Water contamination of a side view camera monitoring system. Understanding how driving conditions and design features affect dynamics of airborne droplets using CFD and experiments

Abstract

Every year, an estimated 1.3 million lives are lost in traffic collisions. To make driving safer, hazard detecting safety technology is continuously developed, relying on sensors such as cameras to monitor the road. A side view Camera Monitoring System is a tech nology that enables wider rear view vision, revealing the driver’s blind-spot and overall increases visibility in dusk and dawn glaring-conditions. However, the camera is suscep tible to soiling by water droplets, obstructing its lens and hindering its function. This project aimed to increase the understanding of airborne water droplet contamination of a prototype Camera Monitoring System, designed specifically for the project. The theoreti cal droplet dynamics were used to derive a computational model capable of simulating the problem in Simcenter STAR-CCM+ using an Eulerian-Lagrangian approach on a simpli fied aerodynamic body in different driving conditions. Design features of the prototype were evaluated by altering the shape of its glareshield, adding a drainage groove and streamlining the flow at its arm. The designs and bluff body were all tested in Volvo Cars Aerodynamic Wind Tunnel to produce comparable results to the simulations. The project concluded that majority of airborne droplets within the camera’s wake region de form, with some fragmenting into smaller droplets. Subsequently, the droplet drag force would be underestimated if deformation was excluded from the drag model. Drag was also the most significant droplet force, although both gravity and pressure gradient forces became significant for larger droplets, with the latter increasing their response to the flow. Few of the smallest droplets from the primary road spray would soil the prototype, instead airborne droplets would mostly originate from rupturing films of accumulated water at the face’s circumference. Most of the larger droplets would not reach the lens, but deposition size would increase with driving velocity. Grounded droplets were observed migrating to the camera face instead of rupturing in experiments, where they could coalesce with other deposited droplets to form a self-cleaning mechanism, although the likelihood of favoring film ruptures would increase with driving velocity. The simulated ideal drainage groove only permitted the smallest droplets to soil the camera, whilst the real groove would overflow which would permit larger droplets to reach the face, but it did also prevent the migrations. A deeper or wider glareshield would reduce soiling, but when slanted the glareshield would be more susceptible to soiling in both experiments and simulations. Finally, the size of the camera’s wake would decrease when flattening its arm, leading to a reduction in contamination.