The force and pressure behavior of a generic diffuser in ground effect were investigated. The diffuser model is a bluff body with a rear diffuser at 17 deg to the horizontal, and side-plates. Measurements were conducted in a low speed wind tunnel equipped with a moving ground facility. Techniques employed were force balance, pressure taps, and surface flow visualization. The diffuser flow in ground effect was characterized by vortex flow and three-dimensional flow separation. Four types of force behavior were observed: (a) down-force enhancement at high ride heights characterized by an attached symmetric diffuser flow, (b) maximum down-force at moderate ride heights characterized by a symmetric diffuser flow and separation on the diffuser ramp surface, (c) down-force reduction at low ride heights characterized by an asymmetric diffuser flow and flow separation, and (d) low down-force at very low ride heights, also characterized by an asymmetric diffuser flow and flow separation. The down-force reduction near the ground is attributed to flow separation at the diffuser inlet and subsequent loss of suction in the first half of the diffuser.

Issue Section:
Technical Papers
Keywords:
aerodynamics, flow visualisation, flow separation, vortices, wind tunnels, pressure measurement, force measurement
Topics:
Diffusers, Flow (Dynamics), Pressure, Vortices, Flow visualization, Flow separation, Suction, Separation (Technology)
1.
George
,
A.
,
1981
, “
Aerodynamic effects of shape, camber, pitch and ground proximity on idealized ground-vehicle shapes
,”
ASME J. Fluids Eng.
,
103
, Dec., pp.
631
–
638
.
2.
George, A., and Donis, J., 1983, “Flow patterns, pressures, and forces on the underside of idealized ground effect vehicles,” Proceedings of the ASME Fluids Engineering Division Symposium on Aerodynamics of Transportation-II, Vol. 7, Dec., 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.
4.
Cooper, K., Bertenyi, T., Dutil, G., Syms, J., and Sovran, G., 1998, “The aerodynamic performance of automotive underbody diffusers,” SAE Paper 98-0030, Jan.
5.
Brundrett
,
E.
, and
Baines
,
W.
,
1964
, “
The production and diffusion of vorticity in duct flow
,”
J. Fluid Mech.
,
19
, pp.
375
–
394
.
6.
Burgin
,
K.
,
Adey
,
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
.
7.
Moffat
,
R.
,
1988
, “
Describing the uncertainties in experimental results
,”
Exp. Therm. Fluid Sci.
,
1
, pp.
3
–
17
.
8.
Maltby, R., and Keating, R., 1962, “Flow visualization in wind tunnels using indicators,” AGARDDoraph, Apr. pp. 29–38.
9.
Morel, T., 1978, “The effect of base slant on the flow pattern and drag of three-dimensional bodies with blunt ends,” Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles, Plenum Press, New York, pp. 191–226.
10.
Reneau
,
L.
,
Johnston
,
J.
, and
Kline
,
S.
,
1967
, “
Performance and design of straight two-dimensional diffuser
,”
ASME J. Basic Eng.
,
89
, pp.
141
–
150
.
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