Aerodynamics discussion

[Dimman]

Originally Posted by serialk11r

I think the reason those cars went airborne so easily was because they have some kind of stupid mandate on the underbody, something like it has to be flat all the way to the diffuser? I seem to recall these LeMans cars having some giant flat splitter, and they're obviously very low to the ground, so a small angle of attack, and you can run into a lot of trouble.

I would guess that F1 cars don't go airborne since 1. giant wing in front 2. their high noses have a smooth curve channeling air to the underbody.

Yes. And that makes them a good example of what you were saying about airplane wings and ground effects.

The old days before all the neat stuff like active suspension, and sliding skirt venturi tunnel cars sound awesome.

[Shankenstein]

Random thought. I know a full-on active aero and ride-height (like the McLaren 12C) is beyond the DIY capabilities of our community right now... but say we start with an active spoiler (like the Porsche 911).

Does anyone know of a successful (aftermarket) implementation of spoiler angle modulation based on vehicle speed? I'd like to think that we could either use OBD data or ABS speed sensor frequency to determine speed. A lookup table would provide the threshold values and outputs. A basic stepper motor control would manage spoiler attack angle.

If you could "pitch out" at low speeds and in eco-mode, then you could install a monster wing without hurting highway mpg. Similar control could be done on active grille shutters or front aero.

Just thinking out loud.

EDIT: Jackpot! LINK to Supra LINK to Accord LINK to E36

[EarlQHan]

Originally Posted by ayau

What are you using for your model? Is it a computer generated model or a physical model?

It is a computer surface model

Originally Posted by serialk11r

Thanks for doing the testing. Your C_d is lower than the manufacturer claim most likely because you essentially have a sealed front grill (radiator causes drag), smooth bottom, and non rotating wheels.

We are aware of the problems with using the model, but there's still a very strong correlation with the real world values given by Toyota and Subaru. Even though it isn't an exact model, it gives us repeatable, accurate data.

Originally Posted by Shankenstein

Agreed. We have an opportunity to keep this forum untainted and really make something special happen.

EarlQ, the world is a better place because of your work. If you'd be willing to distribute your solid model, I (and others) would be glad to improve it and run a heap of simulations. I'm a MechE that primarily works with Pro/E, and so-so with SolidWorks and Inventor. Minimal CFD, but some magnetic and stress FEA work. If it's validation, we can do that... but I imagine the primary benefit will be identifying "hot spots" and testing solutions for both Eco and Track purposes. Alot of smart folks on here with similar interests.

Unfortunately, I cannot give you our final model because we have done some proprietary work to it. However, this BRZ model can be purchased and is an excellent base http://humster3d.com/2011/12/15/subaru-brz-2013/ You will need to "seal" the surfaces to make the model watertight when doing CFD. We use OpenFOAM, which is open source and free to the public. You do however, the Linux to run it. If anyone were to try and do their own CFD analysis, we could help you get started.

[EarlQHan]

Originally Posted by Shankenstein

Random thought. I know a full-on active aero and ride-height (like the McLaren 12C) is beyond the DIY capabilities of our community right now... but say we start with an active spoiler (like the Porsche 911).

Does anyone know of a successful (aftermarket) implementation of spoiler angle modulation based on vehicle speed? I'd like to think that we could either use OBD data or ABS speed sensor frequency to determine speed. A lookup table would provide the threshold values and outputs. A basic stepper motor control would manage spoiler attack angle.

If you could "pitch out" at low speeds and in eco-mode, then you could install a monster wing without hurting highway mpg. Similar control could be done on active grille shutters or front aero.

Just thinking out loud.

EDIT: Jackpot! LINK to Supra LINK to Accord LINK to E36

Aeromotions has an active wing.

We are working on a proprietary passive system that works purely on air density and vehicle speed

[ultra]

Am I correct to assume that our rear 'diffusers' are mostly cosmetic?

It would be interesting to see the effects of properly sealing off the gap around the rear muffler can using a panel such as the TRD or Borla ones, or even installing a proper venturi-style diffuser which blemds with the underbody.

Looking under the car it's pretty plain to see that somebody's done a good amount of engineering work on the design of all the under panels, vents amd flaps etc. Even the radiator is well sealed from the factory for optimal flow (there's little foam pieces surrounding it).

Beautiful to behold, and great to have on a car in this price range.

Also would seem to be a great starting point for a more elaborate aero setup.

Great thread BTW.

[dasklein]

Originally Posted by Shankenstein

Random thought. I know a full-on active aero and ride-height (like the McLaren 12C) is beyond the DIY capabilities of our community right now... but say we start with an active spoiler (like the Porsche 911).

Does anyone know of a successful (aftermarket) implementation of spoiler angle modulation based on vehicle speed? I'd like to think that we could either use OBD data or ABS speed sensor frequency to determine speed. A lookup table would provide the threshold values and outputs. A basic stepper motor control would manage spoiler attack angle.

If you could "pitch out" at low speeds and in eco-mode, then you could install a monster wing without hurting highway mpg. Similar control could be done on active grille shutters or front aero.

As EarlQ pointed out, Aeromotions has 3 active aero applications that differ by either actuation type (internal/external) or single element vs. split element. We just did a BRZ fitment with our "static" wing which can be seen here: http://aeromotions.com/products/by-c...ic-subaru-brz/

This static fitment can be upgraded to active as well using our external R.Module.

We've also built the active front splitter that you are referring to. We did extensive CFD testing on it, then took it to the WindShear 180mph rolling road wind tunnel where the Nissan Delta Wing was tested. We have some info on it here: http://aeromotions.com/project-cars/...hallenge-aero/

We do implement a Drag Reduction System (DRS) like F1, so that there isn't much of a drag penalty.

One thing to note on our BRZ testing: our airfoil is very unique (even though it looks very basic), and implements a concave pressure recovery system which seems to have a huge benefit with the BRZ shape (the window rake + factory deckled specifically). In static mode, we only need 2 degrees of angle of attack (AoA) to achieve perfect balance. And because of our low drag shape and only needing 2 degrees of AoA, there isn't much of a drag/speed penalty.

[Dimman]

Originally Posted by EarlQHan

It is a computer surface model



We are aware of the problems with using the model, but there's still a very strong correlation with the real world values given by Toyota and Subaru. Even though it isn't an exact model, it gives us repeatable, accurate data.



Unfortunately, I cannot give you our final model because we have done some proprietary work to it. However, this BRZ model can be purchased and is an excellent base http://humster3d.com/2011/12/15/subaru-brz-2013/ You will need to "seal" the surfaces to make the model watertight when doing CFD. We use OpenFOAM, which is open source and free to the public. You do however, the Linux to run it. If anyone were to try and do their own CFD analysis, we could help you get started.

Are all those models the same quality?

There is a GT86 and even an AE86 in the Toyota section.

I've started looking into building a desktop for this and may have some questions for you in a few months.

Thank you very much for sharing!

[Pete156]

Good stuff!

[EarlQHan]

Originally Posted by Dimman

Are all those models the same quality?

There is a GT86 and even an AE86 in the Toyota section.

I've started looking into building a desktop for this and may have some questions for you in a few months.

Thank you very much for sharing!

They are not. I believe the higher the poly count, the better the surface and the tighter the mesh. However, I am not a fluid expert, that is my partner Paul's expertise. I have sent him a link to this thread and hopefully he can chime in and help out.

[djliquidsteele]

Originally Posted by robispec

some real time testing on venting the hood
don't have that fancy F1 paint but at streets of willow there were PLENTY of people kicking up dust when they went Agricultural


YES any air going out the top is air not going out the bottom so less lift up front...

So does this mean any number of the vented hood styles we have seen from Siebon would essentially do the same thing?

[robispec]

Its hard to say because the vent needs to provide a low pressure zone directly behind it other wise the high pressre air on the hood will reflux into the engine bay. Like allthe people who jack up their hoods at the hinge/cowl...this forces air back into the engine bay.

[djliquidsteele]

Is there anyway to tell purely by looking at the design of the hood or is wind tunnel time necessary?

[7thgear]

Originally Posted by djliquidsteele

Is there anyway to tell purely by looking at the design of the hood or is wind tunnel time necessary?

you can assume a certain amount of truth given science, but for absolute certainty you would need testing

although the end goal is improved laptimes, so you can dump a wind-tunnel for an accelerometer and a notepad.

[plucas]

I am EarlQ partner. I am the aero guy who does the aero development and CFD. Also looking at purchasing an FRS....

Originally Posted by Shankenstein

EarlQ, the world is a better place because of your work. If you'd be willing to distribute your solid model, I (and others) would be glad to improve it and run a heap of simulations. I'm a MechE that primarily works with Pro/E, and so-so with SolidWorks and Inventor. Minimal CFD, but some magnetic and stress FEA work. If it's validation, we can do that... but I imagine the primary benefit will be identifying "hot spots" and testing solutions for both Eco and Track purposes. Alot of smart folks on here with similar interests

PM me if you are interested in making a solid model. I can give you a good starting point to work from. I just cannot distribute the model we are currently using. We use Creo/ProE but also have a lot of experience in SolidWorks. Glad to see some other engineers on here with interest in racing cars!

Originally Posted by dasklein

This is a great thread! I'm excited to follow it!

What are you guys using for your CFD sim? I'm definitely interested in seeing the results.

One thing to note about CFD: its not actual "real life" data. Its one of the most ground breaking additions to the design and testing process, but its still a simulation. It's a big misconception that its 100% (or even 99+%) accurate to real conditions. Its all about the software, the 3D model, and how the programmer/aerodynamicist sets everything up.

In the end you still have to get it on the track or in a "real" wind tunnel...

We are using OpenFOAM. Basically we use creo/proE for the cad model, then OpenFOAM for the pre-processing and solver, and then paraview for post-processing. We run this on a linux workstation. Depending on the analysis and its requirements, runs can take anywhere from 12-36 hours.

Correct that cfd is not "real life." It is an experiment with conditions that do not change to get repeatable results. It is in no way 100% and that is a big misconception. However, it can definitely drive quality design changes that drastically improve performance. Most automotive cfd models are very simplified because of computing time and it won't drive design changes on a big scale. How it is set up makes a big difference. I have validated our program and setup using automotive test of ahmed bluff body and a class 8 heavy vehicle (GCM). Both have data from university for validation of setup and program.

Also windtunnels are not "real life" either. That is also a big misconception. It is also just an experiment to get repeatable results that represent what is going on in real life (just like cfd). Both are doing the same thing, just in different ways.

Originally Posted by Dimman

Are all those models the same quality?

There is a GT86 and even an AE86 in the Toyota section.

I've started looking into building a desktop for this and may have some questions for you in a few months.

Thank you very much for sharing!

Not all the models are of the same quality. However, the models still need to be reworked anyways to make them watertight for cfd purposes. If you have any questions on computer hardware or cfd in general, let me know in this thread or pm. I am happy to help :happy0180: