The Impact of Underbody Roughness on Rear Wake Structure of a Squareback Vehicle

Perry, Anna-Kristina; Passmore, Martin A.

doi:10.4271/2013-01-0463

Cited by 10 publications

(8 citation statements)

References 22 publications

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“…The location of these perturbations varies from upstream of the base of the geometry (inflow conditions (Kang et al 2021), asymmetric boat-tailing/tapering (Bonnavion & Cadot 2019;Pavia, Passmore & Varney 2019), yaw (Cadot, Evrard & Pastur 2015;Li et al 2019) or pitch (Bonnavion & Cadot 2018)) to the base of the geometry (pulsed jets (Li et al 2016), active flaps (Brackston et al 2016)). An important subset of asymmetric perturbations is located between the underside and the ground, for example ground clearance (Grandemange, Gohlke & Cadot 2013a), the ratio of the underbody velocity to free-stream velocity (Castelain et al 2018) and underbody roughness (Perry & Passmore 2013). The importance of this subset lies in their frequent encounters under real road conditions.…”

Section: Introductionmentioning

confidence: 99%

Near wake interactions and drag increase regimes for a square-back bluff body

et al. 2022

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The three-dimensional near wake of a square-back bluff body in ground proximity is experimentally perturbed by placing a pair of D-shaped obstacles under the body. Five obstacle widths $d$ , from 12 % to 26 % of the height of the body, are used to perform a sensitivity study of the body's pressure drag by varying the relative distance $l$ between the obstacle pair and the base. Two successive drag-sensitive regimes are identified for obstacle-to-base distances $l/d < 2.5$ , where the pressure drag of the body is increased up to 22 %. In different regimes, the flow dynamics measured downstream of the obstacles are found to be very different. When the obstacles are the closest to the base, $l/d<1.5$ , the pressure drag changes of the main body are driven by mean merging between the wakes of the obstacles and of the main body, and scale with $d$ . Contrarily, when the obstacles are located farther from the base, $1.5< l/d<2.5$ , the wakes of the obstacles are isolated from the main body wake. Here the dynamics of the obstacle wake drive the pressure drag changes of the main body, which scale with $d^{2}$ . In both regimes, we measure a mean mass transfer from the wake of the main body to the wakes of the obstacles. This is the main mechanism responsible for the pressure drag changes. Using our results and reference studies describing the effects of base suction on the pressure drag of bluff bodies, a physical model is proposed to explain the contrasting scalings of the pressure drag increase in the different regimes observed in this study.

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Section: Introductionmentioning

confidence: 99%

Near wake interactions and drag increase regimes for a square-back bluff body

et al. 2022

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“…Typical passive methods such as side tapering [4,5], roof tapering [4,6,7,8,9], roughness strips [10] and underbody tapering [11,12] have all been shown to result in base drag reductions. Active methods have also been tested with drag reductions being reported but little shown in terms of net energy reduction (as the systems require energy input); these include rolling trailing and leading edges [13], blowing [14] and thermal riblets [15].…”

Section: Introductionmentioning

confidence: 99%

The Effect of Passive Base Ventilation on the Aerodynamic Drag of a Generic SUV Vehicle

Varney¹,

Passmore²,

Gaylard³

2017

SAE Int. J. Passeng. Cars - Mech. Syst.

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INTRODUCTIONAerodynamic drag is an increasing concern for vehicle manufacturers due to its impact on CO 2 emissions and fuel economy. For instance, the European Union will phase in significant penalties for CO 2 emissions above a mass-dependent limit curve from 2020 [1]. As Sport Utility Vehicles (SUVs) are the most popular body type [2], the methods of reducing their drag come under closer scrutiny, specifically when the success of these vehicles owes much to elements of design and utility.The blunt nature of SUV rear geometries arises from their historical use as working vehicles, with a need for maximal access to a large rear load space, whilst maintaining off-road capability. For squareback geometries, such as these, more than one-third of the aerodynamic drag is attributable to the rear surfaces [3], resulting from separation at the trailing edges leading to low pressure on the base.In order to combat the depressed static pressure on the base of vehicles a number of studies have been done to investigate base pressure recovery. Typical passive methods such as side tapering [4,5], roof tapering [4,6,7,8,9], roughness strips [10] and underbody tapering [11,12] have all been shown to result in base drag reductions.Active methods have also been tested with drag reductions being reported but little shown in terms of net energy reduction (as the systems require energy input); these include rolling trailing and leading edges [13], blowing [14] and thermal riblets [15].Both passive and active methods alter the shear layers bounding the wake of the vehicle and, as a result change the base pressure and reduce drag. Typically the reduction in drag is shown to be due to the increase in base pressure [4,5,7,8] Adrian Gaylard Jaguar Land Rover ABSTRACT Sports Utility Vehicles (SUVs) typically have a blunt rear end shape (for design and practicality), however this is not beneficial for aerodynamic drag. Drag can be reduced by a number of passive and active methods such as tapering and blowing into the base. In an effort to combine these effects and to reduce the drag of a visually square geometry slots have been introduced in the upper side and roof trailing edges of a squareback geometry, to take air from the freestream and passively injects it into the base of the vehicle to effectively create a tapered body.This investigation has been conducted in the Loughborough University's Large Wind Tunnel with the ¼ scale generic SUV model. The basic aerodynamic effect of a range of body tapers and straight slots have been assessed for 0° yaw. This includes force and pressure measurements for most configurations. The slots generate useful, but small, drag reductions with the best configurations giving reductions in drag coefficient (C d ) of approximately 0.01, whereas the best taper configurations reduce C d by close to 0.035. The slots also have a tendency to modify the lift.

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“…It is widely accepted that changing the size and shape of this wake structure can increase the base pressure and thereby reduce the pressure drag. Many previous studies have demonstrated the effects of passive elements such as splitter plates and base cavities (Duell and George 1993), passive base bleed (Brown et al 2010), base slats (Littlewood et al 2011), forebody roughness (Van Raemdonck and Van Tooren 2008), underbody roughness (Perry and Passmore 2013) and base flaps (Grandemange et al 2013c). Research has also been conducted into several active flow control techniques such as suction (Rouméas et al 2009b), blowing (Littlewood and Passmore 2012), oscillated suction and blowing (Kim et al 2004) and moveable vortex…”

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confidence: 99%

Influence of short rear end tapers on the wake of a simplified square-back vehicle: wake topology and rear drag

2016

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As vehicle manufacturers work to reduce energy consumption of all types of vehicles, external vehicle aerodynamics has become increasingly important. Whilst production vehicle shape optimisation methods are well developed, the need to make further advances requires deeper understanding of the highly three-dimensional flow around bluff bodies. In this paper, the wake flow of a generic bluff body, the Windsor body, based on a square-back car geometry, was investigated by means of balance measurements, surface pressure measurements and 2D particle image velocimetry planes. Changes in the wake topology are triggered by the application of short tapers (4 % of the model length) to the top and bottom edges of the base, representing a shape optimisation that is realistic for many modern production vehicles. The base drag is calculated and correlated with the aerodynamic drag data. The results not only show the effectiveness of such small devices in modifying the time average topology of the wake but also shed some light on the effects produced by different levels of upwash and downwash on the bi-stable nature of the wake itself.

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The Impact of Underbody Roughness on Rear Wake Structure of a Squareback Vehicle

Cited by 10 publications

References 22 publications

Near wake interactions and drag increase regimes for a square-back bluff body

Near wake interactions and drag increase regimes for a square-back bluff body

The Effect of Passive Base Ventilation on the Aerodynamic Drag of a Generic SUV Vehicle

Influence of short rear end tapers on the wake of a simplified square-back vehicle: wake topology and rear drag

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