Flows around a deformed pneumatic tyre
Lead Research Organisation:
University of Cambridge
Department Name: Engineering
Abstract
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.
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.
People |
ORCID iD |
| Holger Babinsky (Primary Supervisor) | |
| Alex Parfett (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509620/1 | 01/10/2016 | 30/09/2022 | |||
| 1772086 | Studentship | EP/N509620/1 | 01/10/2016 | 30/09/2020 | Alex Parfett |
| Description | A novel experimental set up has been developed in order to study the flows around a deformed pneumatic tyre. This allows a tyre to be positioned as desired, and dragged through the Cambridge University Engineering Department water towing tank. The tank allows the aerodynamic conditions at the ground, vital for study of flow features in this region, to be simulated more accurately and more cheaply than with a rolling road in a wind tunnel. Using a particle image velocimetry system with newly designed optics, full 3-D velocity flow data has been captured around the tyre for a range of conditions. The experimental set up allows for data to be captured close to the surface of the tyre, ahead, to the side, and behind the contact patch. As such, the formation process of the ground vortices has been observed in detail. A shear layer formed on the front surface of the tyre has been observed to be ejected to the sides, where it rolls up into the primary ground vortex. This is shown to induce separation in the boundary layer on the floor, creating a secondary ground vortex. Significant vorticity has also been observed trapped at the rear of the contact patch, and shown to slowly convect into the ground vortex, contributing to its strength. A novel post processing technique has also been developed which allows the flow field from a single experimental run to be analysed. Previous studies in this area tend to average multiple runs, which reduces noise. Unfortunately, for an unsteady flow such as that behind a tyre, this hides the true instantaneous flow. Using the new technique, a great diversity of flow structures have been observed, revealing the complexity of the flow from moment to moment. In particular, an unsteady process in which each of the two ground vortices generated at the front of the tyre periodically dominate the flow field has been observed. Finally, the tyre has been deformed, by squashing it vertically, cambering to the side and steering (yaw). Cambering to one side has been shown to increase the average strength of the ground vortex on that side, and reduce it on the other. However, using the new post processing technique, it is clear that the instantaneous behaviour still jumps between left and right vortices dominating the flow, but that cambering to one side increases the proportion of the time the vortex on that side dominates for. Vertical squash has a similar effect, with both vorticies increasing in strength. Finally, a yawed tyre is shown to drastically alter the flow field, making it much more stable and gathering most of the front and rear vorticity on one side. This dominance of one vortex persists in time, unlike in the cambered case. |
| Exploitation Route | Some of this data is currently commercially sensitive, with specific applications in developing technology in Formula 1. However, a better understanding of flows around pneumatic tyres stands to improve efficiency of road vehicles through better informed aerodynamic design. This is particularly true in the case of Heavy Goods Vehicles, where underbody drag, heavily influenced by tyre flows, makes up a significant proportion of overall drag. |
| Sectors | Transport |
| URL | https://doi.org/10.17863/CAM.64112 |
| Description | The experimental findings of this project will contribute directly to technical development in the Formula 1 industry. F1 is a significant driver of aerodynamic and automotive technical innovation, with a substantial position in the UK economy, where the vast majority of development takes place. Some of the data from this project is commercially sensitive, however improved understanding of flows around deformed pneumatic tyres also has large implications for the efficiency of road vehicles. Improved understanding of these flows enables designers to improve the efficiency of underbody flows, reducing aerodynamic drag. This is particularly relevant in the case of Heavy Goods Vehicles, where underbody drag forms a large portion of total drag. Such improvements have the potential to significantly reduce transport based emissions, with corresponding social and environmental impact. |
| First Year Of Impact | 2019 |
| Sector | Other |
| Description | Mercedes Collaboration |
| Organisation | Mercedes-Benz Grand Prix Ltd |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | At the Cambridge University Engineering Department, a novel experimental set up was designed to study the flow field around a deformed pneumatic tyre. After further development and manufacture with our partner (see below), an experimental campaign has been conducted, focused on capturing the resulting flow field. Novel post processing tools to analyse this data have been developed and a number of findings have been made (see key findings). |
| Collaborator Contribution | Through this collaboration a novel experimental set up has been developed for the purpose of studying the flow field around a deformed pneumatic tyre. During the latter part of this process, the partner contributed to the design work, and manufactured the majority of the test rig. |
| Impact | A number of findings (see key findings) from the experimental campaign and subsequent analysis stand to contribute to technical development in the F1 industry. Some of this data is currently commercially sensitive, however a better understanding of flows around pneumatic tyres stands to improve efficiency of road vehicles through better informed aerodynamic design. This is particularly true in the case of Heavy Goods Vehicles, where underbody drag, heavily influenced by tyre flows, makes up a significant proportion of overall drag. This collaboration sits solely in the field of experimental aerodynamics. |
| Start Year | 2016 |