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Research Papers: Flows in Complex Systems

Characteristics of Boundary-Layer Transition and Reynolds-Number Sensitivity of Three-Dimensional Wings of Varying Complexity Operating in Ground Effect

[+] Author and Article Information
Luke S. Roberts

Aeromechanical Systems Group,
Centre for Defence Engineering,
Cranfield University,
Defence Academy of the United Kingdom,
Shrivenham SN6 8LA, UK
e-mail: l.roberts@cranfield.ac.uk

Mark V. Finnis

Aeromechanical Systems Group,
Centre for Defence Engineering,
Cranfield University,
Defence Academy of the United Kingdom,
Shrivenham SN6 8LA, UK
e-mail: m.v.finnis@cranfield.ac.uk

Kevin Knowles

Aeromechanical Systems Group,
Centre for Defence Engineering,
Cranfield University,
Defence Academy of the United Kingdom,
Shrivenham SN6 8LA, UK
e-mail: k.knowles@cranfield.ac.uk

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 6, 2015; final manuscript received March 10, 2016; published online June 3, 2016. Assoc. Editor: Feng Liu.

J. Fluids Eng 138(9), 091106 (Jun 03, 2016) (10 pages) Paper No: FE-15-1541; doi: 10.1115/1.4033299 History: Received August 06, 2015; Revised March 10, 2016

The influence of Reynolds number on the aerodynamic characteristics of various wing geometries was investigated through wind-tunnel experimentation. The test models represented racing car front wings of varying complexity: from a simple single-element wing to a highly complex 2009-specification formula-one wing. The aim was to investigate the influence of boundary-layer transition and Reynolds-number dependency of each wing configuration. The single-element wing showed significant Reynolds-number dependency, with up to 320% and 35% difference in downforce and drag, respectively, for a chordwise Reynolds number difference of 0.81 × 105. Across the same test range, the multi-element configuration of the same wing and the F1 wing displayed less than 6% difference in downforce and drag. Surface-flow visualization conducted at various Reynolds numbers and ground clearances showed that the separation bubble that forms on the suction surface of the wing changes in both size and location. As Reynolds number decreased, the bubble moved upstream and increased in size, while reducing ground clearance caused the bubble to move upstream and decrease in size. The fundamental characteristics of boundary layer transition on the front wing of a monoposto racing car have been established.

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Figures

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Fig. 1

Diagram of (a) single-element wing, (b) multi-element wing, (c) cross section view of single- and double-element aerofoils, and (d) formula One wing

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Fig. 2

Single-element wing: variation with ground clearance (h/c) of (a) downforce and (b) drag at varying Reynolds number

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Fig. 3

Suction-surface flow visualization of single-element wing. Flow moving from top to bottom, wing tip on the right (h/c = 0.3125, Re = 2.03 × 105)

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Fig. 4

Multi-element wing: variation with ground clearance (h/c) of (a) downforce and (b) drag at varying Reynolds number

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Fig. 5

Flow visualization of (a) suction surfaces and (b) pressure surfaces of multi-element wing (h/c = 0.3125, Re = 2.44 × 105)

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Fig. 6

Suction-surface flow visualization of multi-element wing at h/c = 0.3125 for varying Reynolds numbers (a) Re = 1.63 × 105, (b) Re = 2.04 × 105, and (c) Re = 2.44 × 105

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Fig. 7

Formula-one wing: variation with ground clearance (h/c) of (a) downforce and (b) drag at varying Reynolds number

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Fig. 8

Suction-surface flow visualization of formula-one wing at h/c = 0.3125 for varying Reynolds numbers (a) Re = 1.63 × 105 and (b) Re = 2.44 × 105

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Fig. 9

Flow visualization of F1 wing suction-surfaces (top) and inner endplate (bottom) at (a) h/c = 0.125 and (b) h/c = 0.3125 (Re = 2.44 × 105)

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Fig. 10

Reynolds-number dependency of downforce and drag coefficients of (a) single-element wing and (b) multi-element and F1 wing configurations (experimental, percentage difference between Re = 2.44 × 105 and 1.63 × 105 results)

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