Accurate Electric Motor Performance with Multiphysics Simulation

Multiphysics simulation is critical when predicting performance of a design in which many physics interact. ANSYS has a wide array of multiphysics solutions to gain insight into the issues: for example, fluid–structure interactions (FSI) capabilities for thermal as well as fluid force/structure displacement studies for weakly or strongly coupled systems (one-way or two-way). Multiphysics interactions in electric motors include electromagnetic losses and thermal management:

• The magnetic field in the magnetic material heats the material. The heat loss can be predicted by a low frequency simulation tool (in this case, ANSYS Maxwell).
• This heat is diffused and the system is cooled by air, water or both. This thermal management simulation can be simulated by a CFD tool (ANSYS Fluent).
• Thermal management performance impacts the magnetic material temperature, which in turns impacts electric motor performance.

If you conduct a single-physics simulation, you can only assume (but not be certain) the magnetic material temperature which can lead to errors in predicting electric motor performance. In this example, it is as much as 18 percent error.

This view is of a section of an electric motor model including the stator, rotor, magnets as well as the pipe used for water cooling.

ANSYS Maxwell is used to compute the electromagnetic performance of the electric motor. This image shows heat losses in the magnetic materials. The air and water cooling system (not shown here) extracts the generated heat to ensure that the electric motor operates correctly.

In this simulation, ANSYS Fluent is used to compute the temperature of electric motor magnetic material as well as the temperature of the surrounding cooling and cooling fluid (water). ANSYS Maxwell is used to compute heat losses in the magnetic material. The heat losses are defined as the energy source in ANSYS Fluent.

Managing such simulations can be complex if you do not have tools to connect them. ANSYS offers a state-of-the-art solution to this challenge:

• 2-D or 3-D? ANSYS Maxwell low-frequency simulation can be performed in either 2-D or 3-D. Whatever strategy you pursue, you can map heat losses to the 3-D CFD simulation in ANSYS Fluent.
• Steady or unsteady? The time scale of the thermal management simulation is much larger than the electric motor time scale (seconds vs. milliseconds). Simply running a fully coupled unsteady multiphysics simulation is time prohibitive. The solution is to run an unsteady Maxwell low-frequency simulation, time average the heat losses, and perform a steady CFD simulation in ANSYS Fluent.
• How do you easily manage the multiphysics simulation? Passing the information from one physics solver to the other then interpolating the results when needed can be daunting. ANSYS Workbench solves these challenges by automating these complex tasks. Multiphysics simulations can be created simply by dragging and dropping the key simulation tools in the ANSYS Workbench environment window.