March 6 - 8, 2017 | Berlin
LEADING ENGINEERING SIMULATION CONFERENCE
In designing the cleaning system for the front wind screen of a car, many aspects of functionality as well as aesthetics are considered. A good design should ensure full coverage of the wind screen with wiper liquid, with subsequent complete removal of liquid and dirt. This should be done with a minimum consumption of liquid, without sloshing liquid over the A-pillar, leaving runnings or pulling liquid back onto the screen after wiping. It should also be noiseless and invisible when not in use.
CFD provides a simple option to test and to visualize the outcome of various alternative designs and spray/wiping patterns, allowing an early detection of potential problems and creating better designs faster.
The model set-up at FS Dynamics in collaboration with Volvo Cars Corporation is based on an unsteady RANS, in which wipers are rotating and morphing to fit the curved wind screen. On the resulting moving geometry, Lagrangean spray injectors are introduced to represent the cleaning system. In some modern systems, injectors are located on the wiper arms - hence the injectors can also be in translating and rotating motion.
Droplets interact with air flow and impinge on the wind screen, forming a liquid film. Film is interacting with air and wipers. In thick regions of the fluid film, film model may transition to a VoF representation.
In the full model, the STAR-CCM+® simulation is coupled to a FEM-model, allowing for wiper rubber deformation from movement and wiper arm spring-loading.
Results from the model implementation corresponds well to phenomena observed in VCC test facilities; among data available for the customer are liquid coverage, amount of liquid in pull-back from A-pillar, aerodynamic forces on wipers and possible wiper lift-off zones.