An investigation of road vehicle rear surface contamination and its simulation

Vehicle surface contamination is an important design consideration as it affects aesthetic appearance, driver s vision and the performance of the onboard camera and sensor systems. This work investigates the soiling process and the requirements for credible numerical simulation of the rear surface contamination for two quarter-scale generic car-like bluff bodies, which represent a vehicle type particularly susceptible to this type of contamination. It was shown that the accurate prediction of the mean flow field is a prerequisite for credible soiling estimation. However, modelling the full unsteady behaviour of particle motion with concurrent particle tracking is crucial in order to accurately capture the details of soiling, which is highly unsteady in nature. It was shown that the spray generally entrains into the wake behind the core of the bottom wake vortex and the details of deposition are controlled by the wake structure and the size and orientation of the ring vortex. It was shown that the modelling of secondary spray processes, although computationally expensive, may be important as they tend to change the properties of spray and affect its dynamics. Consideration of realistic boundary conditions, such as the rotating tyres and ground motion was also shown to affect the spray. Wheel rotation increases deposition and the vertical distribution of spray on the base. The ground motion, on the other hand, leads to a wider contamination pattern. An investigation into the tyre spray modelling methods showed that the spray generated behind the contact patch is primarily responsible for the rear surface contamination. Therefore, this study suggested that the tyre spray model currently in use by industrial companies and researchers could potentially be simplified, which would result in a reduced computational effort and would speed up computations of vehicle surface contamination