FreeMHD: validation and verification of the open-source, multi-domain, multi-phase solver for electrically conductive flows

TL;DR

FreeMHD is an open-source, validated computational tool for simulating complex free-surface liquid metal flows under magnetic fields, aiding the design of plasma-facing components in fusion reactors.

Contribution

It introduces a novel, validated open-source MHD solver capable of modeling 3D transient free-surface flows in fusion applications, filling a gap in existing simulation tools.

Findings

Validated against analytical solutions for velocity profiles.

Successfully verified with experimental dam breaking and LM flow cases.

Demonstrated reliability for reactor-scale free-surface MHD flow simulations.

Abstract

The extreme heat fluxes in the divertor region of tokamaks may require an alternative to solid plasma-facing components, for the extraction of heat and the protection of the surrounding walls. Flowing liquid metals are proposed as an alternative, but raise additional challenges that require investigation and numerical simulations. Free surface designs are desirable for plasma-facing components (PFCs), but steady flow profiles and surface stability must be ensured to limit undesirable interactions with the plasma. Previous studies have mainly used steady-state, 2D, or simplified models for internal flows and have not been able to adequately model free-surface liquid metal (LM) experiments. Therefore, FreeMHD has been recently developed as an open-source magnetohydrodynamics (MHD) solver for free-surface electrically conductive flows subject to a strong external magnetic field. The FreeMHD solver computes incompressible free-surface flows with multi-region coupling for the investigation of MHD phenomena involving fluid and solid domains. The model utilizes the finite-volume OpenFOAM framework under the low magnetic Reynolds number approximation. FreeMHD is validated using analytical solutions for the velocity profiles of closed channel flows with various Hartmann numbers and wall conductance ratios. Next, experimental measurements are then used to verify FreeMHD, through a series of cases involving dam breaking, 3D magnetic fields, and free-surface LM flows. These results demonstrate that FreeMHD is a reliable tool for the design of LM systems under free surface conditions at the reactor scale. Furthermore, it is flexible, computationally inexpensive, and can be used to solve fully 3D transient MHD flows.