25 replies to this topic

[zac510]

I read several years ago that when a closed wind tunnel is run at a higher pressure it simulates behaviour at a higher air speed.

While I'm not entirely sure about the science behind that or how many wind tunnels in the world can do it, the thought was triggered by reading about F1's wind tunnel testing regulations: maximum 60% model at 50m/sec.

How long until they pressurise the wind tunnel?

[phantom II]

A standard day at sea level would be, 29:92" of mercury and 56"f or 1013mb and 15'c. The indicated airspeed will equal the actual speed of the car in zero wind conditions then. Any deviation of pressure and temperature from standard will alter the indicated airspeed and it would have to be calibrated to give the true airspeed. As the pressure decreases, the indicated airspeed also decreases while the ground speed remains the same. If the pressure is above ambient, the reverse is true. The air entering the pitot tube is compared to the ambient pressure via a static vent system. By pressurizing the wind tunnel it is possible to achieve a higher indicated airspeed. Even though the true airspeed is lower, the wing and aero package will react to the indicated airspeed.
In practical terms, the downforce will be greater on a cold winter day in Monza than the middle of summer in Mexico City by as much as 30%. In other words,you would have to increase the angle of attack of the wings in Mexico to restore some of the lost downforce. Pressurized wind tunnels have been around for a long time.

Originally posted by zac510
I read several years ago that when a closed wind tunnel is run at a higher pressure it simulates behaviour at a higher air speed.

While I'm not entirely sure about the science behind that or how many wind tunnels in the world can do it, the thought was triggered by reading about F1's wind tunnel testing regulations: maximum 60% model at 50m/sec.

How long until they pressurise the wind tunnel?

[gruntguru]

Originally posted by zac510
I read several years ago that when a closed wind tunnel is run at a higher pressure it simulates behaviour at a higher air speed.

While I'm not entirely sure about the science behind that or how many wind tunnels in the world can do it, the thought was triggered by reading about F1's wind tunnel testing regulations: maximum 60% model at 50m/sec.

How long until they pressurise the wind tunnel?

There's a thing called similitude, of which I've mostly forgotten the details. Basically means you can simulate operation despite testing at lower speeds or with smaller models etc, by adjusting parameters like fluid density, viscosity etc.

[RDV]

Try water tunnels...Minardi ran models in one...talk about density...

[whatto999]

Originally posted by RDV
Try water tunnels...Minardi ran models in one...talk about density...

Think Prost mentioned tests in water tunnel at the end of 90's or beginning of 00's?

[zac510]

Do you think they are using pressurised tunnels in F1 already?

I once found a video of a water tunnel on the NASA site. It had dyes injected from the aircraft model into the water flow. I'll see if I can find it again.

edit: that was quick.. here it is: http://www.dfrc.nasa...EM-0045-01.html

[NRoshier]

mercedes currently run a water 'tunnel' on production cars to check rad/engine bay flows etc. Stated theory was that % increase in density meant % decrease in velocity.

[Fat Boy]

Originally posted by whatto999


Think Prost mentioned tests in water tunnel at the end of 90's or beginning of 00's?

Did they do aero testing at Prost?

[McGuire]

Originally posted by Fat Boy


Did they do aero testing at Prost?

maybe the shop flooded and they put a meat scale on the rope between the race car and the tow motor when they dragged it up onto dry land.

[whatto999]

Originally posted by Fat Boy


Did they do aero testing at Prost?

After some researching i can say the following.

When project started, the team were using a few years old wind tunnel located in Magny Course, where their factory (ex Ligier) was located.

The ACE wind tunnel is a rolling-road model that was purchased from Prost GP after the team folded in 2002. Originally built in 1991 for the Ligier Formula One team, it provides wind and belt speeds up to 40 m/s, and can accommodate physical models ranging from 25 percent to full scale, depending upon the vehicle. ACE uses the wind tunnel extensively for both original development of car designs and CFD verification.

About ACE:

Created in 2002 by two Formula One (ex-Prost GP) engineers AERO CONCEPT ENGINEERING provides a complete aerodynamic consultancy and development service.

Through 1998 season the old wind tunnel was enhanced a bit:

(Prost, January 26 1999) We have the windtunnel at Magny-Cours and we did a retro-fit on that tunnel throughout last year. We do have plans to build a new windtunnel here at Guyancourt and we will make the final decision in a few weeks. We have different projects under consideration but I think we will start from scratch and build a new tunnel. If we do that we will then use the two windtunnels.

They moved into new factory located in Guyancourt around February/March 1998. New wind tunnel in Guyancourt never happened as team ran out of money.
However, their wind tunnel tests expanded over time to Southampton's tunnel as reveals LinkedIn profile of
Victor de Oliveira , engineer who worked for Prost at that time (11/1998 - 12/1999) as model maker:

Working very closely with the aerodynamicists, I have worked on aerodynamic research and developments, manufacturing the 2/5 models scale AP02 and AP03 F1 for wind tunnel test. Work sessions at Magny-Cours wind tunnel and Southampton wind tunnel.

As i understand, their computer-based aero simulations at first ran on Sun's hardware platform, later on SGI's - they were Fluent's customer for the whole time.

It seems Prost GP never had serious plans for water tunnel, at least no more serious then most of other teams at that time. Story (on the internet) exists only on atlasf1 and goes back to '99. But, again, it's nothing more then "exploring the possibilities". Every (top) team did/does the same.

[LMP900]

Gurney had a water tow-tank which I was told was very good for flow visualisation.

[Fat Boy]

"Give me a few bits of wool to stick on the car, a good gust of mistral
wind, and I could come up with a better aerodynamic package on the bridge at Avignon"
- Jean Alesi on the dreadfully inefficient Prost AP02.

[Fat Boy]

Originally posted by LMP900
Gurney has a water tow-tank which I was told is very good for flow visualisation.

[LMP900]

Sorry FB - I thought they'd shut shop. Pleased to hear they haven't.

[Tony Matthews]

Originally posted by zac510
I read several years ago that when a closed wind tunnel is run at a higher pressure it simulates behaviour at a higher air speed.

While I'm not entirely sure about the science behind that or how many wind tunnels in the world can do it, the thought was triggered by reading about F1's wind tunnel testing regulations: maximum 60% model at 50m/sec.

How long until they pressurise the wind tunnel?

Zac, this is the Renault F1 windtunnel, formerly Benetton, designed to run at 1 bar over atmospheric. Whether it has ever been run pressurised I know not, but that was the design brief. Copyright TM

[zac510]

I think that was where I read it Tony.. and indeed your drawing looks familiar. It was definitely in one of the UK race engineering mags?

[Tony Matthews]

Originally posted by zac510
I think that was where I read it Tony.. and indeed your drawing looks familiar. It was definitely in one of the UK race engineering mags?

It may have been used in Racecar Engineering, Zac, and I think one Italian - Quatrorouotte(sp/) - It was done for Peter Wright's 'Formula 1 Technology' book.

[Fat Boy]

Originally posted by LMP900
Sorry FB - I thought they'd shut shop. Pleased to hear they haven't.

They're still alive a kicking. They do a lot of defense contract work, which has to be a better idea than racing cars.

[MikeTekRacing]

Originally posted by Fat Boy
"Give me a few bits of wool to stick on the car, a good gust of mistral
wind, and I could come up with a better aerodynamic package on the bridge at Avignon"
- Jean Alesi on the dreadfully inefficient Prost AP02.

i don't want to be rude to jean, but he should stick to driving and let engineering to other guys.
the AP02 was a bad car, but only fools think they could re-design it better on a piece of paper. f1 is a difficult war zone and you need a lot of stuff to make things right...just ask toyota why their car was not fast for so many years..you had the resources, the people..but not quite right

[ivanalesi]

Well, that was one of Jean's opinions on the car, the other was that a soap box had about the same downforce:)
In Competition Car Aerodynamics, the author Simon McBeath was talking about Benetton's tunnel. If I remember correctly, they never managed to make it work properly and partly B199 was done with it, of course by Nick Wurth(always forgetting how to spell his name), and the theory was that if the pressure was twice as much, it would be kind of simulating twice the speed?! I may be wrong on my memories, but it was smth to do with obtaining data for higher speeds.

[Petervl]

I would say it has to do with Reynolds similarity. In order to keep the flow 'similar' to the full scale situation the Reynolds number and Mach number should be the same for both situations.

To influence the Reynolds number without changing the scale or the velocity you need to alter the dynamic viscosity, which you can do by using another medium (water for example) or change the density. The density can be changed by by pressurizing or cooling/heating the windtunnel. (applying the gas law)

If the flows are not Reynolds similar the turbulence effects are not the same, giving different results for boundary layer development, thus false predictions of flow separation etc.

Peter

[desmo]

Originally posted by Tony Matthews


It may have been used in Racecar Engineering, Zac, and I think one Italian - Quatrorouotte(sp/) - It was done for Peter Wright's 'Formula 1 Technology' book.

Quattroruote (four wheels)

Thank you for posting that Tony, the version of the drawing in Wright's book ended up being so reduced (and in B&W) as to be essentially a waste of most of the work evident in that wonderful drawing.

[ivanalesi]

The then Benetton team, had in '98 built a wind tunnel capable of being pressurized to twice atmospheric pressure. The idea was to double the air's density and so to enable the 50% scale tunnel to generate fully realistic Reynolds Numbers at its maximum speed of 70m/s. It's understood the tunnel was never pressurized because of technical problems, but it does still offer the team a very effective wind tunnel. It is perhaps revealing that none of the other teams appear to have followed this route...

This is from the book, Peter was right:) I just remember they wanted to make it better at high speed...

[phantom II]

In testing for drag, one can make a scaled down model of the car and test it in a wind tunnel using the same Reynolds number that the actual car is subjected to. If the scale model has dimensions one 1/4 size, the flow velocity would have to be increased four times to obtain similar flow behavior.
If medium is water, drag is the focus of the test, if it is in a pressurized wind tunnel, lift is the focus of the test at F1 speeds.
As the kinematic viscosity of water is around 13 times less than that of air at 15 °C, in this case the scale model would need to be about one thirteenth the size in all dimensions to maintain the same Reynolds number, assuming the full-scale flow velocity was used.
The fluid tunnel results of Reynolds nos. on the smaller model will be similar to those of the actual car.
The higher pressure wind tunnel can be run slower to test lift for reasons that I have explained in a previous post.

Reynolds number is important in the calculation of a body's drag characteristics only. Above roughly 3×106 Re the drag coefficient drops considerably. This is F1s focus.

Originally posted by Petervl
I would say it has to do with Reynolds similarity. In order to keep the flow 'similar' to the full scale situation the Reynolds number and Mach number should be the same for both situations.

To influence the Reynolds number without changing the scale or the velocity you need to alter the dynamic viscosity, which you can do by using another medium (water for example) or change the density. The density can be changed by by pressurizing or cooling/heating the windtunnel. (applying the gas law)

If the flows are not Reynolds similar the turbulence effects are not the same, giving different results for boundary layer development, thus false predictions of flow separation etc.

Peter

[Tony Matthews]

Originally posted by ivanalesi
The then Benetton team, had in '98 built a wind tunnel capable of being pressurized to twice atmospheric pressure.

See post 15.

[Tony Matthews]

Originally posted by desmo
Thank you for posting that Tony, the version of the drawing in Wright's book ended up being so reduced (and in B&W) as to be essentially a waste of most of the work evident in that wonderful drawing.

Desmo, the use of illustrations in that book was less than perfect, there were several glaring errors... What can I say, it was out of my hands.