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Couple of questions about 60% wind tunnel models


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#1 JSDSKI

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Posted 18 October 2013 - 22:59

Could one of the forum engineers provide some insight into how teams scale the "60% model" test results to predict the results on a "100%" F1 car?  

 

Do they use standard texts or tables? 

Does each team create their own secret formulas? 

And, is this more experience, practical knowledge from previous seasons... is it more art than calculation?

 

 

And secondly, do the teams also test individual parts, like a front wing, as a 60% model or would they build the 100% size wing.  Or both? I'd guess they'd want to test the new r&d parts on a complete car - so they'd use the scale model. And then test the real part at a race.  Anyway, thanks...


Edited by JSDSKI, 18 October 2013 - 23:00.


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#2 saudoso

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Posted 19 October 2013 - 13:05

This one is bout ship hull performance prediction but covers the basics.

 

I'd say "And, is this more experience, practical knowledge from previous seasons...", it is more art than calculation.

 

 

5.6.3 Turbulent flow assumption

The last assumption regarding the viscous resistance is the assumption about fully developed turbulent flow. However, most Reynolds numbers present in model scale suggests laminar flow around the hull. To correct for this, it is common to apply a turbulence stimulator on the model. This normally consists of a nylon thread, sand strip or similar devices to "disturb" the *ow, and hereby forcing it from laminar to turbulent. Hence, when applying the turbulence stimulator it is also applied an added resistance. To take this into account, the turbulence stimulator are usually placed at a certain distance from the bow, and the lack of turbulence in front of this are assumed equal to the added resistance created by the presents of the turbulence stimulator.

 

 


Edited by saudoso, 19 October 2013 - 13:07.


#3 DogEarred

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Posted 19 October 2013 - 15:06

Could one of the forum engineers provide some insight into how teams scale the "60% model" test results to predict the results on a "100%" F1 car?  

 

Do they use standard texts or tables? 

Does each team create their own secret formulas? 

And, is this more experience, practical knowledge from previous seasons... is it more art than calculation?

 

 

And secondly, do the teams also test individual parts, like a front wing, as a 60% model or would they build the 100% size wing.  Or both? I'd guess they'd want to test the new r&d parts on a complete car - so they'd use the scale model. And then test the real part at a race.  Anyway, thanks...

 

 

 

 

Yes 'JetSki', it's a mixture of all things and the 'scaling factor' is a fairly common formula. Each tunnel though, is different and a great deal of time & effort is put into measuring results consistently. - That's the Holy Grail. Rolling roads that can yaw & adaptive walls all help to achieve realistic results. The best models can steer, pitch, roll & yaw & even blow hot air through the exhaust pipes. All good for measuring transient conditions such as turning into corners, braking & acceleration effects on the underbody aero, crosswinds etc. Tyres are pneumatic & designed the replicate the 'squished' shape they take on - very important, believe it or not.

 

Model sizes have increased over the years & 60% was a size that some better off teams felt they could justify & afford. (Requires vastly stronger model & support components & more power to run the greater volume of tunnel air consistently. Indeed, the bigger tunnels that are used in F1 require electricity generators that could easily power a small town.

 

These days, most areas of the car are simulated by 'full size' CFD before being verified with tunnel parts. (One organisation claimed to design a sports car using CFD only. They managed to keep secret the fact that there was a wind tunnel program going on in another country..)

 

Running wings & other components on their own isn't particularly helpful because every component has effects on other components. A front wing for example will have effects that influence the rear of the car. Most things are looked at in the whole.

 

Those mechanical components that can be, are tested in the R&D department before being signed off for testing at the track. (Usually in the Friday practices.) The effects of aero component parts can only be finally verified on car & it's not unusual for new components to be junked when the effects are not what they were predicted to be. Loadsamoney is wasted on wind tunnel components - but that's development & the spend is justified by results.

 

The F1 cars being designed for 2014 will require more work because of the changes to engine & ERS. This will require greater than the iterative changes that relatively stable rules have promoted. These rule changes will affect chassis rear, & side pods particularly. So there will be plenty of different solutions going on next year.

 

The results from 60% models are considered good enough not to need the greater expense & complication of larger models, or even full size.

 

The F1 rules are now that 60% is the maximum allowed, 'wind on' time is restricted, the air speed is restricted & there is a trade off between CFD & tunnel development. There is plenty of wind tunnel capacity going spare now after some huge investments by some teams.

 

Full sized cars have been used in the past, to verify things but you need a bigger rolling road & have the problem of tethering them. There's a lot of mass & energy to dissipate if something breaks. You'd be shocked if you could see the damage even a 60% wheel & tyre can do, if it breaks loose & goes spinning down the tunnel!

 

Hope I didn't bore you with stuff you already know.

 

Regards

 

DogEarred



#4 bigleagueslider

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Posted 20 October 2013 - 02:14

The analytical tools currently available to F1 teams are actually quite good.  I'm not an aero engineer and have never worked in F1, but I would imagine that the primary purpose for wind tunnel testing is to validate and calibrate the analytical models.  It is now far cheaper and much faster to do aero design digitally.  In fact, I believe it is also now possible to do fairly complex coupled analyses that combine both structural and aero effects.



#5 DogEarred

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Posted 20 October 2013 - 15:22

The analytical tools currently available to F1 teams are actually quite good.  I'm not an aero engineer and have never worked in F1, but I would imagine that the primary purpose for wind tunnel testing is to validate and calibrate the analytical models.  It is now far cheaper and much faster to do aero design digitally.  In fact, I believe it is also now possible to do fairly complex coupled analyses that combine both structural and aero effects.

 

 Indeed that's largely true & as CFD & FEA programmes improve, the cost effectiveness will eventually improve also.

 

Current CFD still requires high computing power, expensive, time consuming & not available to all teams. As you say results are not yet sufficiently reliable to dispense with tunnel verification.



#6 desmo

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Posted 20 October 2013 - 22:44

Why not outlaw tunnel testing altogether and mandate shared open source CFD on restricted computational FLOPS?  You'd potentially massively reduce costs--not just in the tunnel costs but the model shop--and with probably little or no effect on the show from the spectators' perspective and maybe even tighten up the field.  It would sure lower the entry barriers for new teams at the least. 



#7 gruntguru

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Posted 21 October 2013 - 00:49

:up:



#8 DogEarred

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Posted 21 October 2013 - 06:57

We can come up with as many good, logical ideas as we want but expecting 11 dumbo 'Team Principals' or 'CEOs' to reach agreement on anything is asking a little too much.

The thought that some other team might have access to the same information would give them the vapours...



#9 Kalmake

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Posted 21 October 2013 - 11:15

Why not outlaw tunnel testing altogether and mandate shared open source CFD on restricted computational FLOPS?  You'd potentially massively reduce costs--not just in the tunnel costs but the model shop--and with probably little or no effect on the show from the spectators' perspective and maybe even tighten up the field.  It would sure lower the entry barriers for new teams at the least. 

Big teams have invested so much in tunnels it's unlikely they will be giving that up.

 

CFD use is restricted by flops already.

 

Virgin's car for 2010 was CFD only (maybe the other new teams too?). Nowadays Marussia uses McLaren's tunnel.



#10 JSDSKI

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Posted 21 October 2013 - 16:56

Thank you all, especially DogEarred - this has cleared up a number of things for me.  I had been thinking that the change in tyre construction had more than a straightforward mechanical effect on the performance of several teams.  I suspect that a change in deformation or even the rate of deformation has helped some and hindered others.  After all, it's not like a team can suddenly produce a new and different chassis in response to an airflow change at the front caused by a change in tire deformation.  Most teams would respond by altering bodywork and mechanical setup.  And they might hit a wall due to chassis size or shape and then simply hold on for next year.  

 

On another related question, would it be entirely illegal to run a remote control 50% or 60% car on track or skid pad?  Would that even assist in correlation?


Edited by JSDSKI, 21 October 2013 - 16:58.


#11 DogEarred

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Posted 21 October 2013 - 18:55

 

 

On another related question, would it be entirely illegal to run a remote control 50% or 60% car on track or skid pad?  Would that even assist in correlation?

 

You're welcome. Much too complicated & inconsistent I would have thought. Most likely to be entirely illegal but sounds like it could be huge fun!!!... :drunk:

 

Could be a way of making money out of some rich kids though.... :cool:



#12 bigleagueslider

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Posted 22 October 2013 - 06:23

Why not outlaw tunnel testing altogether and mandate shared open source CFD on restricted computational FLOPS?  You'd potentially massively reduce costs--not just in the tunnel costs but the model shop--and with probably little or no effect on the show from the spectators' perspective and maybe even tighten up the field.  It would sure lower the entry barriers for new teams at the least. 

I don't think a common open source CFD tool would make much difference in costs, since most teams have sponsorship arrangements for things like software.  A seat license for the best CFD application available would probably cost far less than $100K, and a first-class system to run it on would currently cost just a few hundred $K more.  The largest expense by far would be paying the salaries of qualified people to use it.



#13 desmo

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Posted 23 October 2013 - 01:32

I don't think a common open source CFD tool would make much difference in costs, since most teams have sponsorship arrangements for things like software.  A seat license for the best CFD application available would probably cost far less than $100K, and a first-class system to run it on would currently cost just a few hundred $K more.  The largest expense by far would be paying the salaries of qualified people to use it.

The point of using open/shared source CFD software wouldn't be to directly save costs but instead to cooperatively develop software that exceeds the capabilities of the current stuff for F1 development to ease the transition away from crazy expensive tunnel testing.  The development curve would steepen considerably I'd assume if everyone could see and try everyone else's hacks. 



#14 DogEarred

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Posted 23 October 2013 - 07:06

I think you are both right but only in a 'communist' sort of way. F1 teams are constantly looking for an advantage but co-operating for the common good, as proven so many times, is beyond them.

 

The idea of common open source would surely be something that universities (or even the big aircraft/defense companies) might do though.

 

Imposing yet more restrictions on this supposedly competitive sport would accelerate the current decline into adminastrative & technical mediocrity.

 

Even now, with the financial & technical restrictions that exist, does anybody know of any team just sitting back & saying 'that's enough development for now, we don't want to go over the limit, do we?'. - They will stretch & cheat the rules whatever way they can - negating any possible financial limitations. It's amazing how many graduates are employed on 'painting & decorating'...



#15 bigleagueslider

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Posted 24 October 2013 - 03:07

The point of using open/shared source CFD software wouldn't be to directly save costs but instead to cooperatively develop software that exceeds the capabilities of the current stuff for F1 development to ease the transition away from crazy expensive tunnel testing.  The development curve would steepen considerably I'd assume if everyone could see and try everyone else's hacks. 

The CFD softwares that are used by F1 teams are typically designed such that users can easily modify it for their specific applications.  They are definitely not plug-and-play softwares. In this regard commercial CFD tools are not much different than an open source CFD tool would be.  The primary difference would be that the commercial CFD softwares would be far more reliable and compatible with other engineering softwares.



#16 PayasYouRace

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Posted 24 October 2013 - 10:13

 

On another related question, would it be entirely illegal to run a remote control 50% or 60% car on track or skid pad?  Would that even assist in correlation?

 

I'd imagine it wouldn't help much. In order to get the correct force measurements you need to run at unrealistic speeds, which is where the tunnel has it's advantage. The main reason to run at a track is to see whether your developments result in laptime or handling improvements. But to do that with a scale model you'd ruin your force measurements.

 

Correlation is best done in full size car in the same or similar conditions to the tunnel. That's why the teams do straightline tests or during testing and practice you sometimes see drivers running at a constant speed down a straight.



#17 bigleagueslider

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Posted 26 October 2013 - 02:57

I'd imagine it wouldn't help much. In order to get the correct force measurements you need to run at unrealistic speeds, which is where the tunnel has it's advantage. The main reason to run at a track is to see whether your developments result in laptime or handling improvements. But to do that with a scale model you'd ruin your force measurements.

 

Correlation is best done in full size car in the same or similar conditions to the tunnel. That's why the teams do straightline tests or during testing and practice you sometimes see drivers running at a constant speed down a straight.

Actually, testing a properly instrumented 60% scale remote control car on a test track would be an excellent way of collecting data to validate/calibrate a CFD model.  On the other hand, the cost of building an accurate 60% scale remote control F1 car would likely be $1M or more.