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Base drag reduction by control of the three-dimensional unsteady vortical structures

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Abstract

The present paper deals with the wake of a 2D body equipped with a drag reduction device. The device is a 3D trailing edge consisting of alternate segments of blunt base and spanwise cavity. The aerodynamic mechanisms acting on the near wake are studied in a water tunnel from schlieren observations by thermally marking large scale structures. The results show that the efficiency of the device is directly related to the presence of longitudinal vortices. An optimization of the shapes in subsonic compressible flow had led to a decrease of more than 40% of the total drag of the profile.

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Abbreviations

Δt :

time interval between two successive exposures

H :

base height

L :

chord of the profile

h :

test section width

U :

upstream velocity

v :

kinematic viscosity

p s :

static pressure

p :

upstream static pressure

C p :

mean pressure coefficient defined by \(\frac{{2\left( {p_s - p_2 } \right)}}{{\gamma p_2 M_2^2 }}\)

M :

upstream Mach number

N :

fluctuating pressure frequency

S :

Strouhal number

Pr :

Prandtl number

T :

temperature

T w :

wall temperature

T ∞ :

upstream temperature

T a :

adiabatic wall temperature

n :

refractive index

a :

image source diameter at the knife edge

f :

focal length

c p :

specific heat

\(\eta = y\sqrt {\frac{{U_1 }}{{v_1 x}}} \) :

reduced coordinate along the x-direction

1:

relative to the water tunnel

2:

relative to the wind tunnel

References

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  • Fiedler, H.; Nottmeyer, K.; Wegener, P. P.; Raghu, S. 1985: Schlieren photography of water flow. Exp. Fluids 3, 145–151

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  • Gai, S. L.; Sharma, S. D. 1981: Experiments on the reduction of base drag of a blunt trailing edge aerofoil in subsonic flow. Aeronaut. J. 85, 206–210

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  • Pollock, N. 1969: Some effects of base geometry on two dimensional base drag at subsonic and transonic speeds. Aerodynamics note 316. Australian Defence Scientific Service. Aeronautical Research Laboratories

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  • Schlichting, H. 1979: Boundary layer theory. New York: McGraw-Hill

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  • Tanner, M. 1972: A method for reducing the base drag of wings with blunt trailing edge. Aeronaut. Quart. 23, 15–23

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Authors and Affiliations

  1. Office National d'Etude et de Recherches Aérospatiales, Institut de Mécanique des Fluides de Lille, 5, boulevard Paul Painlevé, F-59000, Lille, France

    O. Rodriguez

Authors
  1. O. Rodriguez
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Rodriguez, O. Base drag reduction by control of the three-dimensional unsteady vortical structures. Experiments in Fluids 11, 218–226 (1991). https://doi.org/10.1007/BF00192747

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  • DOI: https://doi.org/10.1007/BF00192747

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