Boxster 986 Aerodynamics @180km/hr

[Duezzer]

This has to be one of the coolest threads I have ever seen - So very very interesting in so many ways.

[Nine8Six]

Originally Posted by rs10

Sounds like you have some amazing tools at your disposal! Not that I can follow every detail of course, and I’m particularly puzzled about one thing.

I understand you are doing virtual aero modeling/testing using computational fluid dynamics. But you also mentioned putting a pressure plate/sensor under each wheel. You also have access to a windtunnel? Or … ?

Also, the 15 degree test at 160kmph you mentioned sounds like driving 160 with a 40+ kmph sidewind. That’s rather quick, so no wonder you got a left/right bounce! But I wouldn’t worry about experiencing anything like that when cornering at 160, as what is happening in the air should be quite differernt, no? For instance, suppose that on a 160 kmph corner you cross a line on the track perpendicular to your direction of travel. If your car is cornering neutrally, then the air that passes exactly over the center of your car when the front wheels cross the line will also pass exactly over the center of your car when the rear wheels cross it (Well, ignoring how the air might get pushed to the side forwards by the car). That’s quite different from a side wind. (And also rather different from going straight. As the front and rear of the car pass the same line, they will be further to the outside. And as the middle passes it, it will be further to the inside.)

Also, even if what happens in the air were the same as with a side wind, 15 degrees is quite a lot. Suppose it was exactly like a side wind (with I can only imagine happening if you have four wheel steering such that the car stays pointing in the same direction, but it moves 15 degrees to the right or left). The wheels would have to be turned at least 15 degrees for that to happen, so your steering wheel would have to be turned, I don’t know, 240+ degrees? I would definitely worry about that at 160!

Admire your knowledge; Clearly there are two kind of people. Some that are clueless and need CFD tools to aquire understanding and knowledge, and some cool others who can compute nearly all of this stuff out of the head. Fascinating thread indeed!

No 'physical' wind tunnel here, you asked.

That virtual wind tunnel/CFD data (results) was exported into spreadsheets then called back into a totally separate structural analisys. That cfd data can be re-used for e.g. excitations or forced displacements if you prefer. Post structural analisys is meant at solving mostly displacement, force and strains/stress problems on the car componets.

So... set evironment; gravity, humidity, temp, and you can predict the behaviour of lets say; your suspension's preload/compression, damping, the force generated on any brackets, your mirrors' mouting points... stuff like that. You can also predict response dynamics (modal) such as vibrations onto body panels (accoustics) and some other more adv nonlinear problems eg. elasticity, buckling, laminates/ply; how much is my 5mm thick cheap fiberglass front bumper is bending at 200miles an hour (seriously lol).

All started from a 180km/hrs beaten up air fluid data mapped node-by-nodes onto a Boxster car! My training folder is now at 30+ gigabytes of raw *.dat text files bud

Learning the fun way! Chk back in two years... I'll be the official 986Forum Formula 1 Team Aerodymics - adviser

[Gilles]

Originally Posted by jb92563

Glider pilot, so I'm very familiar with spoilers and how they effect lift on wings.
.

Jb92563

If you are a licensed pilot, would you consider taking me for a ride on a rented G-102/103 at Warner Springs?

I live in OC and could do a nice drive down Highway 79 and perhaps having lunch afterwards at Ramona?

Regards, Gilles

PS: Sorry for hacking this great tread, just could not resist

[JayG]

Originally Posted by Gilles

Jb92563

If you are a licensed pilot, would you consider taking me for a ride on a rented G-102/103 at Warner Springs?

I live in OC and could do a nice drive down Highway 79 and perhaps having lunch afterwards at Ramona?

Regards, Gilles

PS: Sorry for hacking this great tread, just could not resist

I'll go for a glider ride as well

[rs10]

Originally Posted by Nine8Six

You are welcome for those 'genreric' air flow visuals! I plan on doing the 996 but will post using my RL account under the same alias. I'll shoot you a PM to let you know where to find those. As for messing-up with aero; I think it is fair to say that Porsche have carried out this work and have designed the car to safety limits already Any modification can be costly if not validated indeed. So best to stick to what the pro (Porsche) recommends loll

If you’re also planning on doing something 997 related, well, I’ve done my homework on the Sport Classic and I have a suggestion for you.

The Sport Classic is the only 996 or 997 with a duck tail – on other cars it wasn’t even an option. As far as I can tell, the closest equivalents to the 997.2 Sport Classic are the 997.2 C4 GTS and the 997.2 C4S with the X51 powerkit. All three are wide bodies, and will have larger air intakes in the front bumper than normal Carreras. (The next closest match is the 997.2 C4S without the powerkit, though not sure if the bumper, radiators, etc. are the same.)

The C4 GTS has a Cd of 0.30, versus the Sport Classic’s 0.32. It’s easy to blame the duck tail, but it could also be the double bubble roof or the aftermarket looking side skirts. And I’m not sure the bumper is the same either. It would be very interesting to see what your software shows about both drag (where the difference is) and lift.

By the way, the GTS was available with and without a GT3 style wing (which was probably an option on C4Ss as well). Comparing eiher version to the Sport Classic would be hugely interesting. And if you will be modelling enough cars to do all three rear ends (normal, duck tailed, and winged), then you’d have all the rear aero answers!

Anyway, much though I’d love to see the aero analysis of my car, as you’ve probably guessed, I’d give my vote to the Sport Classic. And I’m betting I’m not the only 996 (or 997) owner who would do the same.

[Robert986]

I guess I´m not the only one who isn´t too pleased with the visuals of the original wing. From a visual standpoint I think this one is the best I´ve seen (my personal preference): http://pictures.topspeed.com/IMG/crop/201012/first-generation-por-4_1600x0w.jpg

Even if I still would like to modify it, I think it has the right thing going for it. Anyway, since I´d except the Porsche guys to have made their homework I´d hesitate to make any changes without some fluid-dynamic calculations to back it up. Great to see this initiative from Nine8Six, I´m hoping for some more conclusions regarding the rear wing vs aftermarket stuff.. My dream product would actually be a carbon fibre rear hatch with included (good looking) wing with a mechanical raise-function like the one on the Turbo.. Unfortunately I don´t think I have the ability to produce it myself, at least not the time..

Again all credits to Nine8Six, lifting the forum to another level

[notech]

This thread is awesome! Would it be possible to make those drawings with "humps" on?
interested to see if they provide any aerodynamics changes.