The forces and pressures on a generic bluff body in ground effect were investigated. The bluff-body model was equipped with interchangeable underbody diffuser ramps and side plates. Five different diffuser angles were tested: 5, 10, 15, 17, and 20 deg to the horizontal. The experiments were undertaken in a low-speed wind tunnel equipped with a moving ground. Load cells, pressure taps, and surface flow visualization were the techniques used to evaluate the flow field. The flow field is characterized by vortex flow and three-dimensional flow separation. A region of hysteresis was found for the 15, 17, and 20 deg diffusers. As the ride height is varied, five different flow types can be identified with three subtypes within the region of hysteresis. The force reduction phenomenon was found to be caused by both vortex breakdown and flow separation.

Issue Section:
Technical Papers
Keywords:
aerodynamics, wind tunnels, flow visualisation, hysteresis, flow separation, vortices
Topics:
Diffusers, Flow (Dynamics), Pressure, Vortices, Flow separation, Flow visualization
1.
George
,
A. R.
,
1981
, “
Aerodynamic Effects of Shape Camber, Pitch, and Ground Proximity on Idealized Ground Vehicle Bodies
,”
ASME J. Fluids Eng.
,
103
, pp.
631
–
638
.
2.
George, A. R., and Donis, J. E., 1983, “Flow Patterns, Pressures, and Forces on the Underside of Idealized Ground Effect Vehicles,” Proceedings of the ASME, Fluids Engineering Division, 7, ASME, New York, pp. 69–79.
3.
Sovran, G., 1994, “The Kinematic and Fluid-Mechanic Boundary Conditions in Underbody Flow Simulation,” Proceedings of the CNR-Pininfarina Workshop on Wind Tunnel Simulation of Ground Effect, Turin, Italy, May, National Research Council.
4.
Cooper, K. R., Bertenyi, T., Dutil, G., Syms, J., and Sovran, G., 1998, “The Aerodynamic Performance of Automotive Underbody Diffusers,” SAE Paper No. 980030.
5.
Cooper, K. R., Sovran, G., and Syms, J., 2000, “Selecting Automotive Diffusers to Maximize Underbody Downforce,” SAE Paper No. 2000-01-0354.
6.
Senior
,
A. E.
, and
Zhang
,
X.
,
2001
, “
The Force and Pressure of a Diffuser-Equipped Bluff Body in Ground Effect
,”
J. Fluid Eng.
,
123
, pp.
105
–
111
.
7.
Senior, A. E., 2002, “An Investigation of a Generic 3D Diffuser in Ground Effect,” Ph.D. thesis, University of Southampton, Apr.
8.
Moffat
,
R.
,
1988
, “
Describing the Uncertainties in Experimental Results
,”
Exp. Therm. Fluid Sci.
,
1
, pp.
3
–
17
.
9.
Polhamus
,
E. C.
,
1971
, “
Predictions of Vortex-Lift Characteristics by a Leading-Edge Suction Analogy
,”
J. Aircr.
,
8
(
4
), pp.
193
–
199
.
10.
Wentz
, Jr.,
W. H.
, and
Kohlman
,
D. L.
,
1971
, “
Vortex Breakdown on Slender Sharp-Edged Wings
,”
J. Aircr.
,
8
(
3
), pp.
156
–
161
.
11.
Lambourne, N. C., and Bryer, D. W., 1962, “The Bursting of Leading-Edge Vortices—Some Observations and Discussion of the Phenomenon,” Aeronautical Research Council, Reports and Memoranda No. 3282.
12.
Zerihan
,
J.
, and
Zhang
,
X.
,
2000
, “
Aerodynamics of a Single Element Wing in Ground Effect
,”
J. Aircr.
,
37
(
6
), pp.
1058
–
1064
.
13.
Burgin
,
K.
,
Addey
,
P. C.
, and
Beatham
,
J. P.
,
1986
, “
Wind Tunnel Tests on Road Vehicle Models Using a Moving Belt Simulation of Ground Effect
,”
J. Wind. Eng. Ind. Aerodyn.
,
22
, pp.
227
–
236
.
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 by ASME
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