylinder, and also the degree of symmetry breaking remains relatively small so that the flow is essentially determined by the symmetric large-scale flow. Further numerical investigations by Wilbert et al 22 demonstrate that baffles attached to the inner walls, even of modest inward extension, considerably increase the kinetic energy transferred to the fluid, which may prove necessary to achieve fully developed dynamo regimes in the upcoming experiment at HZDR.…”

Towards synthetic magnetic turbulence with coherent structures

“…The velocity is driven on Fourier modes 1 ≤ k ≤ 3 with the random forcing proposed in [42], which exhibits very low mean cross-helicity and low noise in the time evolution of turbulence bulk quantities. For this purpose we employed the pseudo-spectral code SpecDyn, which was developed in the context of magnetic dynamo action and is tailored for use on modern HPC systems [43,44].…”