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Would you mind expanding on those limitations? I am planning to use Solidworks' CFD for my build since I'm experienced with it, but I wouldn't mind investing in something more accurate. What do you use?

I have 3 systems we use .
the 1st and I like the best is ANSYS CFX the cost was well over 20K just for the program and then adding in the cost of the 3D scanner to scan present designs like cars along with some other things your talking north of 70K for every thing . the tech support is one of the best though.

solidworks is OK but just OK it's easy to use and good for the DIY guy . the detail is nothing like ANSYS CFX and that is what I'm saying about limitations . things like air flow and pressures are not detailed enough to give you more of a real world sim of what the air flow is doing in real life . so backing it up with a wind tunnel testing is best for this .

algor simulations is good IMO better then solidworks harder to use but more detailed .

the thing about aero design and sim programs is you get what you pay for .
if your not in the business to design and build aero products then your not competing with other businesses so a free down load or low cost system will be ok .


when it comes to diffusing the under chassis air it starts right at the front of the car and not at the rear .there is also the air flowing over the top of the car and down the sides that effects the diffusers performance .

Here is what i have come up with (@60mph) after days of trying to get the model to work right. There are a lot of surfaces so it was a pain.
You can see where it detaches right before the rear tube on the diffuser.

Having and engine model would be good but i dont have one. And it looks like the wing needs to be pretty high on this design to get clean air.

looks like there is lift too... ; (

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

here is it completely flat. Not sure which way to go as far as a diffuser design is concerned. Thoughts?

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

This has nothing to do with the diffuser, more to do with the wing. I would think that if you're really concerned about aerodomanics, you would model yourself in the car to see how the air flows over you then onto the wing. It looks like in your model you've neglected this.

Yeah i left myself and the seats out because it was crashing the model. SO you are saying a diffuser is pointless and focus on the rear wing?

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

No, just an observation. But, I'm just curious about how fast one needs to be going before the diffuser actually starts to show its worth. I recall reading somewhere that on a street car a diffuser is more of a styling thing rather than a functional part (though I can't remember where i read it).

I was half considering making the underside of my Europa totally flat with a diffuser towards the rear, but then decided it would be best to get the car finished before looking into any more modifications.

i am pretty sure out of all the aero things that can be done.... a diffuser is most effective. Also i am doing the body work now so if need to make changes i would like to do while in process.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

I agree that the diffuser is usually the most effective element for adding downforce to cars. F1 makes most of their downforce from the under-body and diffuser.

Looking at your diagram it looks like the wheels are being treated as stationary objects. The biggest thing you need to consider is that they are rotating. At the top of the tire, the tread is effectively moving at twice the speed of the car creating massive amounts of turbulence. One of the biggest factors in diffuser design is blocking the turbulent air from the tire getting into the diffuser.

I recommend watching some of the videos from these guys both do a great job of explaining many aspects of our cars.
https://www.youtube.com/watch?v=HXxkNF2L__8
https://www.youtube.com/watch?v=gvDerbIU-uY

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

Yeah i know kyle... his shows are awesome.

I can add a boundary condition to the tires to simulate them rolling.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

Interesting... adding the rotational force changed the normal force in Y (downforce) from -10 to -3.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

Putting the bottom of the cockpit in the same plane as the bottom of the suspension box is causing a couple of major problems with your desired underbody aero scheme. First, most 'normal' suspension geometry necessitates that the ground clearance be high enough to kill most underbody aero effects in the first place. Second, it prevents the creation of an effectively shaped diffuser. It also doesn't help that the diffuser section is rather narrow.

From an underbody aero perspective, it would have been much more effective to drop the floor to the same height as the diffuser strakes, and bring the diffuser full width between the rear wheels. Since it's a bit late for that, and considering it appears to primarily be a street car and general high performance toy with inherently poor aerodynamics anyways, I'd say just throw on whatever 'diffuser' element looks the best and move on. There really doesn't seem to be any point in spending a bunch of time doing CFD for the minimal real world gains it will return.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Yes you could be right but this is more for educational purposes and i have always been curious. I highly doubt that the diffuse would last more than 20 on the street ; )

Here is the latest. Trying to block the turbulence from the rear tires seems rather pointless as the tires are so far back. All of the turbulence seems to develop past the rear of the chassis. I am going to try to extend the diffuser back and see if it makes a difference.

The good thing is that the front end channels are huge amount of air right into the scoop.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

Any benefit adding a sealing skirt around the sides to force more air into the diffuser seeing as you are not bound by any rules. I would start them around the middle of the car at the widest point getting gradually taller as they go back towards the diffuser.

If you look at the bottom of F1 cars they have a wide flat floor which is basically just a sheet at the back. If you were to keep the rear section of the floor the same width as the widest point then the shape of your cars body would suck in air to force it over the diffuser acting more like a wing.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

I added a bit more floor under the car and started the strakes in the center of the car and increased them as they went out. This resulted in the force in the y direction going from -20 to 2. Is that right? Should i shoot for a + or - number here?

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.