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......therefore it very difficult to predict drag results?
or is it maybe due to Boussinesq's assumption? which is taken into consideration by up to the 2nd turbulent model in CFD?
iv not tried the Reynolds Stress Model(RSM) but this does not take Boussinesq's assumption into consideration? -Anyone tried this and got accurate drag results?

a6zz wrote:Hi

Is it correct in saying fluent doesnt predict transition from laminar to turbulent very accurately?

Abdul

It does not. However Fluent 12 will have a 4 eqn SST model that allegedly will do so fairly well.

pgj wrote:When the OWG presented its findings, it suggested that CFD models gave diametrically opposite results to wind tunnel models.

Yeap - if those results were the centreline velocity plots presented, they were absolute crap.

The entrainment and energy exchanges in the wake looked all wrong.

pgj wrote: Can anyone explain to a total green-horn how this could happen?

With great ease. Even experienced people can miss out one little thing, and it can snowball into a big problem.

There are dozens of things that could go wrong.

pgj wrote: I am also interested to find out what external/environmental models are used, where they come from, and how they are calibrated.

Sorry, you will have to explain what you mean by external/environmental?


For calibration, there are two base techniques - (1) validate physics, or (2) replicate the a full geometry and compare to (expensive to acquire) experimental data.

Its recommended to do both, as usually (2) will not tally up correctly based on default model properties from commercial codes. Having done (1), you can decompose the errors from (2) and adjust your model appropriately. After that, you need to perform additional tests on separate full geometries to make sure you aren't tailoring the model to 1 result.

a6zz wrote:......therefore it very difficult to predict drag results?

For F1 cars?

It would be irrelevant, as the difference from laminar boundary layers over a centimetre of the car's nose would be minuscule compared to the drag from the car as a whole. You'll have bigger modelling errors (100x) elsewhere.

a6zz wrote: or is it maybe due to Boussinesq's assumption? which is taken into consideration by up to the 2nd turbulent model in CFD?

iv not tried the Reynolds Stress Model(RSM) but this does not take Boussinesq's assumption into consideration? -Anyone tried this and got accurate drag results?

The K-epsilon model does not transport the turbulent shear stresses, which makes it poor for low-Re modelling near the wall in areas near transition and separation. Menter's K-W SST model improves this somewhat, but while it does consider the turb shear stresses to a degree, it doesn't fully do the number crunching behind them.

Dunno about the RSM model, cannot comment.

sorry if this not the place to ask a general question, but didnt think it worthy of a new thread.
now i hear aero guys and engineers talk about "points" of downforce. So, what exactly is a point?

Is there any free way into CFD for me to do a couple of simulations on my desktop computer???

Just to see how a couple of ideas would work, dosnt have to be a massivly good pro programme, just give a idea wether it would work.

Yes there is!! There is something called OpenFoam, Google it i've been desperately trying to get it to work on a version of linux of got installed but it doesn't have any sort of unzipping software. I've got a Race in just over a month and am yet to make the body, would LOVE to test it before hand.

I'm a little concerned that areas of the tail will be too steep and that air may start to "fall away" If anyone can offer any assistance it'd be greatly appriciated.

But yes anyway Open Foam, looks really good and I belive has been mentioned several times on here before it's just getting the Bugger to work!!

Any free CFD software that can be used for Windown XP, as i dont have access to any Linux computer.

Linux can be free and is realllly easy to use runs surprisingly smooth as well i've found. I've got a version of Xandros Presto, It gives me the option when I boot up to either boot linux or xp

@Greenpower
Having taken a (mostly stupid) look at their website for the last like 50 minutes gives me a good reason why you didn't
Seems far from being starter-compatible.

@ESPImperium
Don't bother with that. I'm sure that's not what you are looking for (and me too).

Guys,

Look here for parrallel processing applications that run on Microsoft Windows (the HPC version) http://www.microsoft.com/hpc/en/us/supp ... tions.aspx

G

hi everyone, first post here.

i am so in love with your pictures and discussion and i want to join you. to you can give me any advice how to start something like this? espacially i am interested in a free cfd-program (perhaps free for students?) with some good tutorials...

fbn wrote:(...) i am interested in a free cfd-program (perhaps free for students?) with some good tutorials...

http://www.ansys.com/Products/ed.asp

not free, but price is really low. of course you can find absolutely free version somewhere in the internet...

if you need more you can write your own procedures in Fortran and easily add them to the package. several years ago I was doing this kind of stuff to simulate casting processes, when I had to merge flow with heat transfer.

what is the difference between ANSYS ED and ANSYS FLUENT?

Hi everybody,

I´m looking for some help in respect to undertray production.

I designed an undertray for Mitsubichi Evo IX and at this moment I need some advise in a manner to produce a stifnees enough undertray.

Anybody produced an undertray and could let me know what is the number o layers and the density of each one to produce a good undertray?

Thanks in advance!

Ivan