| ON THE NEAR-WAKE OF A GROUND-EFFECT DIFFUSER WITH PASSIVE FLOW CONTROL |
| Obinna Ehirim1, Kevin Knowles1, Alistair Saddington1, Mark Finnis1, Nicholas Lawson2 |
1Cranfield University
2Cranfield University |
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| ABSTRACT |
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A ground-effect diffuser is an upwardly-inclined section of an automobile’s underbody which increases
aerodynamic performance by generating downforce. To understand the diffuser flow physics (force behaviour, surface and offsurface
flow features), we established the near-wake (within one vehicle width of the base) velocity profiles and flow
structures of an automotive ground-effect diffuser using a bluff body with a 17 degree slanted section forming the plane
diffuser ramp surface (baseline geometry), and endplates extending along both sides of the ramp. Wind tunnel experiments
were conducted at a Reynolds number of 1.8 million based on the bluff body length, and laser Doppler velocimetry was used
to measure two-dimensional velocity components on three planes of the diffuser near-wake. We also measured the velocity
field in the near-wake of diffusers with modified geometry (with an inverted wing or a convex bump) as passive flow control
devices. The near-wake velocity profiles indicated that the passive flow control methods increased the diffuser flow velocity
and that the longitudinal vortices along the diffuser determined the shape of the flow structures in the near-wake of the diffuser
bluff body. |
| Key Words:
Laser doppler velocimtery, Ground effect, Diffuser, Flow control |
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Corresponding Author.
Alistair Saddington , Email. 
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