What is it about?
Cars with "blunt" rear ends tend to pick up dirt from the spray generated by their rear wheels. This work takes the simplest representation of this problem, a simple one-box geometry and a spray, and looks at the basic mechanisms and lessons for numerical simulation of this problem.
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Why is it important?
The role of the lower part of the wake vortex is very clearly identified, in capturing spray and advecting it to the rear surface. We have also discovered that the pattern of spray deposition on the rear surface of a bluff body changes little with time (though it gets thicker). This means that we can compare the relative distributions obtained using simulations with longer-period experiments. Hence computational fluid dynamics offers a viable approach to investigating this problem. We also show that the deposition process is linear with time, for the rear surface as a whole. This means that the rate of deposition could be a useful metric comparing different configurations.
Perspectives
I think that the use of simple geometric forms to investigate the fundamentals of this problem has been overlooked. This is a commonly used approach in vehicle aerodynamics and has provided many insights. This work is the first basic step in using this approach combined with scale-resolving CFD. The simulations provide an excellent representation of the vehicle wake, which provides confidence in the spray-deposition part of the work. The linearity of the process and the stability over time of the relative distribution pattern provide key evidence to support the use of simulations that can only capture a few seconds of flow data, compared to the hundreds of seconds possible in an experiment. The key role of the lower lateral arm of the wake ring vortex in entraining airborne spray, and the return flow in advecting it to the rear surface is made really clear with this simple system. Of course, we now need to add in wheels and understand the role of the wheel wakes.
Dr Adrian P Gaylard
University of Warwick
Read the Original
This page is a summary of: Simulation of rear surface contamination for a simple bluff body, Journal of Wind Engineering and Industrial Aerodynamics, June 2017, Elsevier,
DOI: 10.1016/j.jweia.2017.02.019.
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