Quote:
Originally Posted by JulianEdgar
People often see what they want to see.
And what I want to see is a section in any aerodynamics textbook that applies a template as has been so often been encouraged here. Viz:
- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars
I don't know of even one textbook or technical paper that does so.
That's the reality: encouraging people to apply a predetermined shape as some sort of tool to help them in their aerodynamic car modifications is to simply mislead.
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1) One textbook would be, 'Aerodynamics of Road Vehicles', 2nd-Edition, page 185, Figure 4.104.
In 1973, Janssen and Hucho, working on detail optimization of the upcoming 4-door, VW Golf, deviated greatly in terms of style from Giugiaro's original design, obtaining a 33% drag reduction, to demonstrate what could be reached over and above, by departing from the stylistic concept.
Exactly what we here at EcoModder.com endeavor for.
The Golf's drag minimum was achieved when the roofline matched the 'template' profile.( Figure 4.47, page-145 )
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2)* The 2016, Cd 0.19, Mercedes-Benz IAA extensible boat-tail section is a perfect 'template' match, according the Daimler-Benz' wind tunnel photographs and video.
* The Audi E-tron experiences a 20-count drag reduction when the 'raked' roofline is exchanged for the more template-like 'Sportback' roofline.
* The Audi SQ2, for 2019, enjoyed an 'aero improvement' by an elongation of its roof spoiler ( something the Cd 0.27, Mitsubishi Mirage takes to the limit).
* Volkswagen's 1981 Flow-Body ( long-tail ) experiences a 10-count drag reduction when the 'template' is followed to its conclusion ( Cd 0.140 ), Figure 4.120, page- 200, top of upper table.
* The Daimler-Benz, Mercedes-Benz, C-111 III demonstrates a drag reduction, from Cd 0.237, to Cd 0.178, when it's boat-tail 'template' is carried to its conclusion. Figure 4.42, page- 142
* Sunbeam utilized the 'template' for the aft-body of it's SUNBEAM 1000-HP land speed record car of the 1920s.
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3) For notchback spoilers. please see:
1965 Ford Mustang fastback (sic)
1982 Pontiac Trans AM Firebird
1990 Opel Calibra
1993 Volvo ECC
1993 Chevrolet Camaro V-6
1997 Nissan 200SX
1998 Toyota MR2
2014 Audi RS5
2014 Chevrolet Camaro SS 1LE
2015 Alfa Romeo 4C
2015 Lexus RCF
2018 KIA Stinger
2012 Toyota GR SUPRA
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As to assessing the aerodynamic 'purity' of a car, that's kind of subjective, and non-quantifiable.
I'd go no further than 'streamlined.'
Hucho used the terms ' optimum' and 'ideal' interchangeably in his 2nd-Edition.
Hucho explicitly described the streamline half-body as 'optimum'. The reader is free to interpret that adjective as they please.
Other than 'wings', the streamlined body of revolution-based half-body, is the only other path to ultra-low-drag according to Hucho.
The discussion of 'wings' is for it's own dedicated thread.
Without any 'testing' or 'measurements,' I've found the 'template' to be adequate for facilitating land speed records, distance records, and low-emissions records.
For amateur modifications it's shown a propensity for low drag, as a 'first' and perhaps 'last' approximation for streamlining.
