External Water Management

Engineering Goals

One key objective of External Water Management (EWM) is to enhance driver comfort and safety by effectively managing water flow around the vehicle. Common regions of interest for EWM analysis include the A-pillar, side windows, and side mirrors. To perform this analysis in a multi-physics environment with specific requirements for each department involved in car development (acoustic, aerodynamic, structural, etc.), a validated virtual wind tunnel is essential for faster vehicle development cycles. Our multiphase methods for EWM simulation combine a thin film model on the vehicle surface, coupled with Lagrangian particles (rain droplets) and the surrounding airflow (external aerodynamics). This integrated approach enables accurate and efficient analysis of water flow behavior under various conditions, ultimately optimizing vehicle design and performance.

Coupling Methods

The coupling between the thin film model, Lagrangian particles, and primary airflow can be activated when necessary. While this increases CPU cost, it ensures the most accurate results in certain scenarios. The decision to use coupling depends on a solid understanding of the physical problem being modeled. A typical example where strong coupling is required is the study of rain impact on the side mirror glass, where the trajectory of the particles is directly influenced by the transient mirror wake.

Film Detachment Model

ICON’s film detachment model captures various physical phenomena that occur when the film exceeds a critical thickness. These include film separation due to substrate curvature, gravity-induced dripping, edge-induced shedding, and wave stripping. The integration of these different film re-entrainment models enables accurate prediction of rain impingement across the entire vehicle surface, providing a comprehensive approach to managing water flow behavior in EWM simulations.

Wiper Model

The wiper motion plays a crucial role in the development of the water film over the windshield and side windows. ICON’s wiper model uses a parametric representation of real wiper geometry, combined with the Immersed Boundary Method (IBM), offering a faster simulation compared to traditional dynamic mesh approaches with real wiper geometry. This efficient method reduces the additional time required for a simulation with wipers to less than 10% compared to one without, making it an attractive solution for industrial applications where speed and accuracy are key.

Virtual Mesh

To simulate surface film development with iconCFD, a one-cell layered mesh is first created by extruding the vehicle surface. However, this physical mesh extrusion can sometimes result in poor-quality cells, particularly for complex or under-refined vehicle surfaces. Over-refining the surface mesh to capture small geometric details can help achieve a successful extrusion, but it often comes at the cost of unnecessarily refining the primary mesh. To eliminate this resolution constraint, ICON introduces a novel method that virtually extrudes the vehicle surface while perfectly preserving the shape of the substrate surface mesh. The virtual mesh is essentially a copy of the surface mesh, with virtual cells approximated by the discrete faces of the surface when the virtual extrusion thickness is close to zero.

Reliable Soiling Predictions

ICON maintains strong collaboration with OEMs to understand their needs and continuously improve their methodology, achieving higher accuracy in delivered results while reducing simulation time. In this context, all functionalities used in EWM simulations are rigorously validated on fully detailed car geometries with climatic wind tunnel data. These validations ensure the reliability of soiling predictions and their relevance to real-world conditions. Examples of such validations can be found in the following publication links: [1], [2].