Virtual Optimization of Gearbox Oiling - How Reliable are the Results?

Efficient lubrication is critical for gearbox performance and durability. Traditional CFD methods face limitations in simulating oil flow due to complex geometries and moving parts. Smoothed Particle Hydrodynamics (SPH), a mesh-free particle-based method, offers a promising alternative by accurately capturing free surface and multiphase flow dynamics. This article presents a validated simulation methodology for gearbox oiling using SPH. The approach is benchmarked against experimental data from TU Dresden and BMW, demonstrating high accuracy and efficiency. The study highlights the advantages of SPH in modeling complex multiphase flows and its potential to replace physical prototyping in gearbox development.

Source: Niklas Neher (2024), Master Thesis, TU Dresden / BMW, “Validierung mehrerer Mehrphasen-Simulationstools anhand von Resultaten eines Getriebe-Prüfstandes“

Oil distribution experiment vs. simulation

Introduction

Efficient lubrication is essential for the performance and longevity of automotive gearboxes. The goal of modern development is to design on-demand oiling systems that ensure optimal lubrication under all operating conditions while minimizing oil usage and energy losses. To achieve this, advanced simulation methods are required - particularly 3D Computational Fluid Dynamics (CFD) techniques such as Smoothed Particle Hydrodynamics (SPH), that enable the capturing of complex oil flow behaviors while providing fast turn-around times. For the investigations presented here, the commercial solver PreonLab [1] is applied, which is based on the Implicit Incompressible SPH (IISPH) method which is orders of magnitude faster than other explicit SPH-based formulations. It allows for larger numerical step size (CFL=1) compared to traditional weakly compressible formulations. 

Experimental setup

One of the main challenges in validating SPH simulations is the lack of detailed experimental data. To address this, TU Dresden and BMW conducted comprehensive experiments to measure oil behavior in gearboxes [2]. Two test setups were developed (Figure 1).

  1. Riser Pipe Setup: This setup measured the tangential oil throw-off into a vertical pipe at various rotational speeds.
  2. Tangential Oil Catcher Setup: This configuration evaluated oil transport between two meshing gears, capturing the amount of oil thrown off and squeezed through the gear mesh.

Figure 1: Test rig setup 1 ‘Riser Pipe’ and setup 2 ‘Tangential oil catcher

Both setups were simulated using PreonLab and compared with experimental results. The simulations explored the influence of parameters such as particle size and surface mesh resolution on the accuracy of the results. 

The findings showed excellent agreement between simulation and experiment, particularly when multiphase effects (oil-air interaction) were included. Surface mesh resolution had minimal impact on the results, provided a basic level of detail was maintained. Particle size between 0.5 and 1.5 mm yielded the most accurate results, while larger particles do not capture the flow dynamics adequately.

Another key advantage of the PreonLab simulation approach is its reproducibility and computational efficiency. Simulation times remained nearly constant across different surface resolutions, making the method practical for industrial use. This consistency ensures that different users can achieve comparable results, even with varying modeling approaches.

At higher circumferential speeds (above ~8 m/s), the influence of the air phase becomes significant. Including air in the simulations led to substantial improvements in accuracy, while still maintaining efficient turn-around times. For example, simulations with 18 million particles (oil + air) were completed in about 24 hours using GPU acceleration.
 

In the second test case (Tangential Oil Catcher), the simulation closely matched the experimental data (Figure 2). The oil mass collected in the first reservoir (R1) was accurately predicted, while the second reservoir (R2) showed slightly larger deviations—likely due to the small oil volumes and complex flow paths involved.

Figure 2: Validation case tangential oil catcher - Oil mass in container R1 (MPH)

Conclusion

The investigation shown here demonstrates that SPH-based simulations using PreonLab are a powerful and reliable tool for optimizing gearbox lubrication systems. The method accurately predicts the complex fluid behaviors and significantly reduces the need for physical prototypes, thereby accelerating development and lowering costs. The validated simulation framework enables engineers to design efficient lubrication strategies with confidence.

Future work will focus on incorporating thermal effects and further refining the multiphase modeling to enhance simulation fidelity and expanding the method’s applicability.

About the Authors:

M.Sc. Michael Reichl, 
Senior Application Engineer, Advanced Simulations Technologies, AVL Deutschland GmbH

Event recommendation:

DI (FH) Kurt Schierl, 
Team Lead CFD, Advanced Simulations Technologies, AVL Deutschland GmbH

References

[1] M. Ihmsen, J. Cornelis, B. Solenthaler, C. Horvath, M. Teschner, Implicit Incompressible SPH, IEEE Transactions on Visualization and Computer Graphics, vol. 20, no. 3, pp. 426-435, 2014
[2] Niklas Neher (2024), Master Thesis, TU Dresden / BMW, “Validierung mehrerer Mehrphasen-Simulationstools anhand von Resultaten eines Getriebe-Prüfstandes“

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