Influence of Open-Jet Effects on Vehicle Wind Tunnel Measurements

Christoph Schoenleber; Felix Wittmeier; Jochen Wiedemann

doi:10.4271/2021-01-5014

The wind tunnel is the standard tool in the development and improvement of vehicle aerodynamics. Usually, automotive wind tunnels contain an open test section, which results in a shear layer developing on the edge of the jet. This shear layer brings instabilities that can lead to resonance effects in the wind tunnel influencing the pressure distribution in the test section.

To investigate the resonance effects, the classic wind tunnel corrections were applied to averaged drag measurements recorded in a resonance and nonresonance configuration of the model scale wind tunnel of the University of Stuttgart. The Mercker-Wiedemann-Method shows good compensation for the differing pressure gradients. Pressure measurements on the surface of the DrivAer Notchback model show different separation points on the rear window for measurements in resonance and nonresonance configuration. This means that the resonance effects can influence the separation significantly.

In a second step, the pressure fluctuations in the test section were measured with the dynamic wind tunnel underfloor balance and the surface pressure measurements on the vehicle. The results show good consistency compared to common empty tunnel multi-hole probe measurements. Besides, the resonance events in these results do not lead to a fixed Strouhal number. This is in contrast to other investigations presuming a fixed Strouhal number of 0.48, which means that the shear layer effects do not scale linearly with the velocity. This indicates that several different effects exist.

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Influence of Open-Jet Effects on Vehicle Wind Tunnel Measurements 2021-01-5014

SAE MOBILUS