Effect of ventilation on the flowfield around a sphere

Suryanarayana, GK; Meier, G. E. A.

doi:10.1007/bf00193853

Cited by 34 publications

(21 citation statements)

References 14 publications

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“…18 The effects of free stream turbulence intensity, sphere surface roughness, and supporting system rigidity have been suggested as possible reasons for this disagreement. 5,19 Our numerical results qualitatively reproduce the drag phenomenon and are in good agreement with those of Wieselsberger. Since there was no turbulence intensity in the free stream in our numerical simulation, our results did not clarify the effects of turbulence intensity on the critical Reynolds number and on the turbulent transition in the separated and reattached surface boundary layer.…”

Section: -3supporting

confidence: 79%

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

2012

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Maximum entropy states of quasi-geostrophic point vortices Phys. Fluids 24, 056601 (2012) Effect of swirl decay on vortex breakdown in a confined steady axisymmetric flow Phys. Fluids 24, 043601 (2012) Simulations of turbulent rotating flows using a subfilter scale stress model derived from the partially integrated transport modeling method Phys. . The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.

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Section: -3supporting

confidence: 79%

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

2012

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“…Their results could enhance understanding of the vortical flow structure and shear-layer instability inside the near-wake of a sphere [3]. It is well-known that in uncontrolled flows around a sphere, the drag coefficients rapidly decrease down to approximately 0.07 and this phenomenon is called the drag crisis occurred around Re!2x10 5 [4] (Achenbach, 1972). The cause of this rapid drag-coefficient reduction is the existence of small separation bubble(s) above the surface.…”

Section: Introductionmentioning

confidence: 96%

“…The cause of this rapid drag-coefficient reduction is the existence of small separation bubble(s) above the surface. Suryanarayana and Meier (1995) and Suryanarayana & Prabhu (2000) investigated the ventilation effects on the flow characteristics in the wake of a sphere [5][6]. They recorded that the ventilation decreases the drag coefficient for Reynolds number higher than critical value while it is less effect on the flow structure at intermediate Reynolds numbers.…”

Section: Introductionmentioning

confidence: 99%

Turbulent shear flow downstream of a sphere with and without an o-ring located over a plane boundary

Özgören

Okbaz

Doğan

et al. 2012

EPJ Web of Conferences

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“…The ventilation resulted in a ring shaped stagnation at the front of sphere and a toroidal recirculating region, due to an additional shear layer, at the base of the model. Suryanarayana [18] went on to show that by introducing the ventilation, and integrating the pressures over the sphere, that the pressure drag nearly becomes zero at supercritical Reynolds numbers.…”

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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Effect of ventilation on the flowfield around a sphere

Cited by 34 publications

References 14 publications

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

Turbulent shear flow downstream of a sphere with and without an o-ring located over a plane boundary

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

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