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Measurement of Reference Dynamic Pressure in Open-Jet Automotive Wind Tunnels
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Abstract
In automotive open-jet wind tunnels reference velocity is usually measured in terms of a static pressure difference between two different cross-sectional areas of the tunnel. Most commonly used are two sections within the nozzle (Method 1: ΔP-Nozzle). Sometimes, the reference velocity is deduced from the static pressure difference between settling chamber and plenum (Method 2: ΔP-Plenum).
Investigations in three full-scale open-jet automotive wind tunnels have clearly shown that determination of reference dynamic pressure according to ΔP-Plenum is physically incorrect. Basically, all aerodynamic coefficients, including drag coefficient, obtained by this method are too low. For test objects like cars and vans it was found that the error ΔcD depends on the test object's drag blockage in an open-jet wind tunnel. On the other hand, correct determination of dynamic pressure according to ΔP-Nozzle for car and van testing requires at least a certain minimum distance from balance center to reference-tap location upstream of the nozzle exit.
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Kuenstner, R., Deutenbach, K., and Vagt, J., "Measurement of Reference Dynamic Pressure in Open-Jet Automotive Wind Tunnels," SAE Technical Paper 920344, 1992, https://doi.org/10.4271/920344.Also In
Vehicle Aerodynamics: Wake Flows, Computational Fluid Dynamics, and Aerodynamic Testing
Number: SP-0908; Published: 1992-02-01
Number: SP-0908; Published: 1992-02-01
References
- Müllenbach, P. Deutenbach, K.-R. “Determination of Dynamic Pressure and Reference Pressure in Automobile Wind Tunnels with Open Test Section” BMW Internal Report 1989
- Potthoff, J. Essen 3.-4 November 1987
- Egle, S. Herzum, N. Hofele, G. Konitzer, H. “Wind Tunnel for Aerodynamic Research” SAE Paper 820372 1982
- Vagt, J.-D. Wolff, E. 1987 1987