Front End Aerodynamics - How Different Setups Effect Drag and Lift

[eric6]

Yesterday it was brought to our attention on Instagram that we aren't that active on the forum. And you know what, he was absolutely right. I'm here to attempt and change that. We will actively work on bringing new data aerodynamically that should help the community further the platform and decrease their times around the track. With any luck we will have a new thread every 3-4 months that should raise some interesting discussions .

Before we start, for those of you who do not know about Velox, we are a small group of motorsports engineers who enjoy designing parts on the side for street cars with the hopes to do it full time someday. We would rather not argue about the validity of the data we show, and if you do question our abilities, please refer to this blog post CFD Analysis on Perrin LMP1. I will do my best to answer questions as they come, but @plucas will likely have to answer the more difficult questions. He is the one who does all the aerodynamic analysis.

This first thread is easy as we already had the data from another CFD analysis for a friend of ours. In this thread we hope to give you a glimpse into how different front end aerodynamics effect a street car. This is a tough situation to discuss without an example. The example will be a 1990-1997 Mazda Miata. The Miata was chosen because, we have the model, different designs are common place, and the results are comparable to our cars.



1. Stock 1990-1997 Mazda Miata
2. Stock 1990-1997 Mazda Miata at a 4in Ride Height
3. Small Front Air Dam at 4in Ride Height
4. Small Air Dam with Splitter at 4 in Ride Height
5. Large Air Dam at 4in Ride Height
6. Large Air Dam with Splitter at 4in Ride Height

Note: The air dam and/or splitter is 2 inches off the ground in study 3-6

The solver used for these analysis were a steady state incompressible solver with a k-omega SST turbulence model. OpenFOAM was used for pre-processing and solving and all post-processing was done using Paraview and excel.



Cd = coefficient of drag
Cl = coefficient of lift
L/D = lift divided by drag / aerodynamic efficiency
Downforce: Negative numbers indicate lift, positive numbers indicate downward force.

Drag between all setups are all fairly close with the least drag being the setup with the large front splitter with air dam. The two splitter designs also make significantly more downforce than the air dams alone. The two stock Miata setups make lift instead of downforce. This is expected since most street cars create lift from the factory. These are numbers and trends for common design choices. Actual designs should be more refined after a design goal is formulated.

The stock Miata simulation (CFD run) had a calculated coefficient of drag of 0.36. The 1990-1997 Mazda Miata had a published coefficient of drag of 0.38. The CFD case having slightly lower drag is expected from the simplification of the vehicle vs. the real car. These simplification, primarily the under body, the wheels, and no internal flow, decreased the drag coefficient from published values by 0.015. To us, this puts the coefficient of drag between the simulated value and known value within a reasonable error to continue onward. To reiterate, it passes the “sanity” check to ensure validity in the data.




These photos really emphasize how different setups effect the pressure at the front of the car and midway on the car.



These pictures show how the setups influence how fast the air moves around the car. What is interesting is how much the setups on the front change the airflow behind the car.

Take a close look at all of the photos. Each one paints a different picture and changes how the car reacts when driven at speed. So, which one is best? Their really is no “best” design. Their are compromises for each design. Multiple things should be considered when designing a system. Things like L/D, downforce, and aero balance should be considered. These can and likely will change from track to track and from car to car. It is generally recommended to decide on the rear aero first, and then design the front to balance the car back out.

Please let us know if you have any questions below. Thank you for your time.

[continuecrushing]

wow, tons of info in there!

[Jawnathin]

Great stuff, thanks for posting.

Pardon the silly question, but what is the downforce measured in? Pounds? The unit of measurement wasn't clear.

Can the front bumper of a Miata or 86 support 193lbs without additional support? I figure it would deform the bumper without a brace or some sort.

[Calum]

Excellent info, as always. Just a couple of questions. Why does the coefficient of drag go up from stock to 4in ride height? Is a 4in ride height higher or lower than stock, and by how much?

[TRD_Demon527]

a large amount of information on this thread. i wouldnt mind seeing some test results on the frs/brz/gt86 platform.

[eric6]

Originally Posted by Jawnathin

Great stuff, thanks for posting.

Pardon the silly question, but what is the downforce measured in? Pounds? The unit of measurement wasn't clear.

Can the front bumper of a Miata or 86 support 193lbs without additional support? I figure it would deform the bumper without a brace or some sort.

Unit of measure would be pounds, that wasn't clear, good catch. This is 193 pounds on the entire vehicle, not just the front bumper. On our splitter analysis, it is very interesting to see how much effects the front vs. the rear, as a splitter doesn't effect just the front.

Taken from this informative packet: http://www.ft86speedfactory.com/inst...86Raceinfo.pdf

The front splitter and how it reacts from a stock car:
- Drag Force Decrease from stock: 0.24%
- Total Downforce Increase from stock: 260.13%
- Front Downforce Increase from: 185.04%
- Rear Downforce Increase from: 485.49%
- Total Downforce Increase from stock: 43 lbs

The race upgrade, which has vanes on the underside, increases rear downforce even more.
- Drag Force Increase from stock: 5.00%
- Total Downforce Increase from stock: 362.85%
- Front Downforce Increase from: 211.87%
- Rear Downforce Increase from: 815.99%
- Total Downforce Increase from stock: 60.1 lbs

Additional support was needed for our FT86 splitter at greater then highway speeds which is why we created the race upgrade.

Originally Posted by Calum

Excellent info, as always. Just a couple of questions. Why does the coefficient of drag go up from stock to 4in ride height? Is a 4in ride height higher or lower than stock, and by how much?

4" height is actually lowering the Miata. Paul will be able to tell you why it happens better then myself. We witnessed the opposite occur when we tested the FT86 with the splitter.

Originally Posted by TRD_Demon527

a large amount of information on this thread. i wouldnt mind seeing some test results on the frs/brz/gt86 platform.

We have done quite a bit of testing with the FT86 platform. We will continue to expand our knowledge as time permits. It was suggested we do a write-up on rake and how that effects the vehicle. That will be one of our next threads .

[eric6]

If anyone else has suggestions for future R&D, let us know as well.

Don't be scared to ask questions either.

[Takumi788]

Can Velox do no wrong? I think I am subscribed to every thread you have ever created.

[eric6]

Originally Posted by Takumi788

Can Velox do no wrong? I think I am subscribed to every thread you have ever created.

Thank you

[tnle]

Absolutely love these reads, much appreciated guys!

[plucas]

Originally Posted by Jawnathin

Great stuff, thanks for posting.

Pardon the silly question, but what is the downforce measured in? Pounds? The unit of measurement wasn't clear.

Can the front bumper of a Miata or 86 support 193lbs without additional support? I figure it would deform the bumper without a brace or some sort.

Yes it is in pounds. It needs a lot of support to keep from deflecting. This was ran to find the best setup for my friends Miata.

Originally Posted by Calum

Excellent info, as always. Just a couple of questions. Why does the coefficient of drag go up from stock to 4in ride height? Is a 4in ride height higher or lower than stock, and by how much?

The 4in ride height is lower than stock. I do not remember what the stock ride height is honestly. I would have to go into the CAD model to find out. We measured the height on his car, and then I set the 4in ride height based on what he wanted to run ride height wise.

Why does the coefficient of drag go up in test #2 compared to test #1? Basically when the car was lowered, the front bumper interaction with the rotating front tires increased the drag significantly. This interaction wasn't nearly as profound with the car at stock ride height. With the air dams, the flow characteristics changed decreasing the drag by directing air in different locations.

Full Undertray car:
As ride height decreases : usually drag will increase and so will downforce
As ride height increases : usually drag will decrease and so will downforce

Going from a car with no undertray to an undertray, drag will be decreasedand downforce will increase.

[VerusEric]

I've had a few PM's asking how this would apply to the ZN6 platform. The same laws and rules apply to both vehicles. For those DIY'ers, this gives an idea of what to do and how it affects the whole car.

Because of where it is located (in the front), these results are typical of any car out there.

Hope that clears up a few things . Thanks for reading guys.

[brn12345]

This is a great post!!! It would be much more useful though if the model was an actual BRZ/FRS. The Miata is an early 90's car and had no factory aero bits as with the BRZ/FRS. Our cars already have a significant flat bottom, air channels, front diffuser, etc. In the interest of performance gains it would be useful to run this model with a BRZ/FRS.

[ATL BRZ]