Flows around a deformed pneumatic tyre

At motorway speeds, aerodynamic drag represents the largest resistive force to a vehicle, and
therefore has the greatest impact on fuel efficiency. The reduction of the aerodynamic drag of
road vehicles has the potential to significantly reduce fossil fuel use and emission of pollutants,
and is of interest to the automotive industry for both environmental and economic reasons. A
significant proportion of the drag from such vehicles, particularly in the case of HGVs, is due
to the underbody. The flow in this region is highly influenced by the flow around the tyres. An
understanding of this flow is therefore crucial during the design process when attempting to
reduce aerodynamic drag on a vehicle.
This project aims to characterise the flow around a deformed pneumatic tyre. During
conventional use, particularly when breaking, accelerating, and cornering, a tyre experiences
significant variation in its loading, deforming its shape in a variety of ways. Although flows
around a tyre have been well documented in the literature, very few studies have attempted
to understand how the flow field changes when a tyre is exposed to varying loading conditions.
One of the greatest influences on the underbody flow field from the tyre comes from two large
ground vortices, which are generated at the interface between the road and the tyre. This
project aims to understand how the formation of these vortices is influenced by the deformation
of the tyre near the ground, and what effect this has on the resulting path and strength of such
vortices.
Correct replication of the formation of ground vortices about a wheel is highly dependent on
an accurate replication of the conditions at the ground. Typically, this would be achieved in a
wind tunnel using a rolling road, with boundary layer suction. This is both highly expensive
and often error prone. Further, the deformed tyre presents a significant challenge to simulate
accurately due to the small angles the tyre forms with the road. This research will be carried
out experimentally in a water towing tank, which is a novel method for studying tyre
aerodynamics. It represents a much lower cost and higher accuracy method for replicating
ground conditions. The use of water also facilitates the use of a high speed stereoscopic
Particle Image Velocimetry (PIV) system, which will be used to capture detailed three
dimensional flow field data around the tyre. In particular, PIV can non-invasively develop
detailed flow fields in the crucial regions near the ground where the ground vortices are
formed, giving more information to vehicle designers trying to mitigate their effects.
This project comes within the Fluid Dynamics and Aerodynamics EPSRC research area.