Thread: Wind tunnel use in 2008
3rd Dec 08, 18:53 #21
3rd Dec 08, 19:43 #22
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CFD is comparatively cheap. It certainly saves the manufacture of a lot of components that may be of no use when the analysis is done in the wind tunnel. But it comes at a price of reliability; developing an in-house code from scratch that requires a) taking a CAD geometry, b) meshing it to give a high quality computational grid, c) solving the governing equations on that grid to a good degree of accuracy and d) post-processing the results is not the work of a moment. As I said above it takes years (and I'm not kidding either) to do this. No F1 team has that kind of time to burn so buying in commercial codes is clearly the best plan. In addition to the availability of commercial codes (such as Fluent, Star-CD, CFX etc.) the numerical models in those packages are more than adequate for the speed and efficiency of simulations required for industrial CFD. The general rule of thumb is that flow solutions on complex geometries should take no longer than 24 hours to be produced from point a) to point d). That's a pretty big challenge even with today's computer power hence they buy those ridiculously big computers to do the runs.
The point about accuracy is that you can do a fully time-dependent simulation of a F1 car now if you want - you'll only need the biggest supercomputer in the world and about 50 years to run the simulation. Evidently that's impractical so shortcuts must be made through modelling assumptions. The levels of accuracy of these models in CFD are as follows:
1. Euler solutions: Viscosity is assumed to be zero hence boundary layers do not form near solid surfaces. Very crude but useful for high speed flows like that around aircraft. Produces a steady-state (i.e. average) solution. Runs on a coarse grid and very cheap to compute.
2. Reynolds-Averaged Navier-Stokes (RANS): Effects of viscosity included, hence an improvement over Euler methods. Again produces an average flow solution - many physical processes are smeared out. Needs a finer grid than Euler and is more expensive.
3. Large Eddy Simulation (LES): Time-dependent method where the Navier-Stokes equations are solved exactly above some filter width (usually defined by the computational grid). Below this filter width the scales of motion are modelled using an algebraic function. Needs a much better-resolved grid than RANS and is significantly more expensive. However the results obtained from LES have a much better basis in physical reality than the above two methods.
4. Direct Numerical Simulation (DNS): Navier-Stokes equations are solved for all scales of motion. Grid spacing must resolve the smallest turbulent scales in the flow, typically around a micrometer in size. Stupendously expensive. Very accurate.
Academics perform simulations using 4. on simple things like flows in a pipe, turbulence behind a wire grid, simple boundary layers over a flat plate and so on. It's used to study fundamental turbulence and is of absolutely no interest to industry for the next 20-30 years (at least). Technique 3. is just starting to creep into industry as it costs a hell of a lot less than 4. and offers a reasonable prediction of the real flow physics, although industrial engineers mistakenly think there is little benefit in 3. over technique 2. RANS is now almost standard in industry, with 1. being used mainly in aerospace design for "quick-and-dirty" calculations. The point I'm trying to make here is that accuracy and computational turn-around time are very much interwoven. F1 can't afford to do the highly accurate, time-dependent simulations that 3. and 4. could give them, hence they turn to more crude modelling (mainly 2.), but implicit in those modelling assumptions are things than can be misleading if their effects on the flow are not fully appreciated. This is why no CFD code in existence can be trusted implicitly and the results from CFD must be complemented by wind tunnel test results.
Back to the point of the topic and why I raised CFD in the first place; restricting wind tunnel testing will make teams use CFD more, but for the moment there is no substitute for tunnel testing and if it is limited then it will affect their rate of development.
4th Dec 08, 09:50 #23
4th Dec 08, 11:52 #24
I guess I was looking to it purely from an academic POV and this might not be financially effective for an F1 team.
Even now I would use 1 and 2 to get a general idea about all the aero solutions, scrap the solutions that are useless or with minimal benefit and than go with 3 and 4 to refine the useful ones, but I realize that this approach isn't best suited to an F1 team.
4th Dec 08, 12:52 #25
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9th Dec 08, 11:48 #26
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9th Dec 08, 12:15 #27
9th Dec 08, 12:34 #28
No, you're still alone in a universe of "1" ioan
Renault are not developing a CFD application from scratch but are working with Boeing to refine their models which is what Andrew and I were suggesting.
No F1 team would develop an application from scratch but partnering with one of the largest Aeronautical corporations out there is entirely logical.
Hoffman said: 'The joint Boeing/RF1 team has improved the efficiency of Boeing's CFD software in large part due to the massive size of the RF1 full car model. The size of these car models required refinement of the Boeing CFD software that has resulted in faster run times on Boeing projects. Faster run times allow more iterations and improved designs.
'There are many similarities in the technologies required to develop world-class racing cars and aerospace products. Boeing and RF1 are keen to learn from our respective industry experience so that we can incorporate this knowledge into our overall company efforts to become more lean and efficient.'
9th Dec 08, 14:15 #29
Just in case you missed it:
The size of these car models required refinement of the Boeing CFD software that has resulted in faster run times on Boeing projects. Faster run times allow more iterations and improved designs.
9th Dec 08, 14:32 #30
Personally, I would assume that the Boeing developers are refining the code as it would make no sense whatsoever for them to allow Renault to mess about with it.
Boeing have their own processes and expertise that will need to be followed for development. In fact, I think one of my colleagues in Irvine sold them their CM software a decade ago that they could possibly still be using
You don't understand SW development projects ioan. Boeing will have invested $millions on their source code and might very well work with Renault. Renault will have a high quality tool that they can manipulate to their specific requirements very cost effectively.
Please don't think that they are building this from scratch though as they are just developing a branch tuned to Renaults requirements.
9th Dec 08, 15:07 #31
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- Sep 2001
Yeah it will be the software that is being refined of course. Parallel implementation and efficiency are the most likely areas of development, as splitting up a ~500 million cell grid effectively and having all the CPUs talking to each other with as little overhead as possible is very difficult indeed. The key points are:
"Mistral is expected to increase the CFD capability of the group at one-quarter of the cost of a wind tunnel. The Renault F1 team have reduced full car simulation turnaround time by a factor of three, and increased CFD computational output by a factor of 20."
"Hoffman said: 'The joint Boeing/RF1 team has improved the efficiency of Boeing's CFD software in large part due to the massive size of the RF1 full car model. The size of these car models required refinement of the Boeing CFD software that has resulted in faster run times on Boeing projects. Faster run times allow more iterations and improved designs."
They certainly won't be writing a code from scratch, it'll be optimisation of existing architecture. As for who out of the two are doing the developing, I wouldn't like to guess. There are several areas of licensing and Intellectual Property that are a minefield in collaborative efforts like this - I'm sure they have it all worked out though!
9th Dec 08, 15:40 #32
As for SW development knowledge, FYI I am developing FEM codes for thermo-mechanical processes, so let's say I know way more than you might be able to guess about this area.
Next time, don't tell others what they know and what they don't before you don't know squat about them, that's a friendly advice.
9th Dec 08, 15:51 #33
Originally Posted by Knock-on
IMO the code is being changed/improved, not the models.
But hey, each to his own domain, in my case numerical methods development and implementation, in your case "?".
I'm pretty sure that the guys at Renault are the ones further developing the Boeing code and Boeing are ripping the rewards, as it would make no sense whatsoever for Boeing to develop their own code for Renault while they are not willing to get into F1 anytime soon.
9th Dec 08, 16:36 #34
The model on that occasion was for the key contractor to protect their application and have a 2nd slave system controlling the transfer of information from sub contractors, suppliers, fabricators and main contractors. In this instance, no IP was shared apart from basic interface linking.
I doubt that this is the case in this instance.
What I would assume is that a few Boeing developers working in conjunction
with Renault engineers will create a branch development. What basically happens is that 99% of the standard code is used. However, when code needs altering, it's checked out, altered and checked back in. What this means is that you have two parallel editions of the code with exactly the same backbone but different version numbers. These can be developed as 2 different products but at any time, the branched versions can be deleted or incorporated into the master code to maintain a single enhanced version.
The advantages are that any changes do not effect existing customers codes when upgrading live versions, any enhancements can benefit the core product when fully tested and Renault can have a very cost effective tailored version adapted to their needs and no IP leaves Boeing's systems.
9th Dec 08, 16:45 #35
I'm sorry ioan, you have demonstrated you have no clue whatsoever about SW development projects.
You may be able to mess about chucking a few bits of code together but are completely out of your depth.
It's not a problem. I haven't a clue what FEM entails and wouldn't dream of contradicting you. Perhaps that's because I know my limitations.
9th Dec 08, 16:51 #36
According to the quotes from the above article, the code is being improved to make it efficient for Renault's use and this will be also used by Boeing as it gives them a much better performance than the previous version.
As I see it, the new version can do everything the older could and more and also faster.
As for intellectual property implications, I bet they found a way to agree about the use of the said code.
9th Dec 08, 16:56 #37
Be it as you wish, I'm not going lose my time arguing with someone who doesn't understand the basics of the software we are discussing here.
You might be good at packaging software (or bits of code as you call them) together and talking about intellectual property, but when it comes to CFD or FEM implementations I won't hold my breath with you.
FYI I'm writing writing the codes, not chucking them together.
9th Dec 08, 19:28 #38
Can you guys talk about the issue , rather than engage in this peeing contest , please ?
Seems to me they are using the same base codes , to mutual benefit .
Seems like , since Boeing sounds like they have been using the code for a while , likely longer in the tunnel , have shared thier software , and now are reaping the benefit of that association .
F1's high speed development has the simulations running faster , and both parties are happy .
Faster simulations mean tweaking the tunnel software to relay reliable info faster as well , and with tunnel restrictions , I should think it's where a lot of work is being done , at all the teams ."No pen , no pen ." -what Sato said to me .
9th Dec 08, 21:56 #39
It seems that the models used for the F1 simulation are much more fine and complex and thus they had to improve code in order to get shorter computation times, which benefits Boeing who at their turn will be able to have much shorter computation times with their less complex models.
Not knowing exactly what approach the other F1 teams take I don't know if Renault will have an advantage or not, but it certainly seems they are doing everything to get in that position.
PS: Sorry for the off topic posts, but someone seems to only feel good when he can prove how good he is and how others know nothing when in fact he has no in depth knowledge whatsoever about the discussed topic.
10th Dec 08, 00:01 #40
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- Sep 2001
Yeah but like I said above, Boeing might only be using modelling technique 1 and maybe 2 at the most. Renaults will definitely be using RANS so speeding up the parallel implementation of Boeing's code is of mutual benefit.....