Snow Contamination of Cars: Adhesive Particle Collisions with Exterior Surfaces

Abstract: An ongoing challenge regarding autonomous vehicles is the obstruction of sensors by contaminants on exterior surfaces. This often occurs when driving in harsh weather conditions, where the contaminant can be, for example, water spray, dirt, or snow. Certain regions on a vehicle can have higher rates of deposition compared to others and it is therefore crucial when developing an autonomous vehicle to choose sensor locations that avoid contamination. The present research has aimed to increase the knowledge regarding snow deposition when a vehicle is driving on a snow-covered road. Mathematical models for the cohesive properties of snow and ice have been developed to predict and understand snow deposition on exterior vehicles surfaces. The models were solved analytically or numerically for ice particle collisions with exterior surfaces. Multiple experimental studies were conducted ranging from small-scale experiments on millimeter-sized single ice particle collisions to large-scale climate wind tunnel experiments on bluff bodies. The cohesive properties of snow were measured using an experimental setup for the angle of repose of snow. In summary, this thesis presents results for single ice particle collisions, the angle of repose of snow, and snow contamination on bluff bodies. A regime map for ice particle collisions was developed that predicts a nonlinear dependency between impact velocity and collisional damping. The angle of repose of snow was shown to strongly correlate with temperature, but also with particle size and fall height. Experimental results for the snow contamination of bluff bodies show that snow tends to deposit near aerodynamic wake regions and reattachment regions where the airflow velocities are expected to be low. A numerical model was proposed for the transport of ice particles in a turbulent flow. Simulations that replicate the experiments, show that the numerical model captures the main characteristics of the snow deposition obtained in the experiments.