How accurate is our "cheap" CFD ?

[Hoffman900]

3 claims - each wrong

and .... Reynolds number similarity is big issue eg for airliner work (that's not an issue for F1)

all 3 claims 100% correct

(so-called) low-speed wind tunnels are where the real work is done
LS means 'aerodynamically-big' for high Re similarity (necessary for approach and takeoff AoAs)
this costs big money

the EU has funded noise reduction programmes for 20 years (undercarriage/'gear' noise is a big part of approach noise)
eg DNW has done a lot of this (at speeds up to 78 m/s - the noise rising with the 6th power of the velocity)

and both DNW and ONERA advertise TPS capabilities (turbofan and prop systems incorporated in the WT models)

other 'low-speed' wind tunnels are available .....

While aircraft efficiency has improved over the years, noise continues to be a problem for existing aircraft and will likely be a concern for next-generation designs. During landing, when the engines are operating at reduced power, noise from the airframe, including landing gear, can be equal to or greater than the engine noise. This visualization, from a collaboration between NASA and Boeing about airframe noise prediction, shows the simulated air flow field around the nose landing gear of a Boeing 777, representing the complex unsteady flow generated by the gear components. The visualization is colored by speed, from slower green to faster red air velocities. A strong vortex appears coming off the edge of the landing gear doors. Simulations run on NASA supercomputers at Ames allow researchers to better understand the changes in flow behavior that contribute to airframe noise.

Related: NASA is showcasing 35 of the agency’s exciting computational achievements at SC17, the international supercomputing conference, Nov. 13-16, 2016, in Denver, Colorado. To view the featured demonstrations, visit: https://nas.nasa.gov/SC17.

Image credit: NASA's Ames Research Center, Patrick Moran; NASA's Langley Research Center, Mehdi Khorrami; Exa Corporation, Ehab Fares

Last Updated: Nov. 15, 2017
Editor: Kimberly Minafra

[Just_a_fan]

once again,aviation dont care about gear aerodynamics..end

at speeds well north of a F1 car,

Why do you think all the time that speed increase complexity??????

separted flow and turbulance make complexity, not speed..

Compressible flow vs incompressible flow. An air liner must deal with both. Airliners deal with transonic / supersonic flow. That'll be an order of difficulty over the assumptions used in F1.

An airliner must be efficient and stable at transonic speeds, stable at low speeds, stable in the transit between those two regimes.

Just because aircraft need to be low drag, doesn't mean they are low complexity.

[Jolle]

at speeds well north of a F1 car,

Why do you think all the time that speed increase complexity??????

separted flow and turbulance make complexity, not speed..

Compressible flow vs incompressible flow. An air liner must deal with both. Airliners deal with transonic / supersonic flow. That'll be an order of difficulty over the assumptions used in F1.

An airliner must be efficient and stable at transonic speeds, stable at low speeds, stable in the transit between those two regimes.

Just because aircraft need to be low drag, doesn't mean they are low complexity.

Don't forget take-off and landing, aerodynamically a big challenge (with the ground approaching, angle of attack, crosswind and changing aero surfaces.

[Uwe]

Simply put, it's a case of "shît in, shît out".

Do you know who,if yes,do you agree with his opinion?
What about CFD and aeroelastic deformation ,can CFD predict and solve it?
How do you test your CFD results,with wind tunnel,do you have wind tunnel?

90% of the challenge of doing CFD is to ensure that your CAD is cleaned up as best you can, and that you have simplified geometry in a way in which is logical and allows for you to be conservative with mesh cell count in areas of low interest, and therefore use those cells in areas of higher interest.

How can I simplifed geometry, if F1 has sick complex geometry?
How do you draw F1 or any car in CAD if you dont have geometry,dimensions,yout take meter -tape and meassure car?
Meassured car like this will not represent original geometry so result will for sure incorrect..

Their goals are different, but I do concede that F1 cars produce a lot more "exciting airflow features" and so in terms of "complexity", there is definitely a lot more just going on,

That I am talking all the time.

What is you background,did you study aeronautics?
So for working at CFD and get correct results ,I must know aerodynamics science very very well?

[Jolle]

Simply put, it's a case of "shît in, shît out".

Do you know who is Peter Kampf,if yes,do you agree with his opinion?
What about CFD and aeroelastic deformation ,can CFD predict and solve it?
How do you test your CFD results,with wind tunnel,do you have wind tunnel?

90% of the challenge of doing CFD is to ensure that your CAD is cleaned up as best you can, and that you have simplified geometry in a way in which is logical and allows for you to be conservative with mesh cell count in areas of low interest, and therefore use those cells in areas of higher interest.

How can I simplifed geometry, if F1 has sick complex geometry?
How do you draw F1 or any car in CAD if you dont have geometry,dimensions,yout take meter -tape and meassure car?
Meassured car like this will not represent original geometry so result will for sure incorrect..

Their goals are different, but I do concede that F1 cars produce a lot more "exciting airflow features" and so in terms of "complexity", there is definitely a lot more just going on,

That I am talking all the time.

What is you background,did you study aeronautics?
So for working at CFD and get correct results ,I must know aerodynamics science very very well?

For F1 cars in CAD, that works the other way round, they design in CAD and construct from there (trough printing, CNC or other methods). As for already exciting objects: 3D scanning, measure it with a scanning tool or replicate it “on sight” of course.

[Billzilla]

Where do you see aerodynamics influence at gear?not even airfoil shape anywhere!
Totaly negleceted in aerodanynamics sense!

https://insights.globalspec.com/images/ ... ype-hl.png

Hoffman 900 beat me to it, but the main concern with the aerodynamics for airliner landing gear is to reduce the noise it makes when extended. Not a significant factor on take-off & departure as the gear is typically selected up a few seconds after leaving the runway, but more so on approach & landing as the engines are idling (or close to it) hence the gear noise is proportionally more significant.
The various lift-increasing devices, such as Kruger flaps, slats, trailing-edge flaps, etc, also are developed to reduce noise as much as is reasonable.

Yes airliners do go through extensive CFD before metal is cut, but also quite a lot of wind tunnel time as well.

[Dynamicflow]

When you see a landing gear simulation for aircrafts they are generally done for wind noise purposes - lets just say aero''acoustics'' is a lot more difficult to get your head around than aero''dynamics'' in this instance. You really have to understand what the flow is doing and steady state CFD will not cut it, it has to be run in transient so you can resolve all the frequencies of interest between 50Hz and 10,000Hz on the noise spectrum. This spectrum is made up of three dominant noise sources, Monopoles, Dipoles and Quadrupoles. In simple terms, Dipole sources are noise generated through the stagnation pressure and changes in that pressure due to changes in up stream turbulence intensity, Quadrupoles are noise sources due to pressure fluctuations in the turbulent wake region both away from surfaces and surfaces in contact with the turbulent flow. Lets ignore monopoles for now, it deals mostly with how the cabin is sealed to avoid noise getting through via leakage, etc.

The reason landing gears are such a challenge is that for measuring forces you can run scale models in the wind tunnel, match the Reynolds number and you pretty much get good numbers where as when it comes to aero-acoustic testing scale testing cannot be done since you cannot scale the speed of sound unless you change the properties of the medium (good luck with doing that!), hence it has to be done full scale.

[Uwe]

Big boss has entered the chat

How do you know geometry for F1 2021 car?
If you dont have real dimensions like teams have ,resluts cant be correct?

So isnt just CFD problem,first step is to draw car like original,but this is not so easy...?

[jjn9128]

How do you know geometry for F1 2021 car?
If you dont have real dimensions like teams have ,resluts cant be correct?

So isnt just CFD problem,first step is to draw car like original,but this is not so easy...?

I don't understand the question, the rules are put online so anyone can download and produce a car?! You're doing something for a road car right? You could maybe think of getting it laser scanned.

[Uwe]

How do you know geometry for F1 2021 car?
If you dont have real dimensions like teams have ,resluts cant be correct?

So isnt just CFD problem,first step is to draw car like original,but this is not so easy...?

I don't understand the question, the rules are put online so anyone can download and produce a car?! You're doing something for a road car right? You could maybe think of getting it laser scanned.

Can you post this online rules?

Yes doing road car for race track and lookig for best solution for underside,goal is get max downforce because no tehnical regulation at aerodynamic of car..
How much cost laser ?
But this option is not good for me because I dont know how to work with CFD and dont have PC power to solve this...
So for me is better option real data meassurment,with static ports,pitot tube,load cell etc..

[jjn9128]

Can you post this online rules?

https://www.fia.com/regulations

[Uwe]

Can you post this online rules?

https://www.fia.com/regulations

Hmm 152 papers!
How many months you need to drawn car for topic "CFD for 2021 F1 car" ,you make drawing?
auto CAD or catia?

This car exist only in your drawings so CFD results from this topic cant be checked?

[jjn9128]

Hmm 152 papers!
How many months you need to drawn car for topic "CFD for 2021 F1 car" ,you make drawing?
auto CAD or catia?

This car exist only in your drawings so CFD results from this topic cant be checked?

Only took a few days to get the working cad model.

We're always very upfront that we're just 2 guys (albeit well educated, incredibly intelligent, roguishly good-looking, sexually virile...) working in our free time not a team of 60-100 aerodynamicists going full time.

[Zynerji]

Hmm 152 papers!
How many months you need to drawn car for topic "CFD for 2021 F1 car" ,you make drawing?
auto CAD or catia?

This car exist only in your drawings so CFD results from this topic cant be checked?

Only took a few days to get the working cad model.

We're always very upfront that we're just 2 guys (albeit well educated, incredibly intelligent, roguishly good-looking, sexually virile...) working in our free time not a team of 60-100 aerodynamicists going full time.

[Uwe]

We're always very upfront that we're just 2 guys (albeit well educated, incredibly intelligent, roguishly good-looking, sexually virile...) working in our free time not a team of 60-100 aerodynamicists going full time.

so you are TOO DAMN PRETTY?

how CFD deal with aeroelesticty,at 320km/h when front wing bend,twist etc
can software predict this and solve it?