Modelling the Effect of Spray Breakup, Coalescence and Evaporation on Vehicle Surface Contamination Dynamics

Paper #:
  • 2018-01-0705

Published:
  • 2018-04-03
Abstract:
Vehicle surface contamination is an important design consideration as it affects drivers’ vision and the performance of on board camera and sensor systems. Previous work has shown that eddy resolving methods are able to accurately capture the flow field and particle transport, leading to good agreement for vehicle soiling with experiments. What is less clear is whether the secondary break-up, coalescence and evaporation of liquid particles play an important role in spray dynamics. The work reported here attempts to answer this and give an idea of the computational cost associated with these extra physics models. A quarter scale generic SUV model is used as a test case in which the continuous phase is solved using the Spalart Allmaras Improved Delayed Detached Eddy Simulation model. The dispersed phase is computed concurrently with the continuous phase using the Lagrangian approach. The TAB secondary break-up and the stochastic O’Rourke coalescence models are used. The spray’s rate of evaporation is calculated based on the relative humidity encountered on a typical October day in Britain. The secondary break-up model is found to be redundant, possibly due to the properties of spray. The coalescence model predicts high coalescence of particles close to the injection point and improves agreement with experiment, although at a very high computational cost. Including evaporation removes small particles from the simulation, this reduces overall contamination but also changes the soiling pattern due to changing the size distribution. This suggests that evaporation may need to be considered or controlled for, when predicting vehicle soiling.
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