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 10-05-2009, 06:51 AM #1 (permalink) Piwoslaw aero guerrilla     Join Date: Oct 2008 Location: Warsaw, Poland Posts: 3,686 Svietlana II - '13 Peugeot 308SW e-HDI 6sp 90 day: 58.1 mpg (US) Thanks: 1,266 Thanked 716 Times in 454 Posts Sedan drag reduction with special spoiler This is a section from the book I recently acquired: An important parameter in researching the aerodynamics of sedan-style vehicles is the effective angle of slope, measured from the rear of the roof to the rear of the trunk. The above drawing (according to Nouzawa et al.[2]) shows how Cx increases depending on the effective angle of slope. Notice the similarity to the angle of slope in a hatchback, which has a minimum around 12 degrees and a maximum around 28 deg. Two ways of improving Cx is to either extend or to raise the trunk lid. Fukada et al. ([1]) noticed that Cx could be reduced by adding a deflector to the central section of the rear edge of the trunk lid. A spoiler on the whole width of the rear edge produces a large downforce, increasing drag, but a small (1/3 width of trunk) deflector gave half the downforce and a reduction of drag (compared to no spoiler at all). The reason for this is as follows: the body of a sedan produces a pair of trailing vortices and the small deflector produces vortices of the opposite direction of rotation, thus partially cancelling the first pair. This lead to the idea of building a triangular-shaped deflector on the trunk lid to use as a vortex generator. The drawing below shows how drag Cx and lift Cz depend on the width of the deflector. [1] Fukada H., Yanagimoto K., China H., Nakagawa K., Improvement of vehicle aerodynamics by wake control, JSAE Review 16 (1995), p.151-155. [2] Nouzawa T., Hiasa K., Nakamura T., Kawamoto K., Sato H., Unsteady-wake analysis of the aerodynamic drag on a notchback model with crotical afterbody geometry, SAE SP-908, paper 920909, February 1992. Attached Thumbnails       __________________ e·co·mod·ding: the art of turning vehicles into what they should be What matters is where you're going, not how fast. "... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell [Old] Piwoslaw's Peugeot 307sw modding thread
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