This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

The importance of mitigating vehicle soiling extends beyond mere aesthetics, as it can significantly impair drivers' vision and the functionality of critical sensors. Addressing this issue early in vehicle development is crucial, necessitating advanced simulation techniques. Magna has developed a hybrid simulation approach that integrates with wind tunnel tests to form a core component of the continuous aerodynamic development process. The first part is a simple complete vehicle soiling simulation. The simulation model developed by Magna utilizes approximately 200 million cells to precisely track boundary layer flow using the low Y+ approach and a Detached Eddy Simulation (DES) turbulence model. This detailed modeling is essential for capturing the near-wall regions accurately, which are crucial for soiling simulations. In this model, the Lagrangian phase, representing particles, is coupled one-way with the Euler phase, representing the air. This allows for a simultaneous evaluation of the aerodynamic and soiling performance of the vehicle. The incremental computational effort, amounting to a 25% increase in simulation time, is justified by the depth of insight gained. This capability facilitates early decision-making regarding the positioning of sensors and cameras, optimization of rear window and light cleanliness, and assessment of soiling on side walls and door handles. Notably, the simulation's ability to detail particle/droplet trajectories offers a significant advantage over physical tests, enabling precise identification of soiling sources and informed development of mitigation strategies. For in-depth analysis of specific regions, the use of submodels becomes necessary. These submodels build on the data from the complete vehicle soiling simulation, focusing on localized phenomena. For example, the soiling and its effect on the side mirror and adjacent side window. Such detailed examinations require an elevated degree of modeling accuracy, introducing two additional Euler phases to the simulation: the fluid film model and the Volume of Fluid model. The fluid film model, a 2-D approximation for wall-bound water, performs well on slightly curved surfaces and sharp convex edges when enhanced by additional detachment models. However, its approximations fail on strongly curved surfaces, like the rear edge of side mirrors. Here, the Volume of Fluid model offers superior accuracy by depicting detailed flow characteristics, albeit with increased mesh and temporal resolution requirements, leading to higher computational demands. Together, these models form a hybrid simulation approach. This method is especially advantageous during early vehicle development phases, where iteration cycles are rapid. In conjunction with the four phases, consideration of the surface contact angle, influenced by material properties, is essential. In summary, Magna's hybrid simulation technique for vehicle soiling, validated through wind tunnel tests, offers a robust and efficient solution during the early stages of vehicle development. It not only aids in maintaining vehicle aesthetics but also ensures the functionality of safety-critical sensors, thus enhancing overall driver safety and vehicle performance.