Numerical Simulation of Free Surface Liquid Metal Flows using FreeMHD for Nuclear Fusion Applications

FreeMHD is an open source magnetohydrodynamics (MHD) solver, recently developed for free-surface liquid metal (LM) flows under strong magnetic fields. The extreme heat fluxes > 10 MW/m² 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. However, codes to simulate the behavior of free-surface LM under fusion-relevant conditions are not available. Previous numerical studies have mainly used steady-state, 2D, or simplified models for internal flows and have not been able to adequately model free-surface LM experiments. Therefore, FreeMHD, aims to compute incompressible free-surface flows with multi-region coupling for the investigation of MHD phenomena involving fluid and solid domains. The objectives of the project involve validation and verification of FreeMHD to solve fully 3D transient MHD flows. The model utilizes the electric potential formulation to solve the inductionless MHD equations, implemented using the open-source, finite-volume OpenFOAM framework. FreeMHD is validated using analytical solutions for closed channel flows by examining the effect on the closed channel velocity profile and pressure drop while varying the Hartmann number and wall conductance ratio. Experimental measurements of liquid metal depth and velocity are then used to verify FreeMHD for free-surface LM flow on the Liquid Metal eXperiment Upgrade.