Complex fluid mechanics theory may explain the movement of tires on wet and slippery roads
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For tire and car manufacturers, it is obvious that they need to be carefully The designed tread pattern does not reduce its adhesion on the road while draining water through the front of the tire.
Unfortunately, there have been few such quantitative experimental studies before. The good news is that with the help of laser imaging technology, the research team conducted in-depth tests in the laboratory environment it built.
As shown in the figure above, tiny fluorescent particles are used to describe the laser irradiation when water is in contact with the tire, so as to visually analyze the phenomenon of water flowing through the front of the tire and through the grooves.
Research picture-2: Different textures Tread indication
For comparison, the quantitative speed measurement of tire treads published earlier was only done with the help of a high-speed camera and rice grains as a water tracer.
After arranging the track in the area above the transparent glass and then immersing it in water, the high-speed camera can observe the general movement of the tire.
However, the disadvantage of this is that the accuracy is not high and the contrast is poor. Because the diameter of the seed is about 1.5 mm, the velocity information in the groove cannot be used for fluid analysis.
Research Picture-1: Single/Three-dimensional Camera illumination scheme
In order to overcome the accuracy problems of traditional schemes, the research team developed a more complex solution. These include the use of fluorescent particles and the use of a piece of laser to illuminate the area to achieve visual observation of the fluid.
It is reported that the diameter of fluorescent particles is only 35 microns, about half of human hair, and the density is close to water.
Research author Damien Cabut said that the first distinguishing feature of the water flow inside the groove is the presence of white filaments or water columns, indicating that there may be gas phase, bubbles or cavitation in this phenomenon.
Research picture-3: Exist in summer Schematic diagram of the bubble column in the tire groove
The researchers pointed out that the mixture of liquid and gas phases in the groove makes the analysis more complicated. In addition, they found eddy currents and turbulence in some grooves. bubble.
The author of the study stated that the number of vortices in the groove may be related to the ratio of the groove width/height of the groove.
Damien Cabut added: “A vortex generation mechanism, or related to the flow around the sharp edge of the tread, has an effect similar to the delta wing phenomenon observed in aerodynamic lift.”
Research Picture-22: Squeeze Effect / A Slot The formation of the second vortex
The study found that when the distance and speed are increased appropriately, the flow structure in the groove is relative to the increase in vehicle speed, which means that it may have an impact on “water skiing”.
However, to understand the formation of vortices and the role of bubbles in the grooves, further research is still needed on the current basis. The details of this research have been published in the recently published AIP “Physics of Fluids” journal.