Spreading characteristics and influence factors of raindrop impact on the vehicle roof-mounted camera protective surface under airflow

In order to understand the dynamic characteristics of raindrops hitting the protective surface of the roof camera during normal vehicle operation, the realizable K-Epsilon turbulence model, volume of fluid method, and liquid film model are employed to simulate the surrounding flow field, self-shape, and dynamic characteristics of the fluid film before and after raindrop impact. Under uniform inflow conditions, the simulation results of the pressure on the isolated camera protection surface, the motion trajectory before collision, and the spreading diameter after collision are verified by wind tunnel tests. A multiphase flow subdomain model of the roof camera protection surface is established to investigate the effects of various single raindrop diameters and distances from the impact surface, as well as the effects of double raindrop arrangements, under the actual incoming flow. As for the single raindrop, reducing the initial raindrop height increases the spreading area and decreases both global and local liquid film thickness. Furthermore, when the initial raindrop diameter is increased by 10%, there is an observed increase in both spread area and liquid film thickness compared to the baseline. As for the double raindrops, the spreading area in the juxtaposition condition is generally larger than that of the seriation condition, with the exception to a slight increase is observed toward the end. Upon the two raindrops fuse completely, the maximum liquid film thickness and the region with large liquid film thickness at the midline are larger in comparison with those in juxtaposition condition.