Experimental Investigation of the Droplet Field of a Rotating Vehicle Tyre 2019-01-5068

The consideration of vehicle soiling in the development process becomes ever more important because of the increasing customer demands on current vehicles and the increased use of camera and sensor systems due to autonomous driving. In the process of self-soiling, a soil-water mixture is whirled up by the rotation of the car’s own wheels and deposits on the vehicle surface. The validation of the soiling characteristics in vehicle development usually takes place in an experimental manner, but is increasingly supported by numerical simulations.

The droplet field at the tyre has been investigated several times in the past. However, there are no published information regarding the physical background of the droplet formation process and the absolute droplet sizes considering the position at the tyre and the behaviour at different velocities. In the numerical self-soiling simulations, this droplet whirl up process is modelled by a non-rotating wheel, where equally sized droplets are injected tangentially from homogenous emitter lines on the tyre surface into the airfield. The impact of the simplifications of this approach on the final result of a self-soiling simulation has not yet been investigated. To achieve a more realistic droplet field, a new approach for the direct simulation of the droplet whirl up process is proposed by the authors in a previous publication.

In order to have a validation basis for the new simulation method and to get a deeper understanding of the droplet formation process, experiments with a detailed analysis of the droplet field have been performed. This study presents the results of experimental investigations of the resulting droplet field for a single rotating tyre in a wind tunnel. The droplet field is exposed by a laser plane and is evaluated with respect to the droplet size and droplet velocity for two different tread designs and tyre speeds.