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Author Topic: Exhaust direction on rear diffuser  (Read 1879 times)
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Slide
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« on: November 01, 2016, 11:49:32 PM »

This is a bit of a non LS question...

On a production based car, but with a flat bottom, front splitter, with a center channel, side boards and then a decent rear diffuser with strats, that start just in front of the rear diff... also a rear wing that lays back about 8 inches or so from body work, and at roof line height.

When plumbing the center exit exhaust into the diffuser, is it better to have it pointed straight back, horizontal or to angle it so the exhaust flow follows the shape of the diffuser?

My imagination makes me think that if it's angled up, not only wil it help pull more air to expansion (the diffusers role) but thenif I can get the flow right, the exhaust at load will push air up to assist in extra flow along the bottom side of the wing, increasing its effect with out drag...

Or am I way wrong here...
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SPARKY
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« Reply #1 on: November 02, 2016, 12:01:50 PM »

ooooo  I like that Question !!!!!!!
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« Reply #2 on: November 02, 2016, 01:11:05 PM »

Check out any of the F1 tech forums for more info. Search "blown diffusers". They were banned because of the increase in downforce. They even worked out a way to keep the gasses pumping out into the diffusers when the engine was off throttle. Look for explanations of hot and cold blown diffusers.
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Paolo Castellano
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« Reply #3 on: January 22, 2017, 11:08:36 AM »

This is a bit of a non LS question...

On a production based car, but with a flat bottom, front splitter, with a center channel, side boards and then a decent rear diffuser with strats, that start just in front of the rear diff... also a rear wing that lays back about 8 inches or so from body work, and at roof line height.

When plumbing the center exit exhaust into the diffuser, is it better to have it pointed straight back, horizontal or to angle it so the exhaust flow follows the shape of the diffuser?

My imagination makes me think that if it's angled up, not only wil it help pull more air to expansion (the diffusers role) but thenif I can get the flow right, the exhaust at load will push air up to assist in extra flow along the bottom side of the wing, increasing its effect with out drag...

Or am I way wrong here...

I spoke with an aerodynamicist who told me that it is best to blow the exhaust at the trailing edge of the diffuser. I had asked him about the Migeot F1 Blown diffuser.

This is what he said:

Airflow will separate from a diffuser very easily, so it must have very gentle changes of direction and minimal features inside. Here are some good examples.

https://upload.wikimedia.org/wikipedia/commons/5/55/Porsche_962_119_diffuser.jpg

http://cdn-9.motorsport.com/static/img/mgl/1600000/1640000/1647000/1647200/1647249/s1_1.jpg

https://michalzolkiewski.files.wordpress.com/2013/11/12.png


I would route it just above the diffuser and flare the ends of the pipes so that they form two wide outlet slots with their trailing edges touching the trailing edges of the diffuser roof. That is the most effective way to implement a blown diffuser. The local airspeed there is lower than anywhere forward of that point, so you get the biggest downforce gain due to exhaust blowing there.
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