Abstract
A new method for supporting ground vehicle wind tunnel models is proposed. The technique employs a centrally mounted sting connecting the front face of the vehicle, adjacent to the floor, to a fixed point further upstream. Experiments were conducted on a 1/24th-scale model, representative of a Heavy Goods Vehicle, at a width-based Reynolds number of 2.3 × 105, with detailed comparisons made to more established support methodologies. Changes to mean drag coefficients, base pressures and wake velocities are all evaluated and assessed from both time-independent and time-dependent perspectives, with a particular focus within the wake region. Results show subtle changes in drag coefficient, together with discrete modifications to the flow-field, dependent on the method adopted. Subtle differences in base pressures and wake formation are also identified, with mounting the model upstream found to demonstrate retention of many of the beneficial effects of other techniques without suffering their deficiencies. Overall, these results identify the upstream mounting methodology as a viable alternative to currently available and more well-established techniques used to facilitate wind tunnel aerodynamic interrogation.
Highlights
Wind tunnel testing is a key tool used in road vehicle aerodynamic design to both assess and improve critical performance metrics
This baseline, representative of a Heavy Goods Vehicle (HGV), includes a rounded front profile based on the Ground Transportation System (GTS)[28] and neglects fine detail
The significance of the tractor-trailer gap at reducing trailer drag is highlighted, with calculated trailer base drag (CDTb) contributing between 13.6% and 14.8% of total model drag (CDM)
Summary
Wind tunnel testing is a key tool used in road vehicle aerodynamic design to both assess and improve critical performance metrics. While the main aim of these structures is to hold the model, their presence often acts to increase measurement uncertainty in ways that remain difficult to quantify and challenging to predict.[2,3,4,5,6] Among the most common effects are changes to the surrounding flow-field, such as those occurring at the support-model junction.[3] Simpson[7] studied such junction flows between planar surfaces and streamlined obstructions, and showed the stagnation at the obstruction’s leading edge to provoke the upstream surface boundary layer to separate, resulting in the generation of horseshoe vortices, which propagate downstream These vortices are typically small, less than the boundary layer thickness, and their strength increases with the bluntness of the obstacle.[7] A secondary separation may occur at the obstacle’s trailing edge, with Hetherington,[3] who investigated similar effects on various mounting configurations, noting a significant localised momentum wake deficit caused by the support.
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