Windscreen wipers are an integral component of the windscreen cleaning systems of most vehicles, trains, cars, trucks, boats and some planes. Wipers are used to clear rain, snow, and dirt from the windscreen pushing the water from the wiped surface. Under certain conditions however, water which has been driven to the edge of the windscreen by the wiper can be drawn back into the driver’s field of view by aerodynamic forces introduced by the wiper motion. This is wiper drawback, an undesirable phenomenon as the water which is drawn back on to the windscreen can reduce driver’s vision and makes the wiper less effective.
The phenomena of wiper drawback can be tested for in climatic tunnels using sprayer systems to wet the windscreen. However, these tests require a bespoke test property or prototype vehicle, which means that the tests are done fairly late in the development of the vehicle. Furthermore, these results do not provide significant insight into the mechanisms driving the wiper drawback.
In order to better understand wiper drawback a numerical simulation is presented of a configuration known to exhibit this phenomenon. This requires the inclusion into an aerodynamics solver of: moving wipers, a surface film model, and a representation of airborne spray.
Using the results of this simulation, the forces causing the drawback of the water film, along with the mechanism for introducing these forces are studied. Through understanding the driving factors in wiper drawback, it can be avoided earlier in the development cycle.