Gaylard, A., Fagg, M., Bannister, M., Duncan, B. et al., "Modelling A-Pillar Water Overflow: Developing CFD and Experimental Methods," SAE Int. J. Passeng. Cars - Mech. Syst. 5(2):789-800, 2012, doi:10.4271/2012-01-0588.
Water accumulating on a vehicle's wind screen, driven over the A-pillar by a combination of aerodynamic forces and the action of the windscreen wipers, can be a significant impediment to driver vision. Surface water film, or streams, persisting in key vision areas of the side glass can impair the drivers' ability to see clearly through to the door mirror, and laterally onto junctions. Common countermeasures include: water management channels and hydrophobic glass coatings. Water management channels have both design and wind noise implications. Hydrophobic coatings entail significant cost.In order to manage this design optimisation issue a water film and wiper effect model has been developed in collaboration with Jaguar Land Rover, extending the capabilities of the PowerFLOW CFD software. This is complimented by a wind-tunnel based test method for development and validation. The paper presents the progress made to date. The test method, based on installing a rain grid in a climatic wind tunnel, is described. Boundary condition data is extracted to aid CFD model development. This includes: flow similarity assessment against a full scale aerodynamic wind tunnel, water spray flux measurements, screen water distribution, and A-pillar overflow measurements. The CFD method is described and its predictions are compared to experimental data. This includes a simple model to represent the effect of the wiper system. Finally, areas for further improvement in both experimental and computational methods are identified.