Thermal analysis of electric devices methods comparison benefits

Coupling Flux FEA to AcuSolve CFD solution – Thermal Analysis of Electrical Equipment

Vincent Marché

If you want to have more accurate results, the use of CFD analysis is the solution. With CFD code, the main benefit is that there is no more assumption on the exchange coefficients, you just represent the different elements of your motor, with for instance a fan on the shaft, a cooler with a velocity for the liquid, … It helps a lot in order to understand where is the flow, and to better understand critical areas where focus should be on to improve thermal exchange.

The method has been applied on the Prius like motor using Flux 3D and AcuSolve®. The model includes not only the rotor and the stator, but also the casing.

Multiphysics co-simulation Motor B color shade Flux 3D

Motor with the casing and B color shade in Flux 3D

From Flux computation, for the chosen working condition at 900 rpm, we will extract average losses for magnet (due to eddy current), in coils (Joule losses), iron losses in stator and rotor. These values are nodal values corresponding to average losses over one electrical period. Dedicated menus have been developed in order to compute directly these values.

Multiphysics co-simulation Eddy current losses in magnet and iron losses in stator

Eddy current losses in magnet and iron losses in stator


Once the losses are computed in Flux, we can export directly a file in a format that can be read by AcuSolve in Nastran format.

In AcuSolve, the geometry of the motor has to be described as well. In the specific case of this motor, the cooling is done with an external coolant, plus the use of oil in part of the casing. The different solid components are described.

Multiphysics co-simulation Motor Solid components

Solid components of the motor


AcuSolve can then be used in order to determine the behaviour of the fluid surrounding the solid components. Rotational effects are considered. Convection on outer surface can be determined. The losses imported from Flux can be read directly, with the possibility to scale, shift or rotate if periodicity is present. The total heat load in watts can also be applied (on coils for instance). A coolant liquid enters and exit with an external water jacket to help cool the motor at 35°C and 2.4 Gal/min. The rotation of the rotor is also taken into account by modifying fluid region adjacent to it.


The results allow to understand the flow in the water jacket, and also the temperature distribution in the different elements. There is an increase of 5 degrees between the input and the exit of the water jacket.

Flow in the external water jacket computed in AcuSolve

Flow in the external water jacket computed in AcuSolve

The temperature on the casing is shown on the next figure:

Motor Temperature distribution analysis AcuSolve

Motor Temperature distribution analysis AcuSolve

The main benefit is a better understanding of the flow inside and around the motor.




Thus we have seen that different methods are available in order to estimate the thermal behavior of electric motors. Each method can be used at different level of the motor design. The equivalent model is interesting at the early design stage in order to check basic working points, or duty cycles. The solving time is fast, allowing parametric design. When more accuracy is required, using finite elements is a good idea, in order to have a better knowledge of losses (iron losses , eddy current losses), and their impact on thermal analysis. The rise of temperature in different areas is also easier to understand and to follow with animation for instance.  Then if designers want more accuracy, or to better understand the flow, they can combine FEA magnetics with CFD code. It takes more time to create projects and for the solving time. The use of distribution of computation allow decreasing dramatically the solving time.

Thermal analysis of electric devices - Methods comparison applications

Thermal analysis of electric devices – Methods comparison


Learn more about Flux FEA and AcuSolve CFD analysis


A post by Patrick Lombard – Lead Application Specialist EM Solutions – Altair

Vincent Marché

About Vincent Marché

Vincent Marché graduated first in electronics, and then went on to refine his skills at business school. After more than 10 years in the industry, working on product marketing and sales of sensors, switches and electronic devices, he fell into a melting pot called electrical engineering simulation. Supporting FluxTM electromagnetic simulation software since 2009, he is passionate about the large fields of applications addressed by simulation tools and the application expertise of the users. He is constantly looking for solutions that address the innovation needs of electrical engineers. Since the recent acquisition of Cedrat by Altair, he manages the promotion of electromagnetic applications, electrical engineering and e-Mobility.