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Old 10-29-2006, 10:48 PM   #26
Muzz
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Default Re: Diffuser design (descartesfool)

yeah ive heard good things about that book, ill definatly be getting it before i finalise my design. Reguarding fences in the diffuser, which would be the best way to do it.... im guessing just having them run flat with the undertray?

Click the image to open in full size.

And also, how far apart should they be spaced? is there a minium distance or anything?

Heres a rough drawing of my design so far.
Click the image to open in full size.
For the 24" section, i was thinking of splitting that into three 8" wide sections, or should i split it into four 6" sections.

Also with the 10" end sections (which are partly behind the wheels) should i split them into two 5" sections using fences, or leave them as is?

Same with the 11" sections which are at a lower angle (between 3-8 degrease) to alow room for he exhaust, should i split them into 2 sections using fences, or leave them as is?

Or should i just make it as it is in the picture, test the flow directions using oil on the diffuser surface (with the undertray and splitter inplace of course), get some photos for u guys so u can help me make an informed decision where the fences are needed?
Thanks guys
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Old 10-29-2006, 11:19 PM   #27
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Default Re: Diffuser design (Muzz)

Quote:
Originally Posted by Muzz
Also reguarding setting a good angle (ive designed it so both H & D can be easily adjusted allowing angles from 5-25 degrees and adjustable inlet area).

Using tufts along the top surface, i take it you would travel at your max speed, increasing the angle each run until flow seperation begins, then back the angle off to the previous setting so no seperation is experianced at max speed??

how can u tell when seperation is occouring using the tufts??? im guessing that the tufts downstream from the flow seperation will be blowing in all directions, while the unseperated airflow will just blow the tufts toward the rear?
Before answering your final question, lets take a look at this set of questions.

In many cases, the maximum downforce on a body has some symmetrical 3D flow in the diffusers with separation. This seems wrong to many people, but when you realize that downstream of separation, the flowfield pressure is reduced significantly from a case of just a turbulent boundary layer. We already know that the wake region behind a bluff body is very low pressure (relative to static pressure), which is chiefly responsible for the large drag experienced by bluff bodies. Of course, for the same reason, at this high level of downforce the drag is significant especially for large diffuser ceiling angles, which is evident from performing the surface integral of the pressure in the direction of the moving vehicle (i.e. drag calculation).

If your car does not have a large drag budget to work with, then I would not even consider operating the diffuser anywhere close to the maximum downforce condition. You'll be fast in the corners, but also you'll be giving that advantage back everwhere else on the track thanks to the high drag. Also, it is very important to have a flat bottom in front of the diffuser that shields the exhaust, shift linkage, unibody panels, ect. from the high speed air that will result from using the diffuser in the first place.

Can you give anymore specifics about the car, such as power, weight, drag coefficient Cd, splitter and airdam type, whether you'll be running lowered side skirts, and types of circuits you'll be running including the top and average speeds. These questions really should be addressed before a set design is put into place, unless of course you make the diffusers completely adjustable in terms of ceiling height.

I will be leaving for SEMA in Vegas tomorrow, so I will be checking in sporadically to see what is happening with this thread. Hope this all helps.

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Old 10-30-2006, 04:45 AM   #28
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Default Re: Diffuser design (Johnny Mac)

Quote:
Originally Posted by Johnny Mac

Can you give anymore specifics about the car, such as power, weight, drag coefficient Cd, splitter and airdam type, whether you'll be running lowered side skirts, and types of circuits you'll be running including the top and average speeds.
Unfortunatly many of these questions I cannot answer as i have yet to race on a track, i am currently only autocrossing to gain some skill driving (my mum and girlfriend both want me to wait till ive been driving for 2 years before i get out on track, im currenty only 19).

Powerwise i cant really say what my goals are, as i have no idea what say 300whp feels like in a civic, but i plan to build a highly strung N/A for the car so id guess somwhere between 200-300whp.

Weight- yet to strip the car as it is a road car, but the majority of my effort to build a top notch race car will be focused on striping everything, swiss cheesing anything i can, removing non-structal metal wherever possible, lexan windows then building it up again strictly using only what needs to be there.
Being an EK hatch it weighs 1030kg (2270lb) so im hoping to bring it down to say 900kg (1985lb) if possible.

Cd - i havnt tested this yet, but it is on the plans so i can at least compare before and after with undertray and diffuser.

Airdam and splitter - i plan to just extend the stock bumper down and have the splitter coming out say 4" or so. like so...
Click the image to open in full size.

The undertray and also the diffuser heights/angles will be completly adjustable.
Click the image to open in full size.
The red points in the pics are where the height can be adjusted. so i can completly adjust the inlet area, diffuser angle, undertray height/rake and match the splitter to the undertray etc..
As of yet the splitter will be at a fixed height, but im sure i can over come this when i look into it a little more, maby just make up different spacers between the bumper and splitter, id like to have it all completly adjustable.

As far as skirts, they be as low as they possibly can without scraping too often im hoping 1"-1.5" from the ground, along with the diffuser endplates. Theyll be made of thin aluminium sheeting around 1/16" so its cheap and also easy to replace the skirts and endplates, and being thin, they will crush easily if they scrape or get crushed in an off so as not to transfer to much force to the diffuser or undertray.
Click the image to open in full size.
Click the image to open in full size.



Modified by Muzz at 5:56 AM 10/30/2006
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Old 10-30-2006, 04:52 AM   #29
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Default Re: Diffuser design (Muzz)

i cant tell u much about the tracks i would be racing at the majority of the time (queensland raceway, australia also morgan park), as i have only been there to watch others. but here is some info from there site.
Click the image to open in full size.
Click the image to open in full size.



Modified by Muzz at 9:16 AM 10/30/2006
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Old 10-30-2006, 05:14 AM   #30
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Default Re: Diffuser design (Johnny Mac)

Quote:
Originally Posted by Johnny Mac

Also, it is very important to have a flat bottom in front of the diffuser that shields the exhaust, shift linkage, unibody panels, ect. from the high speed air that will result from using the diffuser in the first place.
this is how it will look from the bottom, hopfuly a little less wonky Click the image to open in full size.
Click the image to open in full size.

the only places that arnt covered are the front and rear lca's, however they dont actually extend below the underbody.

thanks for helping me out Click the image to open in full size.


Modified by Muzz at 9:14 AM 10/30/2006
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Old 10-30-2006, 09:23 AM   #31
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Default Re: Diffuser design (Muzz)

im shur there will be many people who come across this post and think "wat a noob , he wants to make a diffuser for his car and has never even raced on a track yet, a diffuser is the last thing to think about" i kno id probably think that.

to these people i just wanna restate that it wont actually be used on my car for a very long time yet, maby even never. im designing and making these pieces as that is what i hope to be doing when i finish my motorsport engineering degree, designing and creating quality racing and suspension components, i get a huge buzz designing things.

I wanna be one of the best racing car preppers/builders in australia, and want to use the civic as my demo car to show of my work in chassis and suspension preperation. I dont see anything stopping me from building the fastest time attack style EK civic in aust (well not at the moment, ive still got endless amounts to learn.Click the image to open in full size..), capable of pulling off crazy fast laptimes with a pro driver.......

So please dont go judging me as a silly noob (im just a plain noob Click the image to open in full size. )who hasnt driven on track and thinks he should use a diffuser on his otherwise stock car, or as somone who is bulding a superfast race car then using it to learn how to race as i am neither of these.

ohh i almost forgot, a big '**** you' to the keyboard cowboy who sent me that extremly stupid IM (you know who you are) what the hell were you thinking Click the image to open in full size.

thankyou
Murray




Modified by Muzz at 1:14 AM 10/31/2006
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Old 10-30-2006, 03:37 PM   #32
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Default Re: Diffuser design (Muzz)

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