Prediction and Modelling of Snow Accumulation on Commercial Vehicles using CFD Simulations and Experimental Methods
Typ
Examensarbete för masterexamen
Program
Automotive engineering (MPAUT), MSc
Publicerad
2021
Författare
Koutsimanis, Dimitrios
Sobieraj, Lukasz
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Snow contamination poses great challenges for the uninterrupted operation of commercial vehicles. The purpose
of this project has been to contribute towards a better understanding of the properties and mechanisms that
drive snow accumulation on commercial vehicles. Computational Fluid Dynamics (CFD) tools and simple
experimental methods were utilized.
Initially, the idea of using only aerodynamic properties to predict snow accumulation was explored. The flow
velocity was used to approximate the snow particle impact velocity and wall shear stress was used as the snow
removing force. However, utilizing flow velocity proved to be challenging given the available tools and using only
wall shear stress did not give accurate predictions. Therefore, a passive scalar was used to approximate snow.
A method combining the passive scalar with wall shear stress was created. The performance of the method was
enhanced by incorporating surface temperature data from field tests. Additionally, snow accumulation was
influenced by surface orientation, i.e. the direction and inclination of the vehicle’s surfaces could either help or
hinder snow packing. The method was validated against infield test data, achieving satisfactory agreement in
most sections of the vehicle. Studying snow-surface interaction was deemed too complicated and therefore it
was decided to substitute snow with ice cubes. Simple experiments were performed to investigate the effects of
temperature and surface material, as well as the influence of adhesion on ice-surface friction. The behaviour of
ice varied significantly depending on temperature and material. The effect of adhesion varied between materials,
contributing to higher values of static friction coefficient around the melting point of ice. At lower temperatures
the effect of adhesion was less significant.
Angle of repose experiments were performed using artificially created snow. The effects of ambient tem perature, surface material and snow fall height were investigated. It was observed that as temperature increased,
larger angle of repose was obtained. Additionally, an increase in fall height resulted in smaller angle of repose.
Differences in the angle of repose were observed also for the different surface materials that were tested. The
possibility of replicating snow with substitute materials was also assessed. It was found that the behaviour of
the tested substitute materials was influenced mainly by the shape and size of their grains.
A multiphase model was developed to study the physics of adhesive ice particles in detail. Discrete Ele ment Method was chosen as the most suitable framework. Data obtained from the experiments were utilized
to allow for a direct comparison between the CFD and test results. Sensitivity analysis was performed for
inter-particle static friction coefficient, tangential restitution and rolling resistance model. It was found that an
increase in inter-particle static friction coefficient resulted in a linear increase of the angle of repose. It was
observed that as the tangential restitution coefficient increased, more time was needed to obtain the final angle
of repose. Because all simulations had the same time limit, the angles of repose obtained in some cases were not
stabilized and prevented the establishment of a trend. In the case of the rolling resistance model, it was found
that the constant torque model resulted in smaller angle of repose compared to the force proportional model.
Beskrivning
Ämne/nyckelord
Computational Fluid Dynamics, Discrete Element Method, Commercial Vehicles, Snow Contamination, Angle of Repose, Adhesion, Multiphase Flow