Ground Effect - Bring It Back

[livinglikethathuh]

bhall,
I agree with your point, but the trailing car also loses downforce by the reduction of the lift coefficient. Lift coefficient is actually dependent on the flow regime, so for example a front wing will have different Cd's for clean air (laminar flow striking the FW) and dirty air (turbulent flow striking the FW). Same applies for rear wing but with less effect, as the flow regime is already turbulent at the RW but a leading car will increase the amount of turbulence at the RW.

[rjsa]

No they´re using agressive wings because regulations allow those high cambered wings and in F1 drag is a minor problem compared to the advantages downforce provide

BTW, F1 wings are a lot more agressive (cambered) than that representation

No, they use "aggressive" wings, because that's the only way to create downforce at the sloooooooooooooow airspeeds in which F1 cars travel.

Aside from a fan car, which has its own unique set of challenges and limitations, there's no way to solve the problem of "dirty air." Given two cars running in tandem, the leading car will always, always, always displace air as it passes through the atmosphere, which means this number...

Wrong, period.

First of all, on speeds, a Cesna 180 Cruises at around 260KPH, stalls at 90KPH:



Second, about air density:

"In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric flow) refers to a flow in which the material density is constant within a fluid parcel—an infinitesimal volume that moves with the flow velocity. An equivalent statement that implies incompressibility is that the divergence of the flow velocity is zero (see the derivation below, which illustrates why these conditions are equivalent)."

Related flow constraints[edit]
In fluid dynamics, a flow is considered incompressible if the divergence of the flow velocity is zero. However, related formulations can sometimes be used, depending on the flow system being modelled. Some versions are described below:

"1 - Incompressible flow: {\nabla \cdot \mathbf u = 0} . This can assume either constant density (strict incompressible) or varying density flow. The varying density set accepts solutions involving small perturbations in density, pressure and/or temperature fields, and can allow for pressure stratification in the domain.

2- Anelastic flow: {\nabla \cdot \left(\rho_{o}\mathbf u\right) = 0} . Principally used in the field of atmospheric sciences, the anelastic constraint extends incompressible flow validity to stratified density and/or temperature as well as pressure. This allows the thermodynamic variables to relax to an 'atmospheric' base state seen in the lower atmosphere when used in the field of meteorology, for example. This condition can also be used for various astrophysical systems.

3- Low Mach-number flow / Pseudo-incompressibility: \nabla \cdot \left(\alpha \mathbf u \right) = \beta. The low Mach-number constraint can be derived from the compressible Euler equations using scale analysis of non-dimensional quantities. The restraint, like the previous in this section, allows for the removal of acoustic waves, but also allows for large perturbations in density and/or temperature. The assumption is that the flow remains within a Mach number limit (normally less than 0.3) for any solution using such a constraint to be valid. Again, in accordance with all incompressible flows the pressure deviation must be small in comparison to the pressure base state."

(emphasis mine)

Nothing happens to air density at 300KPH. Nada.

[rjsa]

How about this one? Bear in mind it has a double-diffuser.

http://i.imgur.com/rn1gY9e.jpg

http://i.imgur.com/FKy600o.jpg

I'd love to have more than random web images. it's just that when it comes to F1 aero, they're kinda hard to get, yanno?

More random images.

[bhall II]

Fair enough. I incorrectly attributed to lower density what I should have attributed to lower pressure. I was wrong.

EDIT: Oh, yeah...

First of all, on speeds, a Cesna 180 Cruises at around 260KPH, stalls at 90KPH:

And its wings also have a vastly larger surface area.

[rjsa]

Fair enough. I incorrectly attributed to lower density what I should have attributed to lower pressure. I was wrong.

EDIT: Oh, yeah...

First of all, on speeds, a Cesna 180 Cruises at around 260KPH, stalls at 90KPH:

And its wings also have a vastly larger surface area.

And 280hp. And needs 1.2t of lift to leave the ground.

Everything is interconnected, F1 isn't too slow. Neither too fast. It'just the way it is. Wings have to be small due to rules then you make them count by running an insane configuration.

[Just_a_fan]

Second, about air density:

"In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric flow) refers to a flow in which the material density is constant within a fluid parcel—an infinitesimal volume that moves with the flow velocity. An equivalent statement that implies incompressibility is that the divergence of the flow velocity is zero (see the derivation below, which illustrates why these conditions are equivalent)."

Related flow constraints[edit]
In fluid dynamics, a flow is considered incompressible if the divergence of the flow velocity is zero. However, related formulations can sometimes be used, depending on the flow system being modelled. Some versions are described below:

"1 - Incompressible flow: {\nabla \cdot \mathbf u = 0} . This can assume either constant density (strict incompressible) or varying density flow. The varying density set accepts solutions involving small perturbations in density, pressure and/or temperature fields, and can allow for pressure stratification in the domain.

2- Anelastic flow: {\nabla \cdot \left(\rho_{o}\mathbf u\right) = 0} . Principally used in the field of atmospheric sciences, the anelastic constraint extends incompressible flow validity to stratified density and/or temperature as well as pressure. This allows the thermodynamic variables to relax to an 'atmospheric' base state seen in the lower atmosphere when used in the field of meteorology, for example. This condition can also be used for various astrophysical systems.

3- Low Mach-number flow / Pseudo-incompressibility: \nabla \cdot \left(\alpha \mathbf u \right) = \beta. The low Mach-number constraint can be derived from the compressible Euler equations using scale analysis of non-dimensional quantities. The restraint, like the previous in this section, allows for the removal of acoustic waves, but also allows for large perturbations in density and/or temperature. The assumption is that the flow remains within a Mach number limit (normally less than 0.3) for any solution using such a constraint to be valid. Again, in accordance with all incompressible flows the pressure deviation must be small in comparison to the pressure base state."

(emphasis mine)

Nothing happens to air density at 300KPH. Nada.

No, those are assumptions that are used to allow a simplified modelling of the flow being studied. Air is compressible but the usual approach is to assume it's incompressible at low speeds (v < M0.3). Why? Because modelling compressibility is more difficult/time consuming to do. It's still compressible at 200mph but the effect is very small compared to other aspects of its behaviour so it's reasonable to ignore the compressibility.

Indeed, it was the assumption that air was incompressible that caused the problems for the fighter aircraft at the end of the WW2 (and in to the early work on transonic flight). They'd assumed (or just plain believed) that air behaved as an incompressible fluid - sadly, for some pilots, physics turned around a bit them by demonstrating compressibility problems in transonic regions around the control surfaces of those aircraft.

[Andres125sx]

No they´re using agressive wings because regulations allow those high cambered wings and in F1 drag is a minor problem compared to the advantages downforce provide

BTW, F1 wings are a lot more agressive (cambered) than that representation

No, they use "aggressive" wings, because that's the only way to create downforce at the sloooooooooooooow airspeeds in which F1 cars travel.

Sorry but that´s not true, not even close, and I guess you know it so not sure why are you trying to negate this

Downforce can be created by ANY airfoil, not only a high cambered wing. Airfoils use more or less camber depending on the lift/downforce needed, and max airspeed requirements, more camber means more lift/downforce, but also more drag so lower max speed. F1 use high cambered wings because they only care about downforce, drag is a minor problem so they use what create the highest downforce, high cambered wings

Actually downforce can be created even by a flat surface with an angle of attack, so you don´t even need an airfoil to create downforce

The speed wich F1 cars travel are anything but slow, for example a huge Boeing 747 and its 100 tons take off at around 230km/h, depending on the TOW (take off weight), so no the airspeed F1 cars travel are not slooooooooow as you say, they´re quite fast

Aside from a fan car, which has its own unique set of challenges and limitations, there's no way to solve the problem of "dirty air."

Maybe you didn´t read it the first 3 times I wrote it, but I´ve never said it´s posible to SOLVE dirty air problem, I´m saying it could be MINIMIZED.

Dirty air problem will always exists, I´ve said it myself in this same thread, but any problem can be bigger or smaller, depending on how do you manage it. In this case FIA management is nonexistent, as high cambered wings make dirty air problem as big as posible, so even when the problem will always exist, it could be reduced using solutions wich do not create as much dirty air as high cambered wings, and are not as sensible to dirty air, for example GE.

[rjsa]

Second, about air density:

"In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric flow) refers to a flow in which the material density is constant within a fluid parcel—an infinitesimal volume that moves with the flow velocity. An equivalent statement that implies incompressibility is that the divergence of the flow velocity is zero (see the derivation below, which illustrates why these conditions are equivalent)."

Related flow constraints[edit]
In fluid dynamics, a flow is considered incompressible if the divergence of the flow velocity is zero. However, related formulations can sometimes be used, depending on the flow system being modelled. Some versions are described below:

"1 - Incompressible flow: {\nabla \cdot \mathbf u = 0} . This can assume either constant density (strict incompressible) or varying density flow. The varying density set accepts solutions involving small perturbations in density, pressure and/or temperature fields, and can allow for pressure stratification in the domain.

2- Anelastic flow: {\nabla \cdot \left(\rho_{o}\mathbf u\right) = 0} . Principally used in the field of atmospheric sciences, the anelastic constraint extends incompressible flow validity to stratified density and/or temperature as well as pressure. This allows the thermodynamic variables to relax to an 'atmospheric' base state seen in the lower atmosphere when used in the field of meteorology, for example. This condition can also be used for various astrophysical systems.

3- Low Mach-number flow / Pseudo-incompressibility: \nabla \cdot \left(\alpha \mathbf u \right) = \beta. The low Mach-number constraint can be derived from the compressible Euler equations using scale analysis of non-dimensional quantities. The restraint, like the previous in this section, allows for the removal of acoustic waves, but also allows for large perturbations in density and/or temperature. The assumption is that the flow remains within a Mach number limit (normally less than 0.3) for any solution using such a constraint to be valid. Again, in accordance with all incompressible flows the pressure deviation must be small in comparison to the pressure base state."

(emphasis mine)

Nothing happens to air density at 300KPH. Nada.

No, those are assumptions that are used to allow a simplified modelling of the flow being studied. Air is compressible but the usual approach is to assume it's incompressible at low speeds (v < M0.3). Why? Because modelling compressibility is more difficult/time consuming to do. It's still compressible at 200mph but the effect is very small compared to other aspects of its behaviour so it's reasonable to ignore the compressibility.

Indeed, it was the assumption that air was incompressible that caused the problems for the fighter aircraft at the end of the WW2 (and in to the early work on transonic flight). They'd assumed (or just plain believed) that air behaved as an incompressible fluid - sadly, for some pilots, physics turned around a bit them by demonstrating compressibility problems in transonic regions around the control surfaces of those aircraft.

Anyway, any effect that the difference of density in the wake of a F1 car under mach .3 will make in downforce is negligible.

And that's exact the point of an assumption or approximation.

We are not talking P51s flying at mach 0.75.

[bhall II]

It was a mistake for me to bring up air density. The point I was trying to make is that the leading car in a two-car tandem arrangement will displace air as it passes through the atmosphere, which means the trailing car will have less air flow passing over, under, around, and through its aerodynamic devices. That's reduced pressure, not reduced density.

And I clearly made a mistake when I took it for granted that everyone understands and appreciates the constraints placed upon designers by rules that limit wingspans, a reality that compels the use of airfoils set at high angles of attack in order to make useful downforce at the relatively low airspeeds experienced by F1 cars.

Yes, you can absolutely reduce the effects of "dirty air" by limiting a wing's AoA, but you will also dramatically reduce downforce unless the rules are also amended to allow huge wings to make up the difference.

For example, given two otherwise identical airfoils with the following randomly-selected lift curve...



...one with no angle of attack will need a surface area that's 248% larger in order to produce the same lift force at ~200kph as a 1m^2 wing set at a 15° AoA.




EDIT: To be continued. EDIT 2: Maybe. EDIT 3: Yes!

All cars have more or less the same front wings, barge boards, floors, diffusers, rear wings, etc.



What sets the cars apart from one another is how well those components are integrated into a larger system, and it's all in the details. In other words, the best front wing isn't necessarily the one that creates the most downforce; it's the one that most seamlessly and consistently works with the rest of the car.

The problem with "dirty air" is far less about its effect on any single component in isolation; it's the deleterious effect on the interaction of those components within the system that's the real problem, and it's one that cannot be solved by simply replacing one component with another.

You will not make the car less sensitive to "dirty air" by replacing a flat floor with a pair of venturi tunnels. You will only make the floor (marginally) less sensitive to "dirty air." (And I believe it's highly doubtful the safety brigade will ever allow underbody downforce to be a car's primary source of downforce, because it's way too sensitive to ride height changes.)

This is where "dirty air" and performance differentiation converge. A trailing car will always tend to have worse aerodynamic efficiency than a car in "clean air." So, a trailing car will always tend to need a non-aerodynamic advantage in order to overtake, which the current formula doesn't allow. Hence, DRS and/or futility...

Also consider this: the rear wing was made smaller last season, and the beam wing was eliminated. According to conventional "wisdom," the resultant downforce reduction and lower wake structure should assist overtaking.



And yet...

This will always be a problem, because apparently even track modification can't help.

[rjsa]

You're missing the point here:

a) New rules.

b) Some aerodynamic devices are less sensitive to wake effects than others.

So: Let's design a new set of rules relying more on less sensitive devices.

The concept should be easy to grasp.

[bhall II]

The concept should be easy to grasp.

You would think so.

[Just_a_fan]

Anyway, any effect that the difference of density in the wake of a F1 car under mach .3 will make in downforce is negligible.

And that's exact the point of an assumption or approximation.

We are not talking P51s flying at mach 0.75.

I was just being pedantic - this is, or rather used to be, a technical forum. Some others on here may not know that assumptions and simplifications are used to make the calculations easier. They don't use these things in their fanboy threads

[Just_a_fan]

F1 use high cambered wings because they only care about downforce, drag is a minor problem so they use what create the highest downforce, high cambered wings

No, they use highly cambered wings because they have limited span available to them. The rules allow a relatively small box in which to fit the wing. In this situation, you make most downforce by making the chord as long as possible. In a restraining box, the only way to do that is to add camber. Lots of camber.

Actually downforce can be created even by a flat surface with an angle of attack, so you don´t even need an airfoil to create downforce

Yes, but the amount of downforce produced by a flat plate is not as much as a cambered wing, or rather it's not nearly as efficient. An angled flat plate will produce some quite spectacular edge vortices that will make the air behind very unpleasant.

The speed wich F1 cars travel are anything but slow, for example a huge Boeing 747 and its 100 tons take off at around 230km/h, depending on the TOW (take off weight), so no the airspeed F1 cars travel are not slooooooooow as you say, they´re quite fast

Go back and think about the respective spans and areas of the wings of F1 cars and 747s. Also, remember that F1 cars need maximum downforce in corners - the point on the track when they are at their slowest. Look at a 747 when it is at its slowest speed (that's when it's landing). What do you see? You see big multiple element flaps that create, you guessed it, a highly cambered wing. The turbulence behind a landing 747 is so bad that following aircraft are kept several miles away.

Dirty air problem will always exists, I´ve said it myself in this same thread, but any problem can be bigger or smaller, depending on how do you manage it. In this case FIA management is nonexistent, as high cambered wings make dirty air problem as big as posible, so even when the problem will always exist, it could be reduced using solutions wich do not create as much dirty air as high cambered wings, and are not as sensible to dirty air, for example GE.

Ok, how do you do it? Please note, F1 cars are already in ground effect. They don't run the cambered undersides and skirts of the classic "ground effect cars" but they still make use of ground effect. Any wing placed within its own chord length of the ground will experience "ground effect" and the closer you run it - to a point - the more the effect increases the downforce produced.

Now, you could go back to tunnels and skirts but I'm not sure how else you could implement "ground effect" and have a hope of running close together.

[Just_a_fan]

I
This is where "dirty air" and performance differentiation converge. A trailing car will always tend to have worse aerodynamic efficiency than a car in "clean air." So, a trailing car will always tend to need a non-aerodynamic advantage in order to overtake, which the current formula doesn't allow. Hence, DRS and/or futility...

The answer is, quite simply, to have active aero. Allow the car behind to adjust its wings to give it more downforce in the dirty air. This negates the effect of being close to the other car in corners and allows the driver to close up to the car ahead. Then it's down to balls, and late braking at the end of the next straight...

Alternatively, allow active suspension to return and go for more underbody downforce couple with smaller wings. This allows the car to run at the correct ride height and removes the sensitivity issue associated with "full underbody" downforce production. I'd allow the wings to still be actively adjusted as a way to trim the car when in close company with others. Indeed, it's the loss of balance that prevents the drivers from getting close, not the overall loss of downforce; when they get close they tend to get more and more understeer and this just kills the front tyres. The good drivers can deal with an overall reduction of downforce if it's done in a balanced way. Sure, it's tricky but that's what everyone wants, isn't it?

[SectorOne]

Or you know, stick a fan on it.
The concept of "dirty air" will cease to exist because the fan will simply have to do less of a job if there´s a car in front moving air out of the way for it.

No matter what conventional aero regs you come up with will always have some dirty air problems which means the car behind will have less downforce.
With a fan you can make a case for the car behind to actually have more downforce then the car in front simply because the fan on that car has to shift less air.