Formula 1 Aerodynamics - article series and general discussion

[Just_a_fan]

I suspect that there is a good deal to be gained in this discussion by agreeing on some common terminology. As an example I don’t think that @JAW and @Godlameroso mean the same thing by “choke”.

Perhaps using technical definitions rather than hand-waving made-up stuff would be helpful. It's how engineering works, really.

[godlameroso]

Pictures are worth 1,000 words. Turbulence isn't bad, vortices are turbulent flows that can be laminar. And they have a soft chewy low pressure center.

Expressing this relationship in mathematical terms is difficult for dumb people like myself. It is beyond the realm of my capacities, but some of you are exceptional when it comes to that, perhaps with enough analogies and points of reference, we can agree on some common points and the smart among us can translate this into a formula. As it stands I can only use analogies to convey my ideas.

Look closely, the plane has the wings splayed outwards, the under side of the plane is the static pressure side, you can see how all the air wants to wrap around the bottom of the plane. The contrails get pulled to the center of the plane because all the airflow above the plane is slick fast moving air. The still static high pressure air gets pulled in the direction of lowest pressure.

It doesn't matter if it's turbulent or laminar. Turbulent air is just air trying to fill a void, void within voids.

[godlameroso]

The reason tire squirt chokes the diffuser is because turbulent flow mixes really well. If the tire squirt is strong on the inboard side of the tire, it will either go to the back of the tire, or into the diffuser throat. Since it is turbulent air it fills the low pressure center of the diffuser and "chokes" it.

Reduce tire squirt by reducing pressure difference between front and rear of the tire, lowers the probability of the tire squirt choking the diffuser.

Alternatively, you can use strong vortices to both help accelerate air, and provide a high pressure barrier for the tire squirt, which will fill the vortices instead of the low at the center of the diffuser.

But why just settle for one approach when you can combine several and increase the performance of the diffuser, along with the rear wing in one fell swoop?

Since the diffuser vortices combine with the rear wing vortices, strengthen the rear wing vortices to strengthen the diffuser vortices, which will create more laminar divergent flow for a greater low pressure at the center of the diffuser, which creates a faster path for air upstream of the diffuser to pass through. That's why you have a cape, and why the leading edge of the floor all nice and raised up, so you have a good supply of air to accelerate under the car.

Red Bull, Alpine, and McLaren have shown you don't need a barn door rear wing to strengthen the rear wing tip vortex, the retraction and slots, and curvature of the wing can help.



Honestly the rear wing is excellent preparation for 2022 as this 2022 rear wing does almost exactly what I'm talking about.

[jjn9128]

This is the problem with making fun of people for having education. But then misusing terms which just serves to confuse issues. Tyre squirt doesn't choke the diffuser. A "choked" duct would be one where the mass flow exceeds the capacity of the area so the flow stalls (boundary layer separates). The issue of tyre squirt is mainly one of dynamic pressure. So "low energy" flow going into a "high energy" region. Not that it has owt to do with energy.

Tyre squirt is about the rotating boundary layer meeting the immovable object of the ground so rolling up. Then jetting around the tyre sidewall. So there's not a let you can do to influence the squirt vortex. But instead try to influence where it goes.

I'm not sure any "real" 2022 rear wings will have that profile.

[Just_a_fan]

Red Bull, Alpine, and McLaren have shown you don't need a barn door rear wing to strengthen the rear wing tip vortex, the retraction and slots, and curvature of the wing can help.

The barn door wing isn't about the wing's tips or its endplates. It's about the rear wheel aerodynamic devices laughingly considered to be part of the brake duct. The three you mention are less hampered by the rules that reduced these devices. Mercedes runs the big rear wing because the rule about the brake duct devices has hampered them resulting in less diffuser throat down force. So they are forced to run a bigger rear wing to compensate.

[Just_a_fan]

https://files.catbox.moe/r3fg62.jpg


Look closely, the plane has the wings splayed outwards, the under side of the plane is the static pressure side, you can see how all the air wants to wrap around the bottom of the plane. The contrails get pulled to the center of the plane because all the airflow above the plane is slick fast moving air. The still static high pressure air gets pulled in the direction of lowest pressure.

The contrails aren't being pulled to the centre of the plane at all. They're streaming from the wing tips in basically a straight line.

The airflow over much of the aircraft is turbulent. The leading edges of the wings is laminar, as you go back it becomes turbulent. There's a big pile of condensation "above" the aircraft because the whole is acting as a lifting body thanks to its dimensions and the angle of attack. It was designed this way - which is why an F15 was able to fly and land with one wing torn off. There's as much Newton as Bernoulli in that image.

[godlameroso]

This is the problem with making fun of people for having education. But then misusing terms which just serves to confuse issues. Tyre squirt doesn't choke the diffuser. A "choked" duct would be one where the mass flow exceeds the capacity of the area so the flow stalls (boundary layer separates). The issue of tyre squirt is mainly one of dynamic pressure. So "low energy" flow going into a "high energy" region. Not that it has owt to do with energy.

Tyre squirt is about the rotating boundary layer meeting the immovable object of the ground so rolling up. Then jetting around the tyre sidewall. So there's not a let you can do to influence the squirt vortex. But instead try to influence where it goes.

I'm not sure any "real" 2022 rear wings will have that profile.

Can we both agree that turbulence is good at mixing, just like its good at mixing an air and fuel mixture? Or the low pressure caused by the intake stroke?

If air is seeking equilibrium/stillness. It's faster to use turbulence to induce said equilibrium. Nature always seeks the path of least resistance.

You call the diffuser air energized/accelerated, I agree. The turbulent air from the tire is high pressure slow at the front, especially where the tire meets the road. Behind the tire it is the opposite.

That pressure differential is the squirt. If this flow fills the low pressure in the diffuser. The pressure rises, the accelerated low pressure air mixes with the slow turbulent air from the tire.

This raises the pressure at the diffuser, now the diffuser offers more pressure to be overcome by the air upstream. It is choked, in the relative sense that it cannot accelerate as much air.

If I stick a bunch of paper towels in my toilet, it is choked, in the sense that water cannot pass easily. Is there a more nuanced technical term, or elegant formula that can convey the way tire squirt chokes the diffuser?

Yes you absolutely can influence the tire squirt, with the tire itself no less.

[godlameroso]

Funny how this guy's CFD pretty much agrees with everything I've been saying. It's just more dumb luck.

[godlameroso]

RB15 on the left Mercedes on the right.

You can see Mercedes places more emphasis on the brake ducts, whereas RB15 tries to get really clean vortices from the diffuser and rear wing.

It's not entirely accurate but the gist of it is more or less there.

With the stream lines you can see why the serrated edges of the diffuser would come in handy.

As we can see, the diffuser central section has the highest velocity air, the strakes, create a laminar divergence, two counter rotating vortices form as the central section creates a low pressure opening for the air upstream to shoot right on by.

All the vortices at the rear of the car benefit each other. There's a few key details that are being left out, they cannot be computed easily.

[godlameroso]

As you can see, viscous forces play a bigger role the faster air moves, despite distance from the center of rotation. However at a critical distance the viscous forces play a lesser role, of course temperature affects this viscous force.

viewtopic.php?f=6&t=29819

Because the underside of the wing has high velocity air, the viscous forces force interaction with the end plate retraction; along with all the other vortices back there.

[Just_a_fan]

https://files.catbox.moe/zfwk1i.jpg

RB15 on the left Mercedes on the right.

You can see Mercedes places more emphasis on the brake ducts, whereas RB15 tries to get really clean vortices from the diffuser and rear wing.

It's not entirely accurate but the gist of it is more or less there.

With the stream lines you can see why the serrated edges of the diffuser would come in handy.

As we can see, the diffuser central section has the highest velocity air, the strakes, create a laminar divergence, two counter rotating vortices form as the central section creates a low pressure opening for the air upstream to shoot right on by.

All the vortices at the rear of the car benefit each other. There's a few key details that are being left out, they cannot be computed easily.

You did see the bit where he said he had an issue with the Red Bull mesh in the diffuser throat area, yes? Until he sorts that and reruns it, the comparison is suspect as are any conclusions drawn from it.

[godlameroso]

Even teams with multi million dollar super computers don't have perfect meshes. The teams trust their tools even when they have "correlation" issues. Which is really just a euphemism for lack of knowledge and or awareness.

[godlameroso]

Nevermind false analogy/conflation with crowdphobic anxiety 'pressure', do a fact check:

Do any F1 body aero-flows reach the transonic range, or show 'shock' or 'choke' phenomena?
Some aspects, such as vortices & buffet may correlate.

I would suspect that some airflows are close to the .7 mach number that creates these compressibility effects. However the pressure analogy is correct. Pressure is pressure, whether it's you pumping iron or air lifting a plane, or pipes bursting. Good video though.

[Just_a_fan]

I would suspect that some airflows are close to the .7 mach number that creates these compressibility effects. However the pressure analogy is correct. Pressure is pressure, whether it's you pumping iron or air lifting a plane, or pipes bursting. Good video though.

I'd be very surprised if compressibility is even close to being an issue in F1. The fastest speed an F1 car has done in a race is over 100km/h slower than the speeds where compressibility is even considered to be starting to be an issue.

If local airspeed started to get in to the compressibility speeds, we'd see shockwaves developing and things would go wrong pretty quickly. A shockwave under the car, for example, would choke the floor leading to rear instability and much crashing in to the scenery.

[Dipesh1995]

I would suspect that some airflows are close to the .7 mach number that creates these compressibility effects. However the pressure analogy is correct. Pressure is pressure, whether it's you pumping iron or air lifting a plane, or pipes bursting. Good video though.

I'd be very surprised if compressibility is even close to being an issue in F1. The fastest speed an F1 car has done in a race is over 100km/h slower than the speeds where compressibility is even considered to be starting to be an issue.

If local airspeed started to get in to the compressibility speeds, we'd see shockwaves developing and things would go wrong pretty quickly. A shockwave under the car, for example, would choke the floor leading to rear instability and much crashing in to the scenery.

A free paper for y'all.
https://www.researchgate.net/publicatio ... racing_car