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4th gen aero


boxkita

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Read the Coanda effect article. Takeaways: 1) The front air dam height vs the flatness of the underbelly are related. The air dam causes vortices to occur and air flow stabilizes attaching to the undertray. Reading the pdfs, I'm not convinced the road surface impacts flow/detachment of the air flow from undertray. Alas the undertray is not perfectly flat so flow is not laminar (at least I don't think so, never tested it)

2) Calling the rear spoiler as having the Coanda effect seems a stretch to me. The flow over the roof is laminar. I tested it in various locations (front/rear & side-to-side) and at various speeds (30-100mph) at "h" of 1"-7". The wiki link says a lip causes the vortices (shows a cutout that steps down). A change in direction is not part of the effect, at least not a vigorous one. That's why I thought removing the rear spoiler would make a difference. Instead, perhaps a small cutout where the spoiler is that wraps onto the rear window would cause the vortices and then into the laminar flow? This would be closer to the sedan's rear window structure

 

Ground effect vs undertray vs pressure vs data collected. The 2d model isnt flat. Wondering if the shape is having an effect on the calculated lift? It looks like a venturi to me, which makes the lift numbers expected? Hitting my knowledge limit again.

 

The oem undertray doesn't fit flush with the oem front bumper. There's a notch so air coming under the bumper is somewhat attached to the underside then runs across the notch which indented upwards then the undertray slopes downward and flattens out to roughly the same height as the bumper. It's been widely stated the undertray has a noticeable effect on the draw of the intercooler. This seems like the blown air effect application of Coanda? And why the intercooler doesn't become effective at cooling until 30-35mph?

 

Latching onto random crazy (and reading a bunch of intercooler cooling threads); what if the intercooler fan was placed in the notch? That would create a blown air effect and cause the laminar air flow to reattach or exist as the case may be. The fans would have to draw from somewhere (radiator output?).

Edited by boxkita
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  • 1 month later...

I Just found this thread but its very relevant to my interests, its been about 8 yrs since I had to run lots of CFD on Solidworks. I do have a sw18 license with the full simulation package and am open to help. I do have lots of experience in solid molding just not as much in the simulation side.

 

if I understand the discussion here, I could be wrong its almost 5 and I've been reading project specs all day. is the goal is to reduce flow separation and the "dead" pocket of recirculation at the back of the wagon? outside of just a general understanding of the fluid at play on these wagons?

 

What about putting a vane/spoiler that pulls the high velocity stream off the top of the wagon and redirects it down the window to make the detachment of flow at the rear window not as drastic?

 

I had a Old wagon that we put something like this on and it basically eliminated dust settling on the rear window on dirt roads. would be quick to pop a simple vane into the 2d model and see the impact

. https://roofrack.com.au/product/rear-dust-wind-deflector-1100mm-alloy-universal/

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I'll can add it to the list of things of things I need to do instead of playing shop :lol:

 

Do you know what solver Solidworks uses? Would be interesting to do a comparison of the solution versus what I've been using (ANSYS Fluent). I could send you a .step with the wagon geometry to try if you want!

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Solidworks doesnt give a name on there solver its all native to the software.

 

i would be intrested in a .stp of the wagon to try out. might be a little slow of the start to make sure the solutions are making sense. ill pm you,

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  • 4 weeks later...
finally signed into linkedin after 18 months break. There's a group called "Motorsport Career Advisor"...job listings for motorsports teams. Mercedes, Red Bull, Haas, and others

 

I have aerodynamics degree from lgt.com. Should be worth something to Red Bull or Mercedes.

 

You’re gonna need more yarn.

"Striving to better, oft we mar what's well." - Bill Shakespeare - car modder
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Awesome work you all!

 

Any chance you guys could do a ride height study? Ie: Stock legacy vs 2" lowered vs 2.6" lifted? Mostly interested in 2.6" lifted since that's stock Outback height.

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Awesome work you all!

 

Any chance you guys could do a ride height study? Ie: Stock legacy vs 2" lowered vs 2.6" lifted? Mostly interested in 2.6" lifted since that's stock Outback height.

 

Awfulwaffle did a test on that at one point. .5/.6 inches has no effect. Keep in mind, for most of things we've been postulating, you have to moving fast. 100mph fast. Getting workable data for 60mph was my goal but the number of data runs was astronomical. Awful's company is tolerant but not that tolerant. Getting access to similar resources was/is expensive.

 

A full belly pan is more useful than a wing/splitter. Until you are going fast, at which point, your 16/17 year old suspension components and usually poor tire choices are going to be a bigger part of your handling than any aero will be.

 

Unless you are racing for money, aero is the last thing to change. Mostly because there are more gains to be made elsewhere much more cheaply.

 

If you want to try at home, stop by a car dealership and raid their cardboard stash. CAD yourself some test pieces. Then tape colored yarn over likely surfaces. Add a gopro mounted to view the yarn. Make a run. Look at the video. If the is not flapping, your making progress. Don't get a ticket

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Same for learning cad on a $300 chromebook.

 

Awfulwaffle had school, extra work demands, and then blew up an engine lol. However I think the main issue is that without a cad model the results were both a bit odd and also limited in usefulness.

 

 

Sent from my iPhone using Tapatalk

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Alright well... I guess I'm learning openfoam if my home computer can handle it. Hopefully it's close to Ansys Fluent...

 

So awfulwaffle was only using 2d sketches generated from a picture, no CAD models, right?

 

Do we have any cad models in any format we can try?

 

I guess the end goal is a library of .STL or .Step files, correct?

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Yep, 2D sketches - CAD surfaces generated from FSM side views. Last I looked at it, OpenFOAM implemented many of the same spatial discretization and turbulence models available in Fluent, though maybe to a less sophisiticated degree. Can't recall the options for pressure-velocity coupling and other solver algorithms offhand. I'd love to get it running on my home box as well, and I think it should be plenty usable for 2D runs as well as limited domain studies (ie portions of the engine bay, underbody, etc).

 

Even if we can get 3D CAD geometry, I think we'll have a tough time running full 3D models of a car on any typical local PC. To get meaningful resolution on even a halved/symmetric model, I think we'd be looking at grids on the order of 20+ million tetrahedral elements - maybe as low as 10 million if we do some selective defeaturing and grid coarsening. From experience, grids of this size run pretty dang slow on a local machine, and are memory intensive. For reference - last analysis of this scale I ran locally on my workstation took about a week to run. That machine is a 16 core Xeon box with 128 GB of RAM, and memory load was near 50%. PC sounds like a jet engine and is borderline useless while the solve is running.

 

We could look into polyhedral grid generators, if OpenFOAM supports that type of grid. That will certainly help with element count and solution time, though I don't think it'll really make much of a difference in terms of memory usage if I recall correctly.

 

I'm out of school now and my car hasn't re-exploded again (yet), so I'd love to help get this going again. When I'm overloaded I tend to spend what little spare time I have drinking beers and staring at a wall, which is mostly why I went quiet last time around. Having folks working together will make me feel like a POS for doing that, great for personal motivation :)

 

I do also have the Bluetooth anemometer I bought a while back for this project, for getting some test data.

 

I also believe I owe everyone a 2D parametric study, with an input parameter list that we defined somewhere in this thread.

Edited by awfulwaffle
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You don't owe us anything but we sure do appreciate the knowledge. I don't have the level of computing power needed to run higher end 3D stuff - When I used Fluent it was through a university lab and the lab computers would share the workload between the active and inactive computers - That was 5 years ago and I'm long gone now...

 

I'll see what I can get lined up on the 3d side of things - at least for overall models of things.

 

 

Would this be an option? - $6 a run seems reasonable to me...

https://cfd.direct/cloud/

https://cfd.direct/cloud/cost/

Edited by Rcnesneg
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looks like they improved their cloud products. When I first looked into it, I had access to Azure dev units (unlimited cores/ram). Building the images was a pain and required knowledge I didn't have.

 

From experience with Azure, you can burn money pretty fast depending on the configuration.

 

we had a "let's test this" list that got whittled down. Then exploded as we learned more. Getting a 3d model stalled at "need a scanner".

 

Not sure how I can help other than find resources and funds (maybe). Pretty much everything Awful wrote above didn't even make a sound as it flew past me. :)

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