Wind tunnel talk 2012

[n smikle]

Essentially too big a model makes the tunnel behave like a tunnel instead of the sky?

[Crucial_Xtreme]

This faith in a 100% tunnel is not well founded.

Using a 100% wind tunnel to test a F1 car could have as many accuracy issues as testing with a 60% model. There are simply no 100% tunnels big enough to do testing without blockage issues. Note the effect on the model when tested in the two sizes of test chambers.

Brian

No you're trying to make bloackage more of an issue than it really is. The blockage (ratio of model frontal-area to test-section-area) shouldn’t exceed 7.5%. Once the teams are aware of the frontal area of their car, test section area and scale (50%, 60%, 100%), one now can calculate the blockage in percentage for the scaled vehicle.

Again, there is a reason why Lotus gave up 4 days of 60% testing for one day of 100%. I'm sure they have any bloackage concerns under control.

[quidam]

It's not 4 days of 60% testing but 4 days straight line (100km) testing.

[hardingfv32]

The blockage (ratio of model frontal-area to test-section-area) shouldn’t exceed 7.5%. Once the teams are aware of the frontal area of their car, test section area and scale (50%, 60%, 100%), one now can calculate the blockage in percentage for the scaled vehicle.

1) Not easy to find info. Where did you get the 7.5% blockage number?

2) Would you say that the front and rear wing flows make the car bigger than what the normal frontal area might specify?

3) Can't find much data on the Windshear test chamber area. They say the nozzle is 10' tall X 18' wide. Does the 7.5% number apply to the nozzle or the main volume of the chamber?

4) The Windshear unit is a 3/4 open jet test section. Does that mean the nozzle is 3/4 the size of the test section cross section?

Brian

[marcush.]

maybe it´s time for the mods to move the tunnel related posts to the proper thread?


anyways:

tunnel calibration and benchmarking includes moving the outer walls of the test section to optimise the model behaviour and match it to real world .....so it´s iterative ,experimental...not a claculation thing ..

A 60% model is a BIG item already - the comparison above is not really representing the change of blockage when going full scale.

My thought on this : you could integrate the model shop work into the work needed to produce the real thing....all moulds could be reused for example to produce the end product .the sclae models basically create :extra design work -press the 60% button? you need SUPER accurate molds and parts to test ...etc etc ..when you could produce one extra tub to accomodate the test equipment for aero work ..

[MIKEY_!]

Brian:
2) the upwash from the rear wing will interact with the roof of the chamber more than (for example) a neutral aerofoil of the same frontal area.

marcush, you are right we need a new thread for this, post self-reported, mods do your thing...

[Lycoming]

Katz (in Race Car Aerodynamics: Designing for Speed) cites 7% as the maximum ratio of frontal area to test section area to not be affected by the boundary layer on the walls.

The point of 100% scale is to test in a tunnel that gets you that ratio with a full scale model. And tunnels like that definitely exist.

[Crucial_Xtreme]

1) Not easy to find info. Where did you get the 7.5% blockage number?



Brian

I've seen 7.5% & 10% of frontal area cited. My only point was I'm sure the tunnel operators at WindShear are aware of blockage and have plans in place to make it a non-factor when obtaining data.

http://engineering.sdsu.edu/~hev/aerodyn.html <-- 7.5%

http://www.symscape.com/blog/wind-tunnels-and-cfd <-- 10%

[hardingfv32]

My only point was I'm sure the tunnel operators at WindShear are aware of blockage and have plans in place to make it a non-factor when obtaining data.

And the 60% tunnel operators have plans to correct their scale issues. Both types of tunnels use correction techniques, so there is an equal chance of errors being introduced.

Brian

[hardingfv32]

My thought on this : you could integrate the model shop work into the work needed to produce the real thing....all moulds could be reused for example to produce the end product .the sclae models basically create :extra design work -press the 60% button? you need SUPER accurate molds and parts to test ...etc etc ..when you could produce one extra tub to accomodate the test equipment for aero work ..

I question the easy of testing with a real car. The control structure has to be more robust and this would be more intrusive.

There might not be a requirement for the same accuracy in the actual car body parts verses the accuracy of the wind tunnel body parts. There could be a different cost benefit model used on the actual cars. I am not sure of the issue surround body part accuracy.

Brian

[marcush.]

http://www.mulsannescorner.com/bentleyelleray.html

taken from mulsannescorner .com

very interesting read about tunnel and real world correlation etc...

[marcush.]

as we are back to the tunnel discussion with MGP now having 60%model size.
I had thought Honda err MGPs tunnel had 100% capability allready as they introduced their new tunnel in 2006? Interestingly
enough the phasing in of this tunnel correlates to the fall from grace of Honda .....may it be this tunnel was not trusted and the team kept the 50% modelsize to be able to correlate to their trusted old unit -which is ´now no longer available (rented by HRT) as you canonly use one Tunnel anyways....

[strad]

Thanks marcush....Interesting read..

[marcush.]

so come on guys no input here ?

MGP has just made the step to 60 % in the midst of the 2012 season.Why would you do that ? They did not have to build a new tunnel for this as their tunnel is made for full scale testing since 2006...very mysterious .

how is the exhaust system integrated into the model and how is the heat removed from the system again as it would be a
big factor to the windtunnel having the exhaust gas heating up the tunnel air in no time...do they have a big aircon or what?

[strad]

Hmmmm maybe a dumb statement,,,wouldn't be my first,,,I thought the air temp was constant at a set humidity and density .