Analysis of Wake Pattern for Reducing Aerodynamic Drag of Notchback Model

Nouzawa, Takahide; Haruna, Shigeru; Hiasa, Kazuhiko; Nakamura, Takaki; Satō, Hiroshi

doi:10.4271/900318

Cited by 20 publications

(11 citation statements)

References 6 publications

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“…PIV measurements even further to the left, at y/W = −.33, showed no recirculation and it is postulated that a vortex terminates on the backlight in this region (the left hand UF in Figure 3). This vortex partially resembles the arch vortex proposed by Nouzawa et al [1] except that that work showed the ends of the vortex terminating entirely on the trunk lid on both sides. Figure 3 indicates that it terminates principally on the backlight on the left hand side and the combined observations made here suggest that it terminates at the front of the trunk deck on the right hand side.…”

Section: Flow Field -Time Averagedmentioning

confidence: 69%

“…Figure 1 illustrates the backlight angle (B) and effective backlight angle (B eff ) for a notchback. Nouzawa et al [1] found that the drag coefficient changes with rear end geometry were less extreme for notchbacks than for fastbacks. It should be noted that the effective backlight angle is far from being a perfect index to rear end flow structure, with critical effective backlight angles varying significantly between different notchback geometries (eg: [1] vs [2]).…”

Section: Introductionmentioning

confidence: 99%

“…Nouzawa et al [1] found that the drag coefficient changes with rear end geometry were less extreme for notchbacks than for fastbacks. It should be noted that the effective backlight angle is far from being a perfect index to rear end flow structure, with critical effective backlight angles varying significantly between different notchback geometries (eg: [1] vs [2]). This is further Links between Notchback Geometry, Aerodynamic Drag, Flow Asymmetry and Unsteady Wake Structure illustrated by Howell [3] (summarizing unpublished work by Windsor) which shows that the use of effective backlight angle cannot collapse the drag of different notchback geometries.…”

Section: Introductionmentioning

confidence: 99%

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Links between Notchback Geometry, Aerodynamic Drag, Flow Asymmetry and Unsteady Wake Structure

Sims-Williams¹,

Marwood²,

Sprot³

2011

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

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. (2011) 'Links between notchback geometry, aerodynamic drag, ow asymmetry and unsteady wake structure.', SAE International journal of passenger cars. Mechanical systems., 4 (1). pp. 156-165. Further information on publisher's website:http://dx.doi.org/10.4271/2011-01-0166Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTThe rear end geometry of road vehicles has a significant impact on aerodynamic drag and hence on energy consumption. Notchback (sedan) geometries can produce a particularly complex flow structure which can include substantial flow asymmetry. However, the interrelation between rear end geometry, flow asymmetry and aerodynamic drag has lacked previous published systematic investigation.This work examines notchback flows using a family of 16 parametric idealized models. A range of techniques are employed including surface flow visualization, force measurement, multi-hole probe measurements in the wake, PIV over the backlight and trunk deck and CFD.It is shown that, for the range of notchback geometries investigated here, a simple offset applied to the effective backlight angle can collapse the drag coefficient onto the drag vs backlight angle curve of fastback geometries. This is because even small notch depth angles are important for a sharp-edged body but substantially increasing the notch depth had little further impact on drag.This work shows that asymmetry originates in the region on the backlight and trunk deck and occurs progressively with increasing notch depth, provided that the flow reattaches on the trunk deck and that the effective backlight angle is several degrees below its crucial value for non-reattachment. A tentative mapping of the flow structures to be expected for different geometries is presented.CFD made it possible to identify a link between flow asymmetry and unsteadiness. Unsteadiness levels and principal frequencies in the wake were found to be similar to those for high-drag fastback geometries. The shedding of unsteady transverse vortices from the backlight recirculation region has been observed.

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Section: Flow Field -Time Averagedmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Links between Notchback Geometry, Aerodynamic Drag, Flow Asymmetry and Unsteady Wake Structure

Sims-Williams¹,

Marwood²,

Sprot³

2011

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

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“…Figure 8 shows the iso-surfaces of the mean static pressure normalized by the inlet dynamic pressure. The most famous and dominant wake structure of the notchback-type vehicle is the pair of trailing vortex emanating from the rear pillars (e.g., Nouzawa et al [16]). It is interesting to note that other vortices generated by the front pillars, the door mirrors, the front tire house, and possibly the underbody vortices mingle together at the rear end of the vehicle and contribute to form the trailing vortices.…”

Section: Vortex Structures Around the Vehiclementioning

confidence: 99%

Computational visualization of unsteady flow around vehicles using high performance computing

et al. 2009

Self Cite

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One of the largest-scale unstructured Large Eddy Simulation (LES) of flow around a full-scale road vehicle is conducted on the Earth Simulator in Japan. The main objective of our study is to look into the validity of LES for the assessment of vehicle aerodynamics, especially in the context of its possibility for unsteady or transient aerodynamic forces. Firstly, the aerodynamic LES proposed is quantitatively validated on the ASMO simplified model by comparing the mean pressure distributions on the vehicle surface with those obtained by a conventional Reynolds-Averaged Navier-Stokes simulation (RANS) or a wind tunnel measurement. Then, the method is applied to the full-scale vehicle with complicated geometry to qualitatively investigate the capability of capturing organized flow structures around the vehicle. Finally, unsteady aerodynamic forces acting on the vehicle in transient yawing-angle change are estimated and relationship between the flow structures and the transient aerodynamic forces is mentioned. As a result, it is demonstrated that LES will be a powerful tool for the vehicle aerodynamic assessment in the foreseeable future, because it can provide precious aerodynamic data which conventional wind tunnel tests or RANS simulations are difficult to provide.

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“…Looking into the literature shows that many notchback like geometry studies were done on simplified shapes and generic bodies [2,3,5,9,10,11,12]. These investigations show that the flow field is different, as for instance vortices are different in size and position, but on the other hand main features like saddle points and foci are present in a similar way for the different geometries.…”

Section: Introductionmentioning

confidence: 99%

Investigations of the Rear-End Flow Structures on a Sedan Car

Kounenis

Bonitz

Ljungskog

et al. 2016

SAE Technical Paper Series

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractThe aerodynamic drag, fuel consumption and hence CO 2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle.This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60.First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities. The flow field away from the surface is then analysed using PIV measurements and CFD for the scale model and CFD simulations for the full scale vehicle. The flow field is investigated regarding its singular points in cross-planes and the correlation between the patterns for the two geometries is analysed.Furthermore, it is discussed how the occurring structures can be described in more generalized terms to be able to compare different vehicle geometries regarding their flow field properties.The results show the extent to which detailed flow structures on similar but distinct vehicles are comparable; as well as providing insight into the complex 3D wake flow.

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Analysis of Wake Pattern for Reducing Aerodynamic Drag of Notchback Model

Cited by 20 publications

References 6 publications

Links between Notchback Geometry, Aerodynamic Drag, Flow Asymmetry and Unsteady Wake Structure

Links between Notchback Geometry, Aerodynamic Drag, Flow Asymmetry and Unsteady Wake Structure

Computational visualization of unsteady flow around vehicles using high performance computing

Investigations of the Rear-End Flow Structures on a Sedan Car

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