What differentiates high/low speed downforce?

[raymondu999]

Hey all. Just wondering on this point as it seemed last year the RB5 (initially, at least) was lacking-ish in low-speed downforce but great in high speed. It thrived on the fast flowing tracks such as silverstone, suzuka, or interlagos, all downforce-heavy tracks. But then come places such as Monaco, and they don't quite have the same way. Also Button said a while back that they have good high-speed downforce, but not good in the low-speed downforce sections. What actually differentiates the downforce types? Thanks

[Ogami musashi]

Those quotes need to be taken in their full context.

Downforce is a parabolic function of speed, that is, it increases with the square of speed and for racing cars, physical effects that mitigate that curve are almost negligible.

Thus, if you have more downforce that the others in high speed corners, you'll have more in low speed corners too.

What can change that are mechanical aspects of the car, ride height, attitude due to suspension, centering etc, or possible tolerance of wings to yaw angles but from a pure fluids physics perspective, there's one parabolic curve and she doesn't deform.

The other parameter possible, between tracks, is that team bring different packages (but that very rare now) for wings and maybe some could not opt for more aggressive downforce profiles because they had better efficiency (downforce/drag ratio)..

But taken like that, their quotes mean nothing;

[Belatti]

Im no aerodynamicist but I will agree with you Ogami.

A single air particle in its way form the front to the rear of the car, has to travel arround many "aero" car arts that disturbs its way. I think that the whole design of the car can make that while speed increases, some of those car aero parts sends those particles to somewhere that decreases -or not- the efficiency of the aero part that is a bit rearward.

Its a system connected in a series, if you will. So it can happen that a system -a car- can work perfectly at 150kph and then have disrruptions that decreases its DF at 250kph to -maybe- recover at 300kph. I think that that may happen to boundary layers braking here and there.

A good example is some touring cars I have worke with, where a car shape that could not be changed, had a larg DF drop between 170kph and 200, to regain a lot of DF beyond 210kph...

[autogyro]

You are right Belatti, there are countless reasons for possible changes in DF from low to high speed and it is very useful to drive the cars to experience it rather than just rely on the math.

[raymondu999]

Hey all. Just a question here. I've heard many people say that at high speed, "aero takes over." Is this because at low speed there's just a negligible amount of aero grip anyways? Also, wouldn't the grip not just be aero vs mechanical, but more of mechanical x aero grip? As in, more mechanical grip would also benefit them in the high speed, more aero would also benefit them in the low speed, to an extent? Finally, say that the car had 0 lift, 0 downforce. But it had a HUGE amount of mechanical grip (comparable to what they have nowadays in aero and mechanical grip. Would that mean that they would be able to take the high speed corners with the same speeds, or do they REALLY need aero grip for that? (Barring issues such as the car toppling over of course)

[Ogami musashi]

Im no aerodynamicist but I will agree with you Ogami.

A single air particle in its way form the front to the rear of the car, has to travel arround many "aero" car arts that disturbs its way. I think that the whole design of the car can make that while speed increases, some of those car aero parts sends those particles to somewhere that decreases -or not- the efficiency of the aero part that is a bit rearward.

Its a system connected in a series, if you will. So it can happen that a system -a car- can work perfectly at 150kph and then have disrruptions that decreases its DF at 250kph to -maybe- recover at 300kph. I think that that may happen to boundary layers braking here and there.

A good example is some touring cars I have worke with, where a car shape that could not be changed, had a larg DF drop between 170kph and 200, to regain a lot of DF beyond 210kph...

Hello,

What mainly changes the curve are non linear Aerodynamics due to the parameters changes i quoted : Ride height and attitude changes speed bumps and yaw specifications (over and understeering).

The fluids mechanics in themselves do not change their behavior along speed for race cars speeds.

[Belatti]

Sorry, when I wrote "but I will agree with you Ogami" I meant "but I will not agree with you Ogami"

The fluids mechanics in themselves do not change their behavior along speed for race cars speeds.

What I IMHO get from this statement is that its wrong. Of course the behavior changes... Isnt a wing stalling or a boundary layer separation point shifting a behavior change?

As far as I can see, aerodynamics is like in any other system you engineer: a number of elements working together that has relatives dependances on each other. When there are elements that works in series, like in a chain you know what a faulty link would do to that system.

And there is nothing parabolic in that.

[Belatti]

And remember:

- An engineer thinks his equations come close to reality.

- A physicist thinks that reality come close to his equations.

Both are wrong

[Ogami musashi]

Sorry, when I wrote "but I will agree with you Ogami" I meant "but I will not agree with you Ogami"

The fluids mechanics in themselves do not change their behavior along speed for race cars speeds.

What I IMHO get from this statement is that its wrong. Of course the behavior changes... Isnt a wing stalling or a boundary layer separation point shifting a behavior change?

As far as I can see, aerodynamics is like in any other system you engineer: a number of elements working together that has relatives dependances on each other. When there are elements that works in series, like in a chain you know what a faulty link would do to that system.

And there is nothing parabolic in that.

No no, what i meant is that downforce (the phenomenon) doesn't change with speed for race car speeds.

That is, if you're car had a constant ride height and attitude the downforce curve would follow the parabolic.
Because speed has nothing to see (for race car speeds, compressibility and heat transferts effect are another topic for planes) with stall or whatever you want.

The proof of that is that in race car engineering you use aero maps that are downfroce vs...ride height(for each location).

That is fluids physics and there's no such thing as theory opposed to facts;

What i said next is that because mechanical changes occur with speed, the downforce plot is not parabolic.


Thus i wanted to stress that while you experience downforce changes with speed (compared to the parabolic curve) the aerodynamic effect in itself doesn't changes behavior with speed until you change something mechanical.

So, from my first post..i don't see where we disagree in fact.

[autogyro]

IMO the problem is that you confuse the meanings of fact and truth, which is a common mistake made by many inteligent engineers, scientists and students.
A fact is a transient concept within human understanding, it can be changed or completely negated by other later (in time) facts.
A fact should only be used as a scientific base for theory and development, not worshiped as aerodynamics and DF is by some people at the expense of understanding and progress. That way leeds to the end of F1 in this context.

Truth is a subjective and far more important thing that sometimes takes a life time to find.
It is advisable for you to look for another religion IMO.

[Ogami musashi]

That's completely irrelevant to the topic and a continuity of your personal attacks since several posts.

the FACTS (that we can see) are that for a given airfoil at a given AOA and into the racecars typical speeds there's NO changes of behavior (no stall,no turbulence development or whatsoever) due to increase in speed.

The other fact is that aero maps show differences in downforce with ride height changes as well as AOA changes (attitude of the car that changes the AOA of the wing)

The correlation between the two is simple: With speed, reactions of the car (mechanical) are different (ride height and AOA), thus aerodynamics change, which in turn changes downforce.


There's no such thing with truth, theory,practice, myth or whatever you want, those are facts that anybody with enough knowledge to interpret them can see, be it an engineer, a driver, a donkey or anything else.

[Mystery Steve]

... for a given airfoil at a given AOA and into the racecars typical speeds there's NO changes of behavior (no stall,no turbulence development or whatsoever) due to increase in speed ...

Typically, lift and drag coefficients (C_L and C_D) are a function of Reynold's number, so even individual components can be affected by velocity as the flow can separate, vorticity can occur, etc. Depending on the component, this effect can be dramatic or barely noticeable. It's not necessarily a black/white thing.

You are correct in coupling the aerodynamic and mechanical effects, though. When you design a car, you're really designing a system of components and a systemic design approach needs to be taken... everything is connected to everything.

[autogyro]

That's completely irrelevant to the topic and a continuity of your personal attacks since several posts.

the FACTS (that we can see) are that for a given airfoil at a given AOA and into the racecars typical speeds there's NO changes of behavior (no stall,no turbulence development or whatsoever) due to increase in speed.

The other fact is that aero maps show differences in downforce with ride height changes as well as AOA changes (attitude of the car that changes the AOA of the wing)

The correlation between the two is simple: With speed, reactions of the car (mechanical) are different (ride height and AOA), thus aerodynamics change, which in turn changes downforce.


There's no such thing with truth, theory,practice, myth or whatever you want, those are facts that anybody with enough knowledge to interpret them can see, be it an engineer, a driver, a donkey or anything else.

Sorry but it is impossible to converse with someone who believes that aerodynamics is the prime religion, not only for humans but for all forms of life.
Unfortunately it shows the dismal state F1 has descended to.

[Ogami musashi]

Sorry but it is impossible to converse with someone who believes that aerodynamics is the prime religion, not only for humans but for all forms of life.
Unfortunately it shows the dismal state F1 has descended to.

???? I seriously think you should calm down and think about what you write..

... for a given airfoil at a given AOA and into the racecars typical speeds there's NO changes of behavior (no stall,no turbulence development or whatsoever) due to increase in speed ...

Typically, lift and drag coefficients (C_L and C_D) are a function of Reynold's number, so even individual components can be affected by velocity as the flow can separate, vorticity can occur, etc. Depending on the component, this effect can be dramatic or barely noticeable. It's not necessarily a black/white thing.

I totally agree, but race car speeds (and sizes) do not imply big changes in flow behaviors due to speed.

Reynolds numbers in standard conditions for race cars are quite below the 5x10^5 values and cornering speeds barely vary from simple to double. So the dominant factor for transition is by far Angle of Attack.

Now you're right it is not black or white.

[Mystery Steve]

Sorry but it is impossible to converse with someone who believes that aerodynamics is the prime religion, not only for humans but for all forms of life.
Unfortunately it shows the dismal state F1 has descended to.

Birds seem to enjoy it...

I don't see where he claimed aerodynamics to be the holy grail. Maybe I missed it?