4.5 Limitations

Many MHD applications involve the simultaneous use of other advanced ANSYS FLUENT capabilities such as solidification, free surface modeling with the volume of fluid (VOF) approach, DPM, Eulerian multiphase, etc. You should consult the latest ANSYS FLUENT documentation for the limitations that apply to those features. In addition, you should be aware of the following limitations of the MHD capability.

• As explained in Chapter  2, the MHD module assumes a sufficiently conductive fluid so that the charge density and displacement current terms in Maxwell's equations can be neglected. For marginally conductive fluids, this assumption may not be valid. More information about this simplification is available in the bibliography.

• For electromagnetic material properties, only constant isotropic models are available. Multiphase volume fractions are not dependent on temperature, species concentration, or field strength. However, sufficiently strong magnetic fields can cause the constant-permeability assumption to become invalid.

• You must specify the applied magnetic field directly. The alternative specification of an imposed electrical current is not supported.

• In the case of alternating-current (AC) magnetic fields, the capability has been designed for relatively low frequencies; explicit temporal resolution of each cycle is required. Although not a fundamental limitation, the computational expense of simulating high-frequency effects may become excessive due to small required time step size. Time-averaging methods to incorporate high-frequency MHD effects have not been implemented.