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Help on Venturi Design

 
Old 02-04-2019, 07:23 PM
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Default Help on Venturi Design

Im working on a new splitter for Wee1. Hoping to incorporate WORKING venturis rather than just the 9mm flat Marine ply in use currently.

Im crap with digital drawing so I will try and explain my thoughts using Ryans front splitter as the basis for our new version.

Qualifying thoughts.
  1. With exposed cam gears/belts and being a OCD clean freak, I dont want crap blasting through the engine bay as Ryan suggested happens with his 2017 design. Otherwise i woudl just replicate something similar.
  2. The current flat ply splitter weighs 6.5 KG's...not light. Im hoping that after making a ply/wood version of approx 11kg's that a carbon and foam version made to a similar design will considerably lighter than even the current flat ply in use.
  3. The car sits currently with a 10cm (approx 4") spoiler to ground clearance so I believe getting it closer to the ground is of benefit AND it means we can create a venturi internally to the new splitter and retain the full length flat floor under the engine bay.
    1. i.e. if the new front splitter is 5cm (approx 2") deep we can make the venturi shape internally.
Hopefully the couple of pictures of my ply test below will explain.


Okay, so I welcome advice on the following.

Car could do with some more front DF to balance rear wing. As you can see bottom picture below, it has quite a large centre section venturi.

Should I add two more smaller ones? One in front of each wheel going for "all of it" or is this one centre one a big step in balance change...?

Focusing on the central section. Is a steeper angle more desireable than a longer shallower angle.....I know seperation is an issue but I wonder in this case if my 2" max height over this long distance is a good or a bad thing...?

Ive done a lot of reading and video watching and STILL cant tell if a radius'd curve is better than a sharp break angle. aerodynamically I would have thought a curve but studying Jet Afterburner sections in drag cars etc they all seem to use very sharp transitions...

and PS. Now im worried about ground clearance halving the current 10cm to 5cm. we run 1000kg springs and xidas so maybe a overall ride height raise and use up the last few clicks left to full hard on the dampers to cope. Presumably if it works we would need to up the spring rate again....




Current splitter.


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Old 02-27-2019, 02:28 AM
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The 3rd photo above should have been this one.

and below that is it mocked up to the car.


Upside down showing venturi.

Mocked up to the car.
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Old 02-28-2019, 09:31 AM
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Originally Posted by mx5-kiwi View Post
Car could do with some more front DF to balance rear wing. As you can see bottom picture below, it has quite a large centre section venturi.

Should I add two more smaller ones? One in front of each wheel going for "all of it" or is this one centre one a big step in balance change...?

Focusing on the central section. Is a steeper angle more desireable than a longer shallower angle.....I know seperation is an issue but I wonder in this case if my 2" max height over this long distance is a good or a bad thing...?

Ive done a lot of reading and video watching and STILL cant tell if a radius'd curve is better than a sharp break angle. aerodynamically I would have thought a curve but studying Jet Afterburner sections in drag cars etc they all seem to use very sharp transitions...

and PS. Now im worried about ground clearance halving the current 10cm to 5cm. we run 1000kg springs and xidas so maybe a overall ride height raise and use up the last few clicks left to full hard on the dampers to cope. Presumably if it works we would need to up the spring rate again....
In my experience, the center section does less than ones by the wheel well unless you have a good floor and diffuser to help feed the center diffuser on the front splitter. How many diffuser sections you need will depend on the front splitter height off the ground and how much downforce you actually need. The higher the height, the more expansion the diffuser can handle. For the side front diffusers, I'd purchase off the shelf ones if it were me (if you need the downforce).

The angle would depend on ride height. Higher the ride height, the more angle you will need.

If you are talking about the throat of the diffuser, radiused or sharp doesn't matter. Both can work well, depends more on the design. Do not use jet afterburner for comparison as that is compressible flow and high velocity. The science is totally different.
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Old 02-28-2019, 01:38 PM
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Originally Posted by plucas View Post
In my experience, the center section does less than ones by the wheel well unless you have a good floor and diffuser to help feed the center diffuser on the front splitter. How many diffuser sections you need will depend on the front splitter height off the ground and how much downforce you actually need. The higher the height, the more expansion the diffuser can handle. For the side front diffusers, I'd purchase off the shelf ones if it were me (if you need the downforce).

The angle would depend on ride height. Higher the ride height, the more angle you will need.

If you are talking about the throat of the diffuser, radiused or sharp doesn't matter. Both can work well, depends more on the design. Do not use jet afterburner for comparison as that is compressible flow and high velocity. The science is totally different.
Fantastic, thank you. Much appreciated.

I intend to run the wheel/side venturi as well and have no height limit (unlike the centre section)....So i guess if I build it with the intent to go for as much DF as I can we can then start paring it back from there for balance as required..

Mechanic/Engineer wants to see the engine dry sumped before we go much firther with the front and rear Aero so will dabble with this in the background for awhile.

V2 will be CF and foam sheet, so hoping to drop 2/3's the weight that way.

FYI - I was watching the Supercar Mustang Documentary last night and caught a glimpse of their undertray venturi. that looked to be around 20/23 degrees in the centre section.
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