Asymmetry and global instability of real minivans' wake

Bonnavion, Guillaume; Cadot, Olivier; Herbert, Vincent; Parpais, S.; Vigneron, Rémi; Délery, Jean

doi:10.1016/j.jweia.2018.11.006

Cited by 29 publications

(19 citation statements)

References 18 publications

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“…The recent observations of turbulent wake dynamics from rectangular base bluff bodies report on the switching dynamics between two very distinctive global states of the wake [5,6]. Each wake state is breaking the symmetry on timescales much longer than the convective timescale as illustrated in Figure 1.…”

Section: Introductionmentioning

confidence: 98%

“…The research paper we present is not exploiting an analogy as in these cited works, but we wished to introduce our original contribution by mentioning a possible analogy as a tribute to Yves. [5,6] about the turbulent wake of a squareback body at Re ∼ 10 5 showing the instantaneous streamwise velocity field with a laterally deflected wake on the right hand-side (a) and the motion of the deflected position with corresponding statistics (b). Schematic drawing of the two wake states denoted P and N with their associated base pressure gradient (c).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry

Cadot¹,

Almarzooqi²,

Legeai³

et al. 2020

Comptes Rendus. Mécanique

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry

Cadot¹,

Almarzooqi²,

Legeai³

et al. 2020

Comptes Rendus. Mécanique

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“…drag, should act on the front separation bubbles. These results also may indicate that streamlined squareback bluff-bodies, such as the Renault Kangoo in the study by Bonnavion et al [37] or the Citroën Berlingo in the study by Bonnavion et al [38], might first present wake bimodality once the vehicle is yawed and/or pitched because only in these conditions do prominent separation bubbles manifest themselves at the vehicle's front.…”

Section: Appendixmentioning

confidence: 82%

Simulation of wake bimodality behind squareback bluff-bodies using LES

Hesse

Morgans

2021

Preprint

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A large eddy simulation (LES) study of the flow around a 1/4 scale squareback Ahmed body at Re H = 33, 333 is presented. The study consists of both wall-resolved (WRLES) and wall-modelled (WMLES) simulations, and investigates the bimodal switching of the wake between different horizontal positions. Within a non-dimensional time-window of 1050 convective flow units, both WR-LES and WMLES simulations, for which only the near-wall region of the turbulent boundary layer is treated in a Reynolds-averaged sense, are able to capture horizontal (spanwise) shifts in the wake's cross-stream orientation. Equilibrium wall-models in the form of Spalding's law and the log-law of the wall are successfully used. Once these wall-models are, however, applied to a very coarse nearwall WMLES mesh, in which a portion of the turbulent boundary layer's outer region dynamics is treated in a Reynolds-averaged manner as well, large-scale horizontal shifts in the wake's orientation are no longer detected. This suggests larger-scale flow structures found within the turbulent boundary layer's outer domain are responsible for generating the critical amount of flow intermittency needed to trigger a bimodal switching event. By looking at mean flow structures, instantaneous flow features and their associated turbulent kinetic energy (TKE) production, it becomes clear that the front separation bubbles just aft of the Ahmed body nose generate high levels of TKE through the shedding of large hairpin vortices. Only in the reference WRLES and (relatively) fine near-wall

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“…The square-back and cavity geometries were investigated for lateral and vertical symmetry breaking modes as this has previously been reported in the literature for similar models (Volpe et al 2015;Bonnavion and Cadot 2018;Barros et al 2016;Bonnavion et al 2019;Perry et al 2016;Grandemange et al 2013;Li et al 2016) and is linked to the vehicle drag. The probability density function for a laterally located pressure tap as well as the vertical pressure gradient showed no signs of switching between symmetry breaking modes for any of the geometries.…”

Section: • -Yawmentioning

confidence: 99%

“…Applying a cavity to the base of the geometry, by extending the perimeter, is effective at 0 • yaw (Evrard et al 2016;Duell and George 1993;Bonnavion et al 2019;Lucas et al 2017), with as much as 11% reduction in drag Duell and George (1993). Cavities are often tapered to reduce the wake size and further increase the drag reduction.…”

Section: Introductionmentioning

confidence: 99%

Drag reduction mechanisms on a generic square-back vehicle using an optimised yaw-insensitive base cavity

et al. 2021

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Regulations on global greenhouse gas emission are driving the development of more energy-efficient passenger vehicles. One of the key factors influencing energy consumption is the aerodynamic drag where a large portion of the drag is associated with the base wake. Environmental conditions such as wind can increase the drag associated with the separated base flow. This paper investigates an optimised yaw-insensitive base cavity on a square-back vehicle in steady crosswind. The test object is a simplified model scale bluff body, the Windsor geometry, with wheels. The model is tested experimentally with a straight cavity and a tapered cavity. The taper angles have been optimised numerically to improve the robustness to side wind in relation to drag. Base pressures and tomographic Particle Image Velocimetry of the full wake were measured in the wind tunnel. The results indicate that a cavity decreases the crossflow within the wake, increasing base pressure, therefore lowering drag. The additional optimised cavity tapering further reduces crossflow and results in a smaller wake with less losses. The overall wake unsteadiness is reduced by the cavity by minimising mixing in the shear layers as well as dampening wake motion. However, the coherent wake motions, indicative of a balanced wake, are increased by the investigated cavities. Graphical abstract

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Asymmetry and global instability of real minivans' wake

Cited by 29 publications

References 18 publications

On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry

On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry

Simulation of wake bimodality behind squareback bluff-bodies using LES

Drag reduction mechanisms on a generic square-back vehicle using an optimised yaw-insensitive base cavity

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