Aerodynamics of the Puma

[Sjoerd]

Hiya,

Over the last year or so I have made a lot of calculations/simulations on the Puma's aerodynamics. I wanted to figure this stuff out before I could start a dynamic simulation of the vehicle on track. Here I will post the results I found. As it has become a rather large document I will take a few days to translate for you.
Please note: I am convinced the values are close, however as I needed to simplify my model they are definately not exact.

The Dutch version of my report:
https://drive.google.com/file/d/0B5ppq8KytvZ_bHFOREZGTkFfMFU/view?usp=sharing" onclick="window.open(this.href);return false;

 

[Sjoerd]

Problem statement:

The sporty coupé Ford Puma that I have in my possession I'd like to use for racing. Therefore I will optimise as much as possible. The 'feeling' exist that the rear of the vehicle creates a lot of lift. Unknown at this time is the aerodynamic balancing of the vehicle. Any further improvements will need to be investigated.


Goals:
- Accurately model the vehicle in CAD-software.
- Make a CFD-analysis of said vehicle.
- Calculate effects of aerodynamics on the dynamics of the vehicle.
- Find possible improvements and implement them.

 

[Sjoerd]

Starting point

To get a clear insight into the aerodynamic behaviour there are two possible ways of investigation:
1. Create a model and do wind tunnel analysis (very expensive & complicated).
2. Do a CFD-analysis using a CAD-model of the vehicle.

I opted for option 2 (for now) for financial reasons.
Using measurement data taken from my vehicle and data obtained from Ford I have constructed said CAD-model. Then I used Solidworks Flow to create the aerodynamic modelling. The CAD-model has been simplified in certain areas. This will be discussed below.

Vehicle model
Starting point is a Ford Puma, modelyear 1999. Using photo's, drawings and existing models I have created this model. It is +/- 1 mm accurate on the center line of the vehicle. Unfortunately the software available to me can not handle a full 3D-model.

 

[Sjoerd]

Simulation parameters

To make accurate comparisons I have used the following data in all simulations:
- Vehicle speed = 55 m/s
- Air pressure = 1012hPa
- Air temperature = 20 graden Celsius of 293K
- Air Humidity = 50%

Model
The constructed model on a 1:1 scale looks as following:

For comparison:


Tomorrow more pages from my report

 

[ArtfulHussy]

Will be following this with a lot of interest! :grin:

 

[Wild E. Coyote]

Grippy stuff! Well done! Watching and waiting with interest!

 

[Sjoerd]

Thanks and hopefully I will not disappoint you. I have gotten it checked by some former teachers the other day, they said it seemed pretty close to reality Next phase is to construct a wind tunnel (thinking +/- 1:28 scale) to verify this properly. Hopefully I will be able to get it started end of the week.

 

[PumaJay]

be interested to see the results and and ideas I can steal for my own car.

 

[corley]

Looks like a cool project mate - good luck!

be interested to see the results and and ideas I can steal for my own car.

Now theres honesty you cant beat

 

[PumaJay]

no point bluffing, might as well be up front

 

[Noobrider]

Couple of things to consider though -

1. The rear suspension is set slightly higher than the front as standard
2. The rear bumper creates a lot of drag
3. 55 m/s = 123 mph - the car wont be going this fast in a corner where the aero is needed most
4. The "feeling" it generates lift is probably more around lift off/braking oversteer.

Compenstation to make to eradicate the "feeling"

1. lower the entire car but make the rear around 20mm lower than the front
2. Fit an EVO style/height spoiler to capture the airflow breaking off the roofline
3. cut holes in the rear bumper or design/fit a rear diffuser

Will be very interested in you wind tunnel modeling results though to disprove my theory.

 

[Cartman]

Grate job

 

[Sjoerd]

Analysis of starting situation (standard vehicle)

Plotted has been the air speed over the vehicle:

Clearly visible is the front of the vehicle slowing the airflow down slightly. When the airflow hits the roof it is in a laminary flow with the highest speed and therefor the highest air pressure. The effects at the rear of the vehicle are opposite, the airflow slows down and enters a turbulent flow with low speed.

The following image shows the air pressures around the vehicle:

The pressures at the front of the vehicle has increased by 15 hPa to a total of 1028hPa. The top of the vehicle has a pressure of 991hPa. Total pressure difference is 37hPa.

 

[Wild E. Coyote]

According to this analysis the aerodynamics look balanced

 

[TGPlayer1]

This may as well be written in French.

Although i like the pretty colours...

 

[Wild E. Coyote]

It is fairly simple. The lower the pressure the higher the lift the car generates. In ideal world you would want donwforce across the car with the pressure points at the axles.
In real world, however, every car (bar the F1 and other similar vehicles including the WRC mashinery) generates lift at higher speeds. On some cars that lift can be nasty (say original Ford GT40 at Mulsanne had so much lift at front that the car wouldn't corner propely; the drivers had to start braking to bring the front end down a bit to negotitate a turn), original audi TT had so much lift at rear that after some people got killed in high speed Autobahn accidents Audi had a recall and put on all cars rear spoiler. That would be seen in graphic like this as low pressure area at the rear end of car

 

[Sjoerd]

Bear with me over the coming period.
Indeed this analysis shows an unbalanced vehicle. In fast corners this became obvious to me. I made a high speed slide at Döttinger Höhe at the 'Ring a few years back. I couldn't explain it at the time but further high speed driving on the Autobahn seemed to point to rear axle lift at speed.
In this report I will calculate the amount of lift at both axles as well. At 55 m/s the standard vehicle theoretically creates 716.5 N of upwards lift. The effects on vehicle dynamics will be calculated as well. I am in the process of verifying this using a full 3D suspension model in MSC Adams. This will need a lot of time though as I have to model it just right. It isn't the handiest job as I will need to dismount parts of my car for measurments (and I need to give some beers to the head of our Quality/Measuring department ).

 

[Sjoerd]

This may as well be written in French.

Although i like the pretty colours...

Can I help you? I'd be more than willing to explain it. I know as an engineer I speak a different language than most practical guys. Though we definately need you guys too :wink: Which parts don't you understand?
Shall I send you some (e-)books on basic aerodynamics?

 

[Z-fella]

Interesting, I am keen to see how a front splitter would change the air flow. Could you do that?

 

[TGPlayer1]

This may as well be written in French.

Although i like the pretty colours...

Can I help you? I'd be more than willing to explain it. I know as an engineer I speak a different language than most practical guys. Though we definately need you guys too :wink: Which parts don't you understand?
Shall I send you some (e-)books on basic aerodynamics?

I wouldn't waste your time. I know how to drive them and I know how to fix them, and that's enough to keep me busy. But I'll keep an eye on this thread, you never know I may learn something.