Abstract
Trailing edge-integrated lobed-mixing geometries are proposed as a viable method for road vehicle aerodynamic drag reduction. Experiments are conducted on a 1/24th-scale model, representative of a Heavy Goods Vehicle, at a width-based Reynolds number of 2.8 × 105. A broad range of pitches and penetration angle values is examined, with detailed comparisons also made to high-aspect-ratio rear tapering. Changes to mean drag coefficients and wake velocities are evaluated and assessed from both the time-independent and time-dependent perspectives. Results show significant drag reductions for lower pitches at higher penetration angles, where the performance of regular tapering is found substantially degraded. The mechanisms responsible for drag reduction are identified to be reductions in the wake size and a shift in the vertical wake balance. The former is shown to be a result of the enhancement in inboard momentum close to the trailing edges through the generation of pairs of counter-rotating streamwise vortices, with the latter attributed to the downstream evolution of the vortices. Overall, these results identify such geometries to be suitable for improving vehicle drag while minimising the losses in internal space.
Highlights
Drag reduction of road vehicles remains a key issue at the centre of action against climate change
The best drag reduction of 10.8% is achieved with boat-tail tapers (BTT) a = 15°, in general agreement with van Raemdonck and van Tooren,[7] and Salati et al.[16]
This trend is similar to that observed for the BTT, suggesting some similarities in the drag reduction processes exist between these configurations
Summary
Drag reduction of road vehicles remains a key issue at the centre of action against climate change. Within the UK, the transport sector continues to be the largest contributor to greenhouse gas emissions, constituting 28% of all emissions in 2018.1 Despite accounting for only 5% of total vehicle miles,[2] heavy goods vehicles (HGVs) produce up to 18% of the CO2 emitted by all road transport.[3] At motorway speeds, where these vehicles spend most of their time, as much as 50% of the consumed fuel is spent on overcoming the aerodynamic drag.[4] Understandably, drag reduction concepts are eagerly pursued by many researchers. Aside from having adverse effects on the vehicle’s forward motion, the specific dynamics of the wake often degrade the vehicle’s stability
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More From: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
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