Investigation of Passive Porosity as a Means for Bluff-Body Drag Reduction

Gatto, A.; Babinsky, Holger

doi:10.4271/02-11-01-0006

Cited by 2 publications

References 10 publications

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Experimental study on drag reduction of the turbulent boundary layer via porous media under nonzero pressure gradient

Zhang

et al. 2022

Physics of Fluids

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The complex surface of an aircraft generates a nonzero pressure gradient flow. In this study, the boundary conditions of favorable and adverse pressure gradients are constructed in a small low-turbulence wind tunnel test section. Hot-wire anemometers and time-resolved image velocimetry are used to analyze the flow structure in a fully developed turbulent boundary layer with porous media. The effects of the porous surface on the statistical characteristics of the turbulent flow field and turbulent flow structure are analyzed and discussed. The results show that porous media reduce the velocity gradient in the linear layer, and the friction drag reduction effect is higher downstream of the porous wall. The drag reduction effect decreases along the flow direction. A wall with a 10 pores per inch produces a slightly better drag reduction effect than smooth wall. The maximum local drag reduction effect of a 10-pores-per-inch porous wall is 43.7% under a favorable pressure gradient and 42.3% under an adverse pressure gradient. The velocity streaks in the inner layer show that the porous wall widens the low-velocity streaks, making them more stable, while the high-speed streaks decrease in size under the pressure gradient. In the case of the adverse pressure gradient, the structure of the streaks becomes blurred, and their strength weakens. Under both favorable and adverse pressure gradients, the porous media lift up the coherent structures near the wall, thus weakening the large-scale coherent wall structures.

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Experimental study on drag reduction of the turbulent boundary layer via porous media under nonzero pressure gradient

Zhang

et al. 2022

Physics of Fluids

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The Effect of Cross-Flow Vortex Trap Devices on the Aerodynamic Drag of Road Haulage Vehicles

Story¹,

Garcia²,

Babinsky³

2021

SAE Technical Paper Series

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The effect of Cross-Flow Vortex Trap Devices (CVTDs) on the local flowfield and vehicle drag at a range of yaw angles has been investigated in wind tunnel experiments. The CVTD is a flow control device proposed by Bauer and Wood that aims to reduce the sensitivity of articulated road haulage vehicles to crosswinds by managing the tractortrailer gap cross-flow. A 1/10 th scale model is used in a low speed wind tunnel at a Reynolds number of 900,000. The aerodynamic drag force is measured using a load cell connected to a rotating, raised ground plane. This research also uses tuft flow visualisation to examine the local flowfields, and pressure taps to determine trailer pressure distributions. It is found that a configuration of four 45% length CVTDs reduces the wind-averaged drag coefficient by 12%. The drag mechanisms that are responsible for the reduced drag include a lower average pressure on the trailer front face, a removal of the separation on the leeward side of the trailer due to a reduction in gap cross-flow, and an increase in pressure on the leeward side of the trailer behind the tractor-trailer gap. Furthermore, it is found that the drag reduction performance increases with CVTD length but does not vary with the number of CVTDs between one and four. These results suggest that using a single CVTD or flexible sheet of material at the centreline of the cab-gap is the most viable solution, as there is no further benefit to using multiple devices. In addition, it allows for the greatest CVTD length without impeding articulation.

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Investigation of Passive Porosity as a Means for Bluff-Body Drag Reduction

Cited by 2 publications

References 10 publications

Experimental study on drag reduction of the turbulent boundary layer via porous media under nonzero pressure gradient

Experimental study on drag reduction of the turbulent boundary layer via porous media under nonzero pressure gradient

The Effect of Cross-Flow Vortex Trap Devices on the Aerodynamic Drag of Road Haulage Vehicles

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