MULTI-PHYSICS SIMULATION IN THE 21st CENTURY.

Email: info@physica.co.uk

[ AERO-ACOUSTICS ]   [ CHEMICALLY REACTING FLOW ]
[ DYNAMIC FLUID-STRUCTURE INTERACTION ]
[ HIGH SPEED IMPACT ]   [ MAGNETOHYDRODYNAMICS ]
[ VARIABLY SATURATED FLOW ]   

Magnetohydrodynamics (MHD)

The interaction of AC or DC electromagnetic fields with conducting fluids has many applications in the metals processing industries. In the processing of metals electromagnetic fields are used in both melting and solidification processes. Such processes essentially involve interactions of electromagnetics, fluid flow, heat transfer, and change of phase. PHYSICA has been developed to address these problems in a single program. The following examples show a sample of our multi-physics calculations.

When the magnetic Reynolds number is not small then the magnetic field is affected by the flow field and vice-versa. In principle, the magnetic field could be calculated by any electromagnetic code and the results exchanged with a CFD code to evaluate the flow field. However, for large problems that are closely coupled, the calculation process will be dominated by the exchange of field data between the magnetic and flow codes. PHYSICA enables the magnetic and flow fields to be calculated in a single code which facilitates the interactions needed to ensure the physical coupling is evaluated accurately and cost effectively.

Electromagnetic stirring of solidifying alloys

Controlled stirring during continuous casting or ingot solidification is perceived as having a beneficial effect on the dendritic structure, etc. This problem is complex as it involves the simultaneous simulation of fluid flow, heat transfer, solidification and/or melting plus the electromagnetic field.

The PHYSICA approach has been applied to the benchmark problem of tin solidification in an annular crucible with a water cooled inner wall and resistance heated outer wall, as illustrated [ IMAGE ]. This setup allowed both free and forced convection scenarios to be configured together with various levels of superheat. A variety of measurements have been reported by Vives and Perry.

The temperature distribution both with [ IMAGE ] and without [ IMAGE ] the magnetic field switched on, together with some comparisons to the experimental measurements can be seen. The temperature fields are quite distinct and compare well with the measurements except at the top of the vessel for the case without the magnetic field. However, here the boundary conditions are unclear and also lack of detail in the actual measurements means that the predictions are probably a better reflection of the actual physical situation. The difference in the temperature fields is driven by the flow fields. These differences are illustrated [ IMAGE ] and show a comparison part way through the solidification process (again compared with experimental data). Note the double vortex in the magnetically driven flow field.

Magnetic levitation

Semi-levitation induction heating is a process used for melting reactive alloys in an inert atmosphere that avoids any contact of the liquid metal with other materials. Alternating magnetic field induces a strong electric current just under the metal surface which eventually melts the treated alloy due to Joule heating. At the same time, the electro-magnetic force of the induced current supports the side of the metal body while the bottom lies on a water-cooled base and remains solid until the process nears its end before finally pouring down through a central hole into the mould.

A reliable computational model can be very useful to engineers for the optimisation of this type of furnace to maximise output and minimise energy consumption while maintaining optimum quality of the alloys.

A mass-conservative mesh-adaptation algorithm has been designed for tracking the shape of the liquid metal. Finite volume formulation in three dimensions is applied to both the flow and the electro-magnetic calculations within the PHYSICA computational environment.

The image [ IMAGE ] shows a typical mesh and instantaneous velocity field (right half of the cross-section).

Electromagnetic braking (EMB) in continuous casting

In the continuous casting of steel process (see [ IMAGE ] for a schematic of the process) electromagnetic fields may be imposed in the inlet jet region in an attempt to dampen the velocity field and hence reduce surface deformation. In this example two electromagnets of equal and opposite polarity are placed in the jet region [ IMAGE ]. The results [ IMAGE ], obtained using PHYSICA, show the effect that imposing the electromagnetic field has on the velocity field and the resulting free-surface deformation.