General aero discussions

[AR3-GP]

Those limits are quite big, rolling rate limit of 1°/s is not as bad as the same yawing limit, but it's still probably 3-5 times slower than what happens to the real car. Front and rear ride height are same, 33mm/s is quite slow. I expect this is also 5-10 times slower than actual rates. The longer lasting period of time on track is the state itself, not the transition to that state.

If transition rates from state to state matched the order of magnitude of what happens on the track, I think WT models and moving mechanisms would have to be far sturdier to support much bigger dynamic loads. This would also mean much more powerful (thus bigger) servos that provide power to those mechanisms.

Replied to another thread, as this has nothing to do with RB20 itself

Interesting. It would probably be useful if the model motion systems were more powerful, and they were allowed to run them at higher transition velocities (with a suitably robust model). You might discover some transient flow instabilities that you were not aware of. Given that the real car is fitted with pressure sensors and push rod load cells, I wonder what would be visible in that data. Do those sensors have a fast enough response time to capture such effects?

[Vanja #66]

Interesting. It would probably be useful if the model motion systems were more powerful, and they were allowed to run them at higher transition velocities (with a suitably robust model). You might discover some transient flow instabilities that you were not aware of. Given that the real car is fitted with pressure sensors and push rod load cells, I wonder what would be visible in that data. Do those sensors have a fast enough response time to capture such effects?

Sensors are not an issue, you can set sampling rate far above 0.001s, ie 1000Hz, but you don't really need this even if you want to capture transient effects.

Like I said, transition from state to state takes a lot less time than actually spending time in any said state on track. On top of that - if you have a separation that causes a significant drop in load at a static state, it won't matter when it happens. If you don't have any separation in static state in WT, it's very unlikely that you had it during transition. Once separated, the flow needs a lot of encouragment to reattach, like introducing some suction on the wall (in our case, bodywork) and as we know - that's very illegal in F1

This is why bouncing was and is such a big issue, you can have a non-aero related disturbance cause a vertical movement of the car that leads to critical separation and this then kickstarts the porpoising phenomena. The core of this issue is hysteresis between aero and suspension reaction, but also the fact that detached flow won't reattach at exactly the same geometric conditions of initial detachment - you have to get geometry well inside the "safe" zone for that.

Fluids, like everything else, follow the path of least resistance. If it takes more energy to detach, they stay attached. When you included the losses, the energy requirement of reattachment is higher than that of initial detachment (simplified explanation to the best of my own understanding)

[majki2111]

I have a question. In 37:30 minute mark he starts talking about something about wheel rim and heat transfer. Is he talking about heat transfer trough gasses and heat flux. Flux is greater the more convective transfer is more pronounced. The greater Reynolds number is, the less resistance there is to transfer the heat. That is some standard stuff in chemical engineering courses. For me it was 2nd year.

Am I missing something? It cant be that those guys would be scratching their heads over 2nd year of chemical engineering fundamentals, right????

[Zynerji]

General aero q that I'm sure has been brought up before.

A friend asked me if they use hydrophobic/oleophobic coatings to reduce surface drag on the cars. He said they use a type of ceracoating(sp?) at his employer to make cruise missiles for this reason, but I was unsure about F1...

Any insight here?

[G-raph]

I have a question. In 37:30 minute mark he starts talking about something about wheel rim and heat transfer. Is he talking about heat transfer trough gasses and heat flux. Flux is greater the more convective transfer is more pronounced. The greater Reynolds number is, the less resistance there is to transfer the heat. That is some standard stuff in chemical engineering courses. For me it was 2nd year.

Am I missing something? It cant be that those guys would be scratching their heads over 2nd year of chemical engineering fundamentals, right????

He is talking about using "rim heating" to heat the tyre.

Rim heating is easy, you just expose the wheel rim to the hot brake disc, and radiation and convection (which will increase with Reynolds number (= car speed) as you say) will transfer the heat from the brake disc to the rim. That's your 2nd year standard stuff.

What he is talking about is the ability for the heated rim to transfer its energy to the rubber tyre.

Standard simulation tools, and their associated physics, will indicate that it will take around 1h for the tyre to recieve the energy from the rim. So F1 engineers dismissed the idea of using rim heating to control tyre temperature.

But that's because these simulations assume a steady state, where the car is travelling at constant speed (like in a wind tunnel or CFD). In that case, the rim, the air inside the tyre, and the tyre rubber will all rotate at the same speed. Therefore there will be no conductive heat transfer as there is no velocity difference between the air and the rim surface. The rim is not hot enough for radiation to be a significant heat flux, and conduction trhough the air will also be very small (due to air properties). And so it will take a long time for the heat to transfer from the rim to the air, and then from the air to the tyre. That can be verified in real life with a similar dyno test.

Neway says that it is only when you take the transient effect into account that you can understand how the system works on the racetrack, and therefore you need to ignore the physics behind the simulation tools.

An F1 car is constantly accelerating or decelerating, and the air inside the tyre will have its own inertia. Which means it will most of the time be rotating at a different speed to the rim and the tyre. Thus generating a convective heat transfer between the rim and the air, and then the air and the tyre. This means the tyre temperature will increase much more quickly than in the steady state condition described above.

It sounds obvious in hindsight, but as engineers it is difficult to question the science behind the simulation tools you use every day. That's Newey's point in this particular case.

[G-raph]

General aero q that I'm sure has been brought up before.

A friend asked me if they use hydrophobic/oleophobic coatings to reduce surface drag on the cars. He said they use a type of ceracoating(sp?) at his employer to make cruise missiles for this reason, but I was unsure about F1...

Any insight here?

Short answer : no.

Friction drag is very small on an F1 car compared to its pressure drag. Also, the flow turns turbulent pretty quickly so those coatings would only slightly delay the laminar to turbulent transition, and make almost no difference to the friction drag value.

All this would do is add some weight, which F1 engineers hate. They prefer to expose rough carbon fibre panels rather than paint it, so imagine with another layer of fancy coating on top of it.

Having said that, I know of some instances of hydrophobic coating being used on front and (mainly) rear wings in the wet, to avoid water droplet sticking to the wing's surface and effectively changing its shape, which could trigger a stall. But that has nothing to do with reducing drag.

Hope this helps.

[Tommy Cookers]

... An F1 car is constantly accelerating or decelerating, and the air inside the tyre will have its own inertia. Which means it will most of the time be rotating at a different speed to the rim and the tyre....

won't it also be rotating at a different speed because ? .....
tyre constriction (the flat bit always at the bottom) contributes displacement of the air amounting to under-rotation

[Zynerji]

General aero q that I'm sure has been brought up before.

A friend asked me if they use hydrophobic/oleophobic coatings to reduce surface drag on the cars. He said they use a type of ceracoating(sp?) at his employer to make cruise missiles for this reason, but I was unsure about F1...

Any insight here?

Short answer : no.

Friction drag is very small on an F1 car compared to its pressure drag. Also, the flow turns turbulent pretty quickly so those coatings would only slightly delay the laminar to turbulent transition, and make almost no difference to the friction drag value.

All this would do is add some weight, which F1 engineers hate. They prefer to expose rough carbon fibre panels rather than paint it, so imagine with another layer of fancy coating on top of it.

Having said that, I know of some instances of hydrophobic coating being used on front and (mainly) rear wings in the wet, to avoid water droplet sticking to the wing's surface and effectively changing its shape, which could trigger a stall. But that has nothing to do with reducing drag.

Hope this helps.

Thanks! I definitely appreciate the response!

[majki2111]

He is talking about using "rim heating" to heat the tyre.

Rim heating is easy, you just expose the wheel rim to the hot brake disc, and radiation and convection (which will increase with Reynolds number (= car speed) as you say) will transfer the heat from the brake disc to the rim. That's your 2nd year standard stuff.

What he is talking about is the ability for the heated rim to transfer its energy to the rubber tyre.

Standard simulation tools, and their associated physics, will indicate that it will take around 1h for the tyre to recieve the energy from the rim. So F1 engineers dismissed the idea of using rim heating to control tyre temperature.

But that's because these simulations assume a steady state, where the car is travelling at constant speed (like in a wind tunnel or CFD). In that case, the rim, the air inside the tyre, and the tyre rubber will all rotate at the same speed. Therefore there will be no conductive heat transfer as there is no velocity difference between the air and the rim surface. The rim is not hot enough for radiation to be a significant heat flux, and conduction trhough the air will also be very small (due to air properties). And so it will take a long time for the heat to transfer from the rim to the air, and then from the air to the tyre. That can be verified in real life with a similar dyno test.

Neway says that it is only when you take the transient effect into account that you can understand how the system works on the racetrack, and therefore you need to ignore the physics behind the simulation tools.

An F1 car is constantly accelerating or decelerating, and the air inside the tyre will have its own inertia. Which means it will most of the time be rotating at a different speed to the rim and the tyre. Thus generating a convective heat transfer between the rim and the air, and then the air and the tyre. This means the tyre temperature will increase much more quickly than in the steady state condition described above.

It sounds obvious in hindsight, but as engineers it is difficult to question the science behind the simulation tools you use every day. That's Newey's point in this particular case.

Yes, yes, yes. I understood what he is saying about air in the tyre and inertia. Those concepts are easily understandable with masters degree in chemical/material engineering. To bad market here in Zagreb, Croatia doesn't offer such a job.

Ia was just looking into how much stuff I understand with a degree I have.

[G-raph]

... An F1 car is constantly accelerating or decelerating, and the air inside the tyre will have its own inertia. Which means it will most of the time be rotating at a different speed to the rim and the tyre....

won't it also be rotating at a different speed because ? .....
tyre constriction (the flat bit always at the bottom) contributes displacement of the air amounting to under-rotation

No.

Although you are right that the tyre velocity is slower near the ground than at the top (because of the deformation), it makes no difference to the heat convection problem. Each point of the tyre, the air inside the tyre, and the rim rotate at a speed which only depends on their local distance to the axis of rotation (considering a steady state, as discussed before). So even if the tyre velocity is not usniform, there is no local difference of velocity between the air inside the tyre and the rim.

Yes, yes, yes. I understood what he is saying about air in the tyre and inertia. Those concepts are easily understandable with masters degree in chemical/material engineering. To bad market here in Zagreb, Croatia doesn't offer such a job.

Ia was just looking into how much stuff I understand with a degree I have.

Sorry I misunderstood your post, my bad. I thought you asked a question.