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Aerodynamics of biplane and tandem wings at low Reynolds numbers

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Abstract

Experiments were performed to investigate the aerodynamic characteristics of two-wing configurations at a low Reynolds number of 100,000. The wing models were rectangular flat plates with a semi-aspect ratio of two. The stagger between the wings was varied from ∆X/c = 0 to 1.5; the gap was varied from ∆Y/c = 0 to 2 and ∆Y/c = −1.5 to 1.5 for biplane and tandem configurations, respectively, with the decalage angle fixed at 0°. Lift, drag, aerodynamic efficiency and power efficiency ratios show that for small incidence angles, performance compared with the single wing is degraded. However, for single-wing post-stall angles of attack, lift performance improves and stall is delayed significantly for many configurations with nonzero gap, i.e., ∆Y/c ≥ 0. For a fixed angle of attack, there are optimal gaps between the wings for which total lift becomes maximum. Particle image velocimetry measurements show that performance improvement relies heavily on the strength of the inter-wing flow and the interaction of the separated shear layers from the leading edge and trailing edge of the leading wing with the trailing wing. Unsteady forces are found to intensify for certain two-wing configurations. A switching between the stalled and unstalled states for the trailing wing as well as a switching between the merged and distinct wakes is shown to have high flow unsteadiness and large lift fluctuations.

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Abbreviations

b :

Semi-span

c :

Chord length

C D :

Time-averaged drag coefficient

C D1 :

Time-averaged drag coefficient of wing 1

C D2 :

Time-averaged drag coefficient of wing 2

C Dm :

Time-averaged monoplane drag coefficient

C Dt :

Time-averaged total drag coefficient, (C D1 + C D2)/2

C L :

Time-averaged lift coefficient

C L1 :

Time-averaged lift coefficient of wing 1

C L2 :

Time-averaged lift coefficient of wing 2

C Lm :

Time-averaged monoplane lift coefficient

C Lt :

Time-averaged total lift coefficient, (C L1 + C L2)/2

q :

Dynamic pressure

R AE :

Time-averaged aerodynamic efficiency ratio, (C Lt /C Dt)/(C Lm /C Dm)

R D :

Time-averaged drag ratio, C Dt /C Dm

Re :

Reynolds number, ρU ∞ c/μ

R L :

Time-averaged lift ratio, C Lt /C Lm

R PE :

Time-averaged power efficiency ratio, (C 3/2Lt /C Dt)/(C 3/2Lm /C Dm)

sAR:

Semi-aspect ratio

U′:

Streamwise velocity component

u′ :

Standard deviation of streamwise velocity

U ∞ :

Freestream velocity

V :

Crosswise velocity component

v′:

Standard deviation of crosswise velocity

X :

Streamwise/longitudinal coordinate

Y :

Crosswise/transverse coordinate

Z :

Spanwise coordinate

α :

Angle of attack

δ :

Decalage

∆X/c :

Stagger between the wings

∆Y/c :

Gap between the wings

μ :

Viscosity

ρ :

Density

σ CLm :

Standard deviation of lift coefficient for monoplane wing

σ CL1 :

Standard deviation of lift coefficient for wing 1

σ CL2 :

Standard deviation of lift coefficient for wing 2

ω:

Vorticity

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Acknowledgments

This work was supported by the University of Bath University Research Scholarship. The authors would also like to acknowledge the University of Bath’s technical staff for their continued support. The authors also thank the EPSRC Engineering Instrument Pool.

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Authors and Affiliations

  1. Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, UK

    R. Jones, D. J. Cleaver & I. Gursul

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  1. R. Jones
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  2. D. J. Cleaver
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  3. I. Gursul
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Correspondence to I. Gursul.

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Jones, R., Cleaver, D.J. & Gursul, I. Aerodynamics of biplane and tandem wings at low Reynolds numbers. Exp Fluids 56, 124 (2015). https://doi.org/10.1007/s00348-015-1998-3

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  • DOI: https://doi.org/10.1007/s00348-015-1998-3

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