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
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2023
Författare
Hamidi, Oskar
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
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.
Beskrivning
Ämne/nyckelord
CFD , CMS , Contamination , Droplets , Film rupture , Multiphase , Road spray , Vehicle aerodynamics , Wind tunnel