R(refracted)-PIV measurements of water film flow: application to flow under a rolling tire

An analysis of the water flow generated by a tire rolling over a water film has been carried out on an experimental level. The present investigation is focused on a commercial tire with a winter V-shaped complex sculpture. Flow measurements were performed using an optical technique derived from the standard 2D-PIV, the so-called r(refracted)-PIV. Some specific image processing tools have been developed in order to take into account the jitter of the tire location inside the camera field of view when analyzing a set of independent runs. Considering the analysis of the flow either inside the grooves or in front of the tire, different approaches are proposed. On one hand, a geometrical segmentation of the grooves allows a flow analysis inside these tread elements. A characteristic water velocity deduced from measurements performed over a set of independent runs appears to correlate with the position of the segment under consideration along the contact patch area. It has been considered as the hydrodynamic signature of the present tread design. On the other hand, inside the water-bank in front of the tire, an ensemble averaging process of the local velocity is performed to show the influence of groove presence at small scale and the impact of tread design at large scale.