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A full-zone model of a
thermocapillary-driven liquid bridge exposed to a steady, axial magnetic field is
investigated using a global spectral collocation method for low-Prandtl number (Pr)
fluids. Flow instabilities are identified using normal-mode linear stability analyses.
This work presents several numerical issues that commonly arise when using spectral
collocation methods and linear stability analyses in the solution of a wide range of
partial differential equations. In particular, effects such as discontinuous boundary
condition regularization, identification of spurious eigenvalues, and the use of
pseudospectra to investigate the robustness of the stability analysis are addressed.
Physically, this work provides simulations in the practical range of experimentally
utilized magnetic field stabilization in optically heated float-zone crystal growth. A
second-order vorticity transport formulation enables modeling of the liquid bridge
up to these intermediate magnetic field strength ranges, measured by the
Hartmann number (Ha). The thermocapillary driving and magnetic stabilization
effects are observed up to Ha= 500 for Pr= 0.001 and up to Ha= 300
for Pr= 0.02. Prandtl number effects on temperature and flow fields are
investigated within Pr∈ (10−12,0.0667) and indicate that Pr= 0.001 is a
good representation of the base state in the Pr→ 0 limit, at least up to
Ha= 300.
Keywords
magnetic stabilization, thermocapillary, liquid bridge,
linear stability, regularization, pseudospectra