Characterisation and Variabilities of Sprays Produced by Tyres Rotating on Wet Surfaces

<div class="section abstract"><div class="htmlview paragraph">Understanding the formation and behaviour of sprays and aerosols generated by vehicles traveling on wet surfaces is crucial due to their impact on vehicle soiling, visibility, and autonomous driving. These sprays and aerosols can reduce visibility for other drivers, contribute to traffic accidents, and reduce the operational capabilities of sensors for driving assistance systems and future autonomous vehicles. Despite the critical importance of understanding the physical properties of these sprays and aerosols for the testing and validation of sensors used in environmental perception and recognition, field data on this subject remains limited.</div><div class="htmlview paragraph">The formation and behaviour of these sprays and aerosols are complex. A fraction of the trailing droplets and ligaments originates directly from the tyres, while the remainder is generated upon the impact of the particles ejected from the tyres with the vehicle’s wheel houses and other surfaces, resulting in either coalescence or further disintegration. Aerodynamic forces also significantly influence the formation of these sprays and aerosols. Although experimental studies have investigated the droplet field around rotary atomisers, there is little published information on the droplet size distribution and number density of the spays around wet tyres under real-like conditions.</div><div class="htmlview paragraph">This work aimed to characterise the sprays and aerosols produced by commercial tyres rotating on wet surfaces. Measurements of droplet size distribution, number density, and contrast degradation were conducted under controlled conditions using optical methods and a test rig. The rig allowed for testing with variations in water depth, rotational velocity, and tyre tread pattern, with measurements taken at various distances from the tyre surface.</div><div class="htmlview paragraph">The results indicate that the mean droplet size (arithmetic) correlates with the tyre's rotational speed but is only weakly influenced by water depth or tyre tread pattern. In contrast, the number density is significantly affected by all of these factors, while contrast degradation is influenced, though weakly, by the tested variables.</div></div>