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The aerodynamic characteristics of automobile wheels - CFD prediction and wind tunnel experiment

by Axon, Lee

Abstract (Summary)
When analyzing the aerodynamic characteristics of a road vehicle, the flow around

the basic body shape is complicated by the presence of the rotating wheels. Even

though on most vehicles the wheels are partially shrouded their effect on the flowfield

is still considerable. Despite this, very little is understood about the flow around

a rotating wheel. This thesis describes the development of a validated steady state

Reynolds Averaged Navier-Stokes CFD model to investigate the flow around automobile

wheels.

As all the previous investigations into the aerodynamic characteristics of wheel flows

had been experimental, preliminary computational studies were performed. The

basis of these was the 2D circular cylinder. The effects of cylinder rotation and

ground proximity were modelled, and strategies for boundary conditions and mesh

topology were developed.

This work was extended into 3D with the modelling of an isolated wheel, both rotating

and stationary. Using existing experimental data for validation, an extensive

investigation into the effects of solver numerics, symmetry planes, turbulence models,

and the method of turbulent closure was performed. An optimum solver configuration

was developed which comprised of the RNG k-E turbulence model with full

boundary layer closure. It was accurately predicted that the rotating wheel generates

less lift and drag than the equivalent stationary wheel. A number of postulated

experimental flow features were captured in the final solutions.

Using a parallel experimental study to provide further validation data, the CFD

model was extended to incorporate an asymmetric shroud containing a wheelhouse

cavity. The influence of the rotation of the wheel, the geometry of the shroud,

and the thickness of the stationary groundplane boundary layer were investigated.

The rotating wheel now produced more drag than the equivalent stationary wheel.

Reductions in wheel drag were found with a reduction in the ride height of the

shroud, and with the addition of spoilers to the lower front edge of the shroud.

Increasing the stationary groundplane boundary layer thickness also reduced the

wheel drag. The effects of these changes on the wheel surface pressure distributions

are presented.

Bibliographical Information:

Advisor:Garry, Kevin P. (supervisor)

School:Cranfield University

School Location:United Kingdom

Source Type:Master's Thesis

Keywords:

ISBN:

Date of Publication:09/01/1999

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