Enhancing and Validating Numerical Models for Oil-Jet Cooing on Corrugated Surfaces of Electric Motor Windings

The U.S. DRIVE Electrical and Electronics Technical Team has set a goal for 2025 to achieve a power density of 33 kW/L for electric vehicle (EV) motors. The increase in motor power density is highly dependent on effective thermal management within the system, making active cooling techniques like oil-jet impingement essential for continued advancements. Due to the time and expense of physical experimentation, numerical simulations have become a preferred method for design testing and optimization. These simulations often simplify the motor-winding surface into a smooth cylinder, overlooking the actual corrugated surface due to windings, thus reducing computational resources and mesh complexity. However, the coil's corrugated surface affects flow turbulence and heat transfer rates. This study utilizes three-dimensional Computational Fluid Dynamics (CFD) simulations to investigate the impingement-cooling of an Automatic Transmission Fluid (ATF) jet on a corrugated surface that replicates motor-winding coils of varying diameters. It uses the Volume of Fluid (VOF) method to model multiphase transport, considering how temperature variation affects ATF viscosity. Different wire diameters and inlet jet velocities are accounted for, with the resulting average Heat Transfer Coefficient (HTC) predictions being compared with experimental data from existing literature. The established CFD simulation process provides guidelines for assessing variations in oil-jet cooling such as nozzle size, oil flow rate, impingement angles, and wire diameters found in contemporary EV motor designs. The results from the VOF approach are later compared with those from Smoothed-Particle Hydrodynamics (SPH) to study the differences in performance and accuracy in capturing the impingement and cooling effects.