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Technical Briefs

Flow Bistability Downstream of Three-Dimensional Double Backward Facing Steps at Zero-Degree Sideslip

[+] Author and Article Information
Benjamin B. Herry1

 ONERA, Applied Aerodynamics Department, MMHD unit, 5 boulevard Paul Painlevé, FR-59045, Lille Cedex, Francebenjamin.herry@onera.fr

Laurent Keirsbulck

 TEMPO-Université de Valenciennes, Le Mont Houy, 59313 Valenciennes Cedex 9, Francelaurent.keirsbulck@univ-valenciennes.fr

Larbi Labraga

 TEMPO-Université de Valenciennes, Le Mont Houy, 59313 Valenciennes Cedex 9, Francelarbi.labraga@univ-valenciennes.fr

Jean-Bernard Paquet

 ONERA, Applied Aerodynamics Department, MMHD unit, 5 boulevard Paul Painlevé, FR-59045, Lille Cedex, Francejean-bernard.paquet@onera.fr

1

Corresponding author.

J. Fluids Eng 133(5), 054501 (Jun 07, 2011) (4 pages) doi:10.1115/1.4004037 History: Received July 12, 2010; Revised April 14, 2011; Published June 07, 2011; Online June 07, 2011

The flow downstream of a three-dimensional double backward facing step (3D DBWFS) is investigated for Reynolds number Reh ranging from 5×103 to8×104 (based on the first step height h). The flow is studied both qualitatively by means of laser tomoscopy and oil-flow visualizations and quantitatively by means of particle image velocimetry (PIV) measurements. In particular, the results show a mean flow asymmetry. A sensitivity study around zero degree sideslip has shown that the flow is bistable for this geometry. This bistability has been observed in two different wind tunnels for very different upstream conditions. As a main consequence, the zero degree drift angle could be a relevant validation case of unstable flow computation. More tests are carried out to understand and control this particular flow feature.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D backward facing double step with pyramidal shaped nose: (a) alone and (b) on its table during (test 1). Dimensions are normalized by h (the first step height).

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Figure 2

Test 2 on the 3D DBWFS with semicylindrical nose at low Reynolds number: the model is set behind the fan and laser tomoscopy is applied at first step midheight

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Figure 3

At midstep height: evolution against the drift angle of streamlines and isocontour of U/U0 . Data are extracted from the time-averaged PIV fields.

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Figure 4

At the surface: top view of the flowfield behind the first step using the oil-film method for β = 0.2 deg

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Figure 5

A PIV time-averaged field A decomposed as the weighted sum of solutions B1 and B2 : A = αB1  + (1 − α)B2 . Here α = 33% and β = 0.04 deg. Streamlines are in black.

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Figure 6

Evolution of the coefficient α [defined in A = αB1  + (1 − α)B2 ] against the sideslip angle β for test 1 (PIV data) and test 2 (tomoscopy data)

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