3D CHT Simulation of Oil-Cooled Electric Motors: A Comparative Study of Standard and Paperless Designs

Conjugate heat transfer (CHT) analysis of cooling in an electric motor, featuring both the standard and the paperless stator designs, was conducted using the CFD package Simerics-MP+ to assess the predictive accuracy of the numerical simulations. The condition investigated involved the motor running at 14,000 RPM. The high rotor speed was modeled using a novel hybrid approach for mesh rotation to make the problem more tractable. The two immiscible fluids, oil and air were modeled using the interface capturing, volume of fluid (VOF) method. The traditional CHT approach is computationally expensive for electric motor cooling applications due to the heat transfer time scale differences between the fluid and the solid. Temperature changes in solids occur over a much slower time scale owning to their higher thermal inertia compared to fluids. Therefore, we model the fluid and solid domains separately and use a mixed-time scale approach to exchange the heat transfer data between them. The heat transfer analysis conducted here is a quasi-steady state simulation. Numerical results for both the standard and paperless stator design were compared against the thermocouple measurements from test and showed very good agreement.