Topology of Flow Separation on Three-Dimensional Bodies

Chapman, G. T.; Yates, Leslie A.

doi:10.1115/1.3119507

Cited by 71 publications

(43 citation statements)

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“…This reattachment is due to the spanwise motion and not to the separated streamlines reaching the wall. The nearbed streamlines resemble those of Allen (1968), and the bulging effect is explained by the saddle point of separation caused by the 3D separation at the sinusoidal crestlines (Chapman & Yates 1991). The average value of the reattachment length is lower for 3D cases than the corresponding 2D case due to the effect of the streamwise vortices, which are correlated with the amplitude of the crestline.…”

Section: Discussionsupporting

confidence: 53%

“…This secondary flow near the bed results in the saddle point of separation over the lobe plane (point C in Figure 3(a), and points S s in Figure 4) and inhibits the reattachment of the separated flow over the lobe. Symmetric 3D separation lines result in "Type I" separation with symmetry breaking discussed by Chapman & Yates (1991), in which a saddle point of separation (S Figure 4) downstream of N s in the symmetry plane (the lobe plane). We will show that the S 2 s points over the lobe plane cause the deformation of the reattachment line (based on our definition), known as "bulging".…”

Section: Problem Formulationmentioning

confidence: 99%

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Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

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This is the accepted version of the paper.This version of the publication may differ from the final published version. We performed large-eddy simulations of flow over a series of three-dimensional dunes at laboratory scale (Reynolds number based on the average channel depth and streamwise velocity was 18,900) using the Lagrangian dynamic eddy-viscosity subgrid-scale model. The bedform three-dimensionality was imposed by shifting a standard two-dimensional dune shape in the streamwise direction according to a sine wave. The statistics of the flow are discussed in ten cases with in-phase and staggered crestlines, different deformation amplitudes and wavelengths. The results are validated qualitatively against experiments. The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which in turn may cause secondary flow across the stream, which directs lowmomentum fluid, near the bed, toward the lobe (the most downstream point on the crestline) and high-momentum fluid, near the top surface, toward the saddle (the most upstream point on the crestline). The mean flow is characterized by a pair of counterrotating streamwise vortices, with core radius of the order of the flow depth. However, for wavelengths smaller than the flow depth, the secondary flow exists only near the bed and the mean flow away from the bed resembles the two-dimensional case. Staggering the crestlines alters the secondary motion; the fastest flow occurs between the lobe and the saddle planes, and two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The distribution of the wall stress and the focal points of separation and attachment on the bed are discussed. The sensitivity of the average reattachment length, depends on the induced secondary flow, the streamwise and spanwise components of the channel resistance (the skin friction and the form drag), and the contribution of the form drag to the total resistance are also studied. Three-dimensionality of the bed increases the drag in the channel; the form drag contributes more than in the two-dimensional case to the resistance, except for the staggered-crest case. Turbulent-kinetic energy is increased in the separated-shear layer by the introduction of three-dimensionality, but its value normalized by the plane-averaged wall stress is lower than in the corresponding twodimensional dunes. The upward flow on the stoss side and higher deceleration of flow on the lee side over the lobe plane lift and broaden the separated-shear layer, respectively, affecting the turbulent kinetic energy. Permanent repository link

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Section: Discussionsupporting

confidence: 53%

Section: Problem Formulationmentioning

confidence: 99%

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

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“…This discrepancy is only apparent. As discussed by Perry and Hornung (1984) and Chapman and Yates (1991), many of the surface topological features arise due to vortex interactions in the immediate vicinity of the wall and, when the velocity field is measured above the interaction plane, the saddle-node-saddle will merge to appear as a single saddle point, but the Poincare-Bendixon index remains unchanged and the flow field is still topologically consistent. Fig.…”

Section: Positive Bifurcation Linementioning

confidence: 90%

Vortical structures around a surface-mounted pyramid in a thin boundary layer

AbuOmar

Martinuzzi

2008

Journal of Wind Engineering and Industrial Aerodynamics

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“…One possibility for a more generic flow field description could be the investigation of singular points [17]. This method was already used in some publications, for instance in [4, 5, 6, 7, 8 17, 18].…”

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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Topology of Flow Separation on Three-Dimensional Bodies

Cited by 71 publications

References 0 publications

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Vortical structures around a surface-mounted pyramid in a thin boundary layer

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

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