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Wind Tunnel Testing


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#1 blueprint2002

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Posted 20 July 2020 - 05:31

Some years ago, Peter Wright wrote an article (maybe for Racecar Engineering) in which he described in some detail, and with the clarity so typical of him, the instrumentation used in the wind tunnel testing of F1 cars. Drag and down forces are naturally measured, among other parameters.

He also mentioned that, as seems logical, compressed air is piped to the model exhaust tailpipes, to simulate the flow of exhaust gases, which have a considerable influence, as is widely known.

I have been wondering how the drag of the radiators and oil coolers is simulated, as the flow from the exits, near the rear of the car, must obviously be affected by this, in turn affecting the total flow pattern. Such simulation must naturally be based on values already known, or estimated, for these items, as installed in ducts similar in shape and size to those intended for the car. Anyone have any knowledge of this matter?

 



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#2 DogEarred

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Posted 20 July 2020 - 11:36

I've heard of attempts to heat the exhaust air also. It makes a small difference but obviously but I'm not sure it's used at all as heating it to representative temperatures is difficult and dangerous.

 

Radiator cores can be modeled with reasonable accuracy using stereo lithography. (3D printing) - They don't need to contain fluids

 

Pressure tappings can be built in to components in order to take readings & confirm (or not) CFD predictions.

 

Many aerodynamic components on the wind tunnel models have multiple pressure tappings incorporated.



#3 gruntguru

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Posted 20 July 2020 - 21:52

I would think the radiator ducting would need some assistance also - either added air or heating elements. The exiting air has a greater volumetric flow due to the added heat. The ducting itself would be designed to generate "thrust" in the same way a jet engine generates thrust.



#4 blueprint2002

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Posted 21 July 2020 - 01:31

I've heard of attempts to heat the exhaust air also. It makes a small difference but obviously but I'm not sure it's used at all as heating it to representative temperatures is difficult and dangerous.

 

Radiator cores can be modeled with reasonable accuracy using stereo lithography. (3D printing) - They don't need to contain fluids

 

Pressure tappings can be built in to components in order to take readings & confirm (or not) CFD predictions.

 

Many aerodynamic components on the wind tunnel models have multiple pressure tappings incorporated.

 

 

I would think the radiator ducting would need some assistance also - either added air or heating elements. The exiting air has a greater volumetric flow due to the added heat. The ducting itself would be designed to generate "thrust" in the same way a jet engine generates thrust.

 

Any idea what the air temperature after the radiator and after the oil cooler would be?

The exhaust temperature could be 400C or even higher: reproducing this in the tunnel might indeed be dangerous, though it would certainly add to the accuracy of the results.



#5 gruntguru

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Posted 21 July 2020 - 01:47

No idea. Definitely somewhere between ambient and coolant temperature and certainly significantly lower than coolant temperature. A reasonable estimate could be obtained if the cross sectional area of the ducting and the heat rejection in kW could be estimated. The assumption would be that the air velocity through the duct is similar to the car's velocity. For example:

Duct cross section = 0.2 m^2

Velocity = 50 ms^-1

Heat rejection = 300 kW

This gives massflow (mdot = rho x V x A) = 1.2 x 50 x 0.2 = 12 kg/s

delta T = heat/(mdot x Cp) =300/(12 x 1.005) = 25*C

 

So if ambient temperature is 30*C, the outlet temperature will be 30+25 = 55*C

Anyone with better numbers on duct area etc, please recalculate.



#6 Greg Locock

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Posted 21 July 2020 - 02:59

Somewhat o/t the P-51 used thrust from the radiator. 



#7 Charles E Taylor

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Posted 21 July 2020 - 09:18

Hi

 

 

You might find this interesting.

 

https://core.ac.uk/d...df/77602529.pdf

 

 

 

I have often wondered why designers have not made more use of exhaust augmentation for reducing cooling drag. (Now not allowed in F1)

 

https://ntrs.nasa.go...19930091895.pdf

 

 

 

For the original Meredith Effect paper.

 

http://naca.central....arc/rm/1683.pdf

 

 

 

 

Have fun.

 

 

 

 

 

Charlie

 

 

 

 

 

 

 



#8 DogEarred

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Posted 22 July 2020 - 12:07

Some great reading there, to make a change from my usual 'Beano' comic.   :clap:

 

Just shows the power of CFD analysis these days.

 

Another complex area not yet mentioned are brake ducts of course. With brake discs reaching temperatures in the 1000C region & very complex ducting, hub & wheel geometry,

CFD is the only real tool to use. 



#9 desmo

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Posted 22 July 2020 - 14:43

Wright specifically mentions in his now ancient "F1 Technology" book that that airflows within the sidepods and exhaust flows are indeed included in the physical wind tunnel models. I'm operating from memory here, I'll dig out the book if needed.



#10 blueprint2002

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Posted 23 July 2020 - 03:27

No idea. Definitely somewhere between ambient and......

 

 

Somewhat o/t the P-51 used thrust from the radiator. 

 

 

Hi

 

 

You might find this interesting......

 

 

Some great reading there, to make a change......

 

Wright specifically mentions .....

 

Thanks all for your valuable contributions. Plenty to read and to think about, all useful for closing my personal "aerodynamic gap".

:)  :)  :)