Example simulation of E-Motor oil spray cooling with Simcenter STAR-CCM+ Smoothed-Particle Hydrodynamics (SPH) technology

E-Motor oil spray cooling has been a hot topic for a long time. The Finite Volume Method (FVM) is widely used for this application, where different multiphase models can be employed to model various flow regimes in e-motors. For instance, the Lagrangian Multiphase (LMP) model can be used to represent ballistic oil droplets, while Volume of Fluid (VOF) or Large Scale Interface (LSI) models can be used to simulate the oil jets. The Mixture Multiphase (MMP) model is employed to model the oil mist, and a fluid film model can be used to represent the thin oil film. Simcenter STAR-CCM+ also provides different transition models, allowing for the combination of these various multiphase models in a single simulation.

However, there are some well-known challenges when using FVM for this application, such as:

1. Long simulation time: E-Motor oil spray cooling simulations are typically transient and require a significant amount of time (e.g., >700 rotor revolutions) for the oil to reach a steady-state level in the machine.
2. Flow regimes inside the machine are rotation rate dependent. Higher rotation rates result in a greater amount of small, dispersed oil mist. Consequently, the best practices for meshing, time-step selection, and choice of multiphase models, along with their transition model parameters, may vary depending on the motor's rotation rate.

Simcenter STAR-CCM+ version 2402 introduced Smoothed-Particle Hydrodynamics (SPH) technology, which provides a new approach for modeling E-Motor oil spray cooling. 

The main advantages of SPH compared to FVM are:

1. SPH is a mesh-free method, eliminating the need to prepare a watertight geometry as required in FVM. This saves users a significant amount of time for geometry preparation, especially for large industry cases.
2. Easy setup, particularly for applications with moving parts like e-motor or gearbox lubrication. In FVM, a complicated motion model (e.g. sliding interface or overset mesh) is needed to model the motion, whereas with SPH, you only need to specify a rotation speed for the rotating part. There is no need to use overset mesh or sliding interface.
3. Performance is typically better than FVM if the particle size and number of particles are reasonable.

However, the current version (Simcenter STAR-CCM+ V2406) still has some limitations when using SPH for E-Motor oil spray cooling simulation, including:

1. The consideration of aerodynamic forces, which is crucial for high rotation speeds, is not yet possible.
2. Heat transfer modeling with solids (CHT) is not yet supported.

Nevertheless, if you are running cases with low rotation speeds and are primarily interested in analyzing the oil distribution in the motor, SPH may be a good suitable alternative for you. Analyzing low-speed E-motor is also important, since at low speeds, the stator tends to heat up, especially during uphill climbs or start-ups in electric vehicles. This is due to the high torque requirement at low speeds (for constant power), resulting in high electrical losses in the stator and winding.

Attached is an example of using Simcenter STAR-CCM+ SPH method for E-Motor oil spray lubrication simulation. 

https://videos.mentor-cdn.com/mgc/videos/5400/415237be-f296-44e8-bbf9-43e5fd44bc25-en-US-video.mp4