Abstract
The aim of this research was to improve the understanding of the complex flow features found around a wheel and wheelhouse and to examine how the lateral displacement of the wheel affects these features and the production of exhibited pressures and forces. A bespoke rotating wheel rig and accompanying wheelhouse with a fully-pressure-tapped wheel arch was designed and manufactured at Loughborough University. Wind tunnel tests were performed where force and pressure measurements and Particle Image Velocimetry (PIV) data were obtained. The experimental data was used to validate unsteady CFD predictions where a k- ω SST Improved Delayed Detached Eddy Simulation (IDDES) turbulence model was used in STAR-CCM+ (10.04.009, Siemens). The CFD showed good agreement with all trends of the experimental results providing a validated numerical methodology. For both methodologies, a lower amount of wheelhouse drag was found generated when the wheel was rotating. However, the CFD showed that whilst this was the case, total configuration drag had increased. This was attributed to an increase of the wheel and axle drag, illustrated by the change in separation over the wheel itself when located within a wheelhouse and so overcompensating the reduction in body and stand drag. Differences in vortex locations when comparing to previously-attained results were due to differences in housing geometry, such as blockage in the cavity or housing dimensions. Experimental and computational results showed that up until a 10 mm displacement outboard of the housing, overall drag decreased. The reduction in housing drag was credited to a reduction in the size of outboard longitudinal vortex structures. This led to the lateral width of the shear layer across the housing side being narrower. Overall, this study identified that there were potential benefits to be gained when offsetting a wheel outboard of the longitudinal edge of a model housing.
Highlights
This study utilised a 60%-scale isolated wheel model, the details of which can be found in Rajaratnam and Walker [10], in tandem with a representative, quarter car wheelhouse structure; see
The model scaling considerations were set based on tests previously conducted by Cogotti [9] and confirmed by Rajaratnam and Walker [10], where the trend line found from the pre-post critical Reynolds number, for a stationary isolated wheel configuration, illustrated a transition from pre-post critical drag
The majority of the wheelhouse structure was made from wire-cut panels of craft foam, which were fixed onto an aluminium extrude internal frame
Summary
For the majority, concentrated on minimising the drag created by the rear end of vehicles, as this can account for up to 70% of the total vehicle drag, as found from a simplified model by Ahmed et al [2]. Fewer publications have focused on wheel and wheelhouse flows these have been shown to contribute between 20% and 40% of a passenger vehicle’s overall drag and strongly influence the rear-end drag, as stated by Hucho [3], Wickern et al [4] and Elofsson and Bannister [5]. The importance of rotation and ground contact on the pressure and velocity distribution over the wheel has been well defined, as shown by Morelli [6], Stapleford and Carr [8], Cogotti [9] and Rajaratnam and Walker [10]. The inclusion of wheels on vehicles located within housings adds a significant amount of complexity to the aerodynamic behaviour of wheels due to the interaction of vortex shedding, swirling motion and strong pressure gradients within the cavity [11]
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