10 replies to this topic

[amardeep]

The topic more or less says it all, how do you calibrate a wind tunnel ? What do you do, and what are you trying to avoid ?

[swaction]

AND..

Why can't teams with the brain power of NASA calibrate one?

[rhm]

What you should do is buy this book, read it and report back

http://www.amazon.co...uct/0471557749/

It's been on my amazon list of things to buy for ages. Maybe one day...

[macoran]

Can we go one step backwards ?

Who designs the windtunnels ?
I mean, every F1 team tunnel seems to be different, and I cannot imagine "Windtunnel Co Ltd" issuing a brochure and pricelist. (Sales target per annum springs to mind).

The teams I presume design them in house and have major components ordered and made to spec.

[rhm]

Actually, there are consultancies that design wind tunnels for teams. There are two aspects to the tunnel: (a) the tunnel itself including the fan and flow-conditioning equipment and (b) the ballance (that takes the force measurements) and the boundary layer management (including rolling road, suction and blowing equipment, etc). The consultants will come up with a design for the tunnel itself and that will usually be constructed by a seperate engineering firm. Then there is the equipment (b), all of which is made to order, but may be available to standard designs from specialist suppliers or made to order.

There is at least one team in F1 that has a tunnel that is a copy of another team's because they used the same design consultancy and to keep the lead-time down just said "give us what you did for them". I don't have time to find the article now, but it'll be in the autosport.com archive somewhere. Normally though, each tunnel is an improvement on the last one in some way.

[no-clue]

Assuming it's constructed, then the calibration process involves some of the following:
- verifying the turbulence of the flow (or the lack thereof) and adjusting meshes and grids to help achieve the desired level
- setting a boundary layer profile, typically 2mm off the belt, freestream velocity of 100%
- making sure belt and wind speed are matched, typically to less than 0.1 metre / sec
- calibrating fan speed so that there are on pulses in the tunnel velocity
- using known accurate weights and measures to validate load cell readings, may they be overhead balances, wheel drag load cells, under floor load cells, etc.
- any mechanical movements will be checked for absolute displacements and any corrections built in due to model weight / aero loads
- if there is a tunnel cooling system, then making sure that the air temperature & humidity remains within set tolerances
- regular in-house coffee machine calibration. Usually takes longer than windtunnel calibration.

[Hellenic tifosi]

It may not be directly related to the topic title, but I think that the common excuse of "a mistake in wind-tunnel calibration" is used many times in order to cover some fundamental design flaws. PR rules the world these days it is much easier to attribute a failure to a mis-calibration than to simple incompetence.

[Ray Bell]

You might ask condor about these things...

She's seen a wind tunnel or two.

[rhm]

Originally posted by no-clue
Assuming it's constructed, then the calibration process involves some of the following:
- verifying the turbulence of the flow (or the lack thereof) and adjusting meshes and grids to help achieve the desired level
- setting a boundary layer profile, typically 2mm off the belt, freestream velocity of 100%
- making sure belt and wind speed are matched, typically to less than 0.1 metre / sec
- calibrating fan speed so that there are on pulses in the tunnel velocity
- using known accurate weights and measures to validate load cell readings, may they be overhead balances, wheel drag load cells, under floor load cells, etc.
- any mechanical movements will be checked for absolute displacements and any corrections built in due to model weight / aero loads
- if there is a tunnel cooling system, then making sure that the air temperature & humidity remains within set tolerances
- regular in-house coffee machine calibration. Usually takes longer than windtunnel calibration.

Hey, nice input. You should post here more often. Then you'd lose the "new member" flag as well.

[amardeep]

- verifying the turbulence of the flow (or the lack thereof) and adjusting meshes and grids to help achieve the desired level
- setting a boundary layer profile, typically 2mm off the belt, freestream velocity of 100%

Could you explain what these mean a bit more ?

I don't know what "meshes and grids" refers to, are these part of the physical structure of a typical windtunnel ?

I know the boundary layer refers to the flow over a surface, and that the flow velocity is zero at the surface, increasing the further you get away from it. Are you saying that typically you'd expect the velocity to be equal to that unaffected by the surface (i.e. freestream) when 2mm away from the belt that simulates the moving road under the car ? Does the tunnel and/or the operation of it get modified to achieve this goal (and why would you want to prescribe this particular 2mm distance anyway) ?

Sorry if I have misunderstood, as you may have guessed, I don't know a lot about wind tunnels :-)

[condor]

Meshes and grids are usually referring to theoretical work but assume for practical aero purposes would be flow straightening screens - pic here is of a continuous flow wind tunnel where I used to work. In this case a honeycomb is being used as the flow smoother ( and as it name implies is similar in construction to honey bees.)
What isn't mentioned on the diagram is that there are turning vanes at the corners - these curved vanes smooth the air round the corners and also have mesh screens ( though I thought their primary use was to trap any piece of loose model - sometimes a bit of plaster or wax covering a sunken screw would come loose)

http://www.ara.co.uk...cuitdiagram.jpg