Quote:
Originally Posted by Phase
i saw that. they mentioned other sources
their testing showed a drag increase on page 13 of the pdf. any idea why their 7 degree diffusers added drag in every single set up?
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* Carr's 'short' diffuser on the Audi 100-III was @ 4-degrees.
* Carr's 'long', lowest-drag diffuser on the Audi 100-III was 2.8-degrees.
* FIAT's lowest drag diffuser was also @ 2.8-degrees.
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Ahmed and Buccheim's prismatic roof angles were all dependent upon their length, as a function of total greenhouse length.
The same may be true of diffusers.
It's going to do with vortex-drag and induced upwash.
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* All 'high-performance' (sic) sports cars design-in extra drag for the sake of high-speed stability.
* All 'low-performance' ( sic) 'economy' cars reject designed-in drag, as a tool for high efficiency.
The fairly-recently-reported, 2013, Cd 0.11, Cambridge University Eco Racer ( CUER ) has a diffuser which angles upwards as much as 9-degrees, however, this curved surface constitutes 79.7% of the car's total length!
University students privileged enough to have access to multi-core processors and industry-grade CFD could devote some time towards parsing out the subtle differences between 'simple' and 'complex' diffuser designs. And do it within the context of low-drag.
And they might want to study a 'real' 'passenger' car, not some simplified data cloud which depicts no real world mass-produced production vehicle we'd ever directly experience.
The Chinese are doing it!