BigMike's Forum

Automotive and Theory => Aero and Fluid Theory => Topic started by: BigMike on March 30, 2010, 10:29:28 PM

Title: MR2 MK1 Rear Diffusers
Post by: BigMike on March 30, 2010, 10:29:28 PM
Here is what I got so far..

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear01.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear02.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear03.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear04.jpg)

This, THIS is AWESOME:

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear05.jpg)

These last two are StyleAuto rear bumper kit. I know they aren't diffusers, more like "turbulentors", but I thought I would add them to the thread anyway.

This red car has a Lotus Elise exhaust system:
(http://bigmike.marlincrawler.com/images/areo/diffuser_rear06.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear07.jpg)
Title: Re: MR2 MK1 Rear Diffusers
Post by: BryanH on March 31, 2010, 12:43:19 AM
Wouldn't we have to have a flat floor for a diffuser to do any good? 
Title: Re: MR2 MK1 Rear Diffusers
Post by: BigMike on March 31, 2010, 08:48:22 AM
note: I am at work and typed this up in between distractions and work little bit at a time. So sorry if this reads poor or doesn't make sense. I'll proof read it later tonight.


Wouldn't we have to have a flat floor for a diffuser to do any good?

That would create less drag to the car but the concept would remain the same.


This is how I understand it. Try to think of only the air on the road. The air is sitting still on the road ahead of the car. Let's call this point 1. As the car travels through the stationary air, the air is pushed and accelerated by the car. Some distance behind the car this accelerated air has returned to zero velocity and becomes stationary again. Let's call this point 2.

Frontal air is pushed under the car creating a high pressure area beneath the car. Air traveling over the car has to travel a distance greater than the air under the car. This increases its velocity, and as a result, it's pressure decreases. When the two air streams meet up at the back of the car, they clash with each other as well as clashing with other surrounding air that is stationary (not in the path of the car) (creating turbulence).

The diffuser diffuses the differences in pressures by rapidly increasing the amount of space beneath the car. By rapidly increasing the volume to which the high pressure air is pushed into, likewise, the velocity of the air is rapidly decreased. This is great because we want to leave the air stationary at point 2 like we found it at point 1.

As for the ribs or fins, that is just to aid in straightening and directing the airflow in a linear path tangent to the car's direction of travel.

So the job of a rear diffuser is to help air decelerate back to zero as soon as possible by providing a decompression zone at the back of the car. Of course the back side of the car has a volume much larger than the space under the car (it's infinite!) but because the bumper is so short and there is no underbody areo parts, the air is experiencing turbulence before it reaches the large volume behind the car which takes time for it to self-diffuse. This is why diffusers need to be long and have a gradual slope to them.
Title: Re: MR2 MK1 Rear Diffusers
Post by: BigMike on March 31, 2010, 08:50:00 AM
Here are some visuals already posted (http://bigmike.marlincrawler.com/forum/index.php?topic=40.0):

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear_various01.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear_various02.jpg)

(http://bigmike.marlincrawler.com/images/areo/diffuser_rear_various03.jpg)
Title: Re: MR2 MK1 Rear Diffusers
Post by: Sirdeuce on April 03, 2010, 11:39:09 AM
Use rear wing as diffuser? One on top, one on the bottom.
Title: Re: MR2 MK1 Rear Diffusers
Post by: Sirdeuce on April 18, 2010, 12:06:28 AM
Route air from under car through trunk out tail light holes and cut out license area.
Title: Re: MR2 MK1 Rear Diffusers
Post by: BigMike on April 18, 2010, 01:45:33 PM
hahaha that would be awesome
Title: Re: MR2 MK1 Rear Diffusers
Post by: Sirdeuce on April 19, 2010, 12:11:24 PM
route air through cockpit out rear window hole. 5 gallon bucket scoops replacing B-pillar windows..........
Title: Re: MR2 MK1 Rear Diffusers
Post by: BryanH on April 20, 2010, 01:22:57 PM
We should totally put an F-Duct/RW80 on the car, even if it doesn't work. :)
Title: Re: MR2 MK1 Rear Diffusers
Post by: BigMike on April 20, 2010, 09:07:27 PM
We should totally put an F-Duct/RW80 on the car, even if it doesn't work. :)

Very i-n-t-e-r-e-s-t-i-n-g.....

(http://scarbsf1.files.wordpress.com/2010/03/sauber_f_duct.jpg)

(http://images.planetf1.com/10/03/800x600/McLaren-rear-wing_2428956.jpg)