Air to Bodywork energy transfer?

[___]

Air is not a form of energy.

Adding a vortex to the air is not taking energy out of the air, it's taking energy out of the car, in the form of drag, and adding it to the air in the form of movement.

That's merely a question of your chosen inertial frame. Follow the car and the kinetic energy in the air is as clear as day. Vortices can contain concentrations of kinetic energy but much of that is "borrowed" from potential energy at their cores. Overall they're a loss of energy from the free stream, energy which is transmitted to the body which shed them unless the engine works equally hard pushing the car in the opposite (forwards) direction.

No, air doesn't give energy. We all might percept air as the flowing force over the car, but it's actually the car slicing through the air. In a wind tunnel you are in fact correct.

Look, if you want to be absolutist about it, you would be better off saying the car gives the air kinetic energy when it's travelling west and reduces its kinetic energy when it's travelling east, since the air actually has a velocity of about 108,000 kph in the direction of the earth's orbit around the sun, which at midday is east to west. Your choice of inertial frame fixed to the ground is a perfectly valid way to think about the problem, but from a physics point of view the fact that the air has no kinetic energy in that inertial frame is a reflection of the way you're looking at it, not an absolute property of the air.

From the perspective of a car driving round a track, the energetic properties of the air are identical to those seen from the perspective of a car installed in a wind tunnel. The energy in one system is no more nor less real than in the other, and since the way that energy is either conserved or dissipated is an extremely useful way to think about the forces on the car, I would implore you not to dismiss it out of hand.

[beelsebob]

Look, if you want to be absolutist about it, you would be better off saying the car gives the air kinetic energy when it's travelling west and reduces its kinetic energy when it's travelling east, since the air actually has a velocity of about 108,000 kph in the direction of the earth's orbit around the sun, which at midday is east to west.

No, the car puts energy into the air in both cases. The fact that the velocity in one direction in your reference frame drops is irrelevant. The energy still went into the air to accelerate it.

Your choice of inertial frame fixed to the ground is a perfectly valid way to think about the problem, but from a physics point of view the fact that the air has no kinetic energy in that inertial frame is a reflection of the way you're looking at it, not an absolute property of the air.

From the perspective of a car driving round a track, the energetic properties of the air are identical to those seen from the perspective of a car installed in a wind tunnel.

Indeed, and in both reference frames the effect is the same, the energy level in the air increases as it passes over the car, the energy level in the car decreases because of the air passing over it.

That is to say, the car is not taking energy out of the air.

[Owen.C93]

It wasn't a serious statement, just a way to look at things. The harder the car infront works the air the less that car behind has to work with in a correlated way.

If you're interested the quote actually came from Mike Elliot, head of Aero at Mercedes GP

[beelsebob]

It wasn't a serious statement, just a way to look at things. The harder the car infront works the air the less that car behind has to work with in a correlated way.

Indeed, the harder the car in front works the air, the more the air is flowing in unusual directions behind it, and the less the car behind's aerodynamics sees the flow it expects to see.

If you're interested the quote actually came from Mike Elliot, head of Aero at Mercedes GP

Right, this idea of "taking energy out of the air" gets bandied around a lot as a way of explaining what's going on to TV viewers. That doesn't mean it's actually true.

[___]

Indeed, and in both reference frames the effect is the same, the energy level in the air increases as it passes over the car, the energy level in the car decreases because of the air passing over it.

No it doesn't. Take the wind tunnel case if you find it simpler. The air quite simply does not have a higher average velocity after it interacts with the car.

[CBeck113]

Indeed, and in both reference frames the effect is the same, the energy level in the air increases as it passes over the car, the energy level in the car decreases because of the air passing over it.

No it doesn't. Take the wind tunnel case if you find it simpler. The air quite simply does not have a higher average velocity after it interacts with the car.

____, try looking at it from a single air molecule and a moving car. The velocity vector changes dramatically when the car drives past. For this case, let's say that this molecule passes between the nose and tire and is forced over the side pods. It will be forced in the direction of the car through the change (increase) in pressure caused by the car (solid object moving in a Newton fluid = no compression). The vector status of the molecule is [vx - , vy 0] (we'll leave off vz and pretend it doesn't move sideways). Next the molecule is close to the sidepods, and is forced upward. We have [vx - , vy +]. Now over the sidepods and down toward the diffusor [vx - , vy -], and this state basically remains until the molecule has passed the diffusor. At this point all chaos ensues due to turbulent air flow after the car has passed, and the vectors are in constant change (swirling, uncontrolled voritces). These are caused by the rapid change in pressure after the car has left, and its volume is being filled by the surrounding air.

So you are right that the average air velocity is dropping if anything, but the energy transfered from the car to the air is causing a velocity change, just locally. You forgot to look at the full system, since the air isn't "done" at the rear of the car, but goes into a turbulent state.

[___]

Indeed, and in both reference frames the effect is the same, the energy level in the air increases as it passes over the car, the energy level in the car decreases because of the air passing over it.

No it doesn't. Take the wind tunnel case if you find it simpler. The air quite simply does not have a higher average velocity after it interacts with the car.

____, try looking at it from a single air molecule and a moving car. The velocity vector changes dramatically when the car drives past. For this case, let's say that this molecule passes between the nose and tire and is forced over the side pods. It will be forced in the direction of the car through the change (increase) in pressure caused by the car (solid object moving in a Newton fluid = no compression). The vector status of the molecule is [vx - , vy 0] (we'll leave off vz and pretend it doesn't move sideways). Next the molecule is close to the sidepods, and is forced upward. We have [vx - , vy +]. Now over the sidepods and down toward the diffusor [vx - , vy -], and this state basically remains until the molecule has passed the diffusor. At this point all chaos ensues due to turbulent air flow after the car has passed, and the vectors are in constant change (swirling, uncontrolled voritces). These are caused by the rapid change in pressure after the car has left, and its volume is being filled by the surrounding air.

So you are right that the average air velocity is dropping if anything, but the energy transfered from the car to the air is causing a velocity change, just locally. You forgot to look at the full system, since the air isn't "done" at the rear of the car, but goes into a turbulent state.

In a car-fixed inertial frame the car doesn't have any energy to transfer to the air. You're right to think of the full system, not the local behaviour around different regions of the car. Think of that in terms of Newton's laws of motion. The air exerts a drag force on the car in the rearwards direction. The car therefore exerts an equal and opposite force on the air in the forwards direction (third law). That force produces a net acceleration in the same, forward, direction (second law). Exerted on air that has an initial velocity in the rearward direction, that forward acceleration is a deceleration in the direction of flow, and hence a loss of kinetic energy.

By the way, I appreciate this has long since departed from the subject of the RB10, but Owen.C93 made a perfectly valid point that was dismissed using faulty physics, and that needs to be corrected. It would seem sensible for a moderator to split the discussion. I know that the results of Galilean equivalence can seem to conflict with intuition but I promise you this is correct.

[turbof1]

Topic split off from red bull RB10. Please do continue the discussion here; it's interesting.

[___]

Thanks for preserving this turbof1. I shall just note that the split title raises some interesting questions...

In steady state conditions in a car-fixed inertial frame, the energy in the air is clearly not transferred to the bodywork, because the bodywork is in a steady state of zero kinetic energy. So where does it go? Clearly some of it is converted to heat through viscous damping. But you'll note that while in any inertial frame the air undergoes the same change in velocity and in the same direction, the air loses more energy in a car-fixed inertial frame than an earth-fixed inertial frame because the difference of squares of velocity is larger. But in both cases the heat added to the air is the same, so there must be at least one other flow of energy in the system which changes with the chosen inertial frame.

I think part of the answer may lie in the fact that in resisting the drag the car imparts a third-law acceleration to the earth in the rearwards direction. Defining a closed steady-state system with all energy accounted for is not simple. If anyone can think of a clearer way to look at it that would be interesting!

All the same, that doesn't prevent observing the forces, accelerations and changes in energy for part of the system, in any inertial frame...

[johnsonwax]

I think people are confusing work and energy.

When the car moves forward it does work on the air around it - it creates a high pressure area (the high pressure is potential energy stored up) in front of the car to push the air out of the way. And then after the car passes, additional work is done when the air returns to the low-pressure area behind the car (the potential energy is all expended). There's no net energy transfer, because the air afterward has no greater capacity to do work than it did before - the state of the air after the car passes is roughly identical (we're ignoring thermodynamic effects at this point) - temperature and pressure are the same. So, the car does work, energy is expended, but the air doesn't retain any of that energy.

The real transfer of energy is through thermodynamics. The engine is converting chemical potential energy (gasoline) into both mechanical work and heat. The mechanical work is transferred both to the road (resulting in more heat through friction, and some rotational work to the planet) and to the air. The heat from the engine, along with the heat from road friction, brakes, etc. all get transferred to the air, but the air quickly distributes that heat in a way that you don't notice. And that's the real energy transfer - we heat up the air. Most of the energy unlocked from the gasoline goes straight into the air in the form of heat.Some work goes to rotate the planet - but no energy because the races are a loop - so they're doing the same amount of work rotating the planet in one direction as they are rotating it in the other. The air heating up does have greater capacity to do work - manifested as wind (storms, tornadoes, hurricanes, etc).

Effectively, running a race with 100l of fuel and setting a drum with 100l of fuel on fire wind up being nearly identical in terms of energy transfer. It's just that the F1 car is doing a whole bunch of other kinds of work and energy conversion (about 40% goes through all of these other conversions, while about 60% is just heat straight out the exhaust as if you just set it on fire). Eventually it all winds up as heat going into the air.

[chuckdanny]

The state of affairs in physics is that what we, they call energy is a quantity that is eventually changing in nature but never change in total quantity. What is changing mostly is the quality of its nature whatever it is initially, potential energy (height above ground or deformation energy loaded in a spring, chemical potential in fuel etc...), heat, electrical energy etc... And this quality is resumed by another quantity that always increase for a closed system that is entropy. What it means is that while we can easily do works with stored potential energy, heat is a bad form of energy from which we can extract less work. It is related to order and disorder, in a combustion chamber the quick burn create a molecular liberation of kinetic energy. The mecanical system can extract part of this heat and kinetic explosion but lets very basically think of what happend, half of the molecule push the piston while the other half push the chamber which cannot move so half of the energy is already lost. Of course that's a big simplification but that's just to get the idea. This explosion is a very disordered process by itself but also because to favor a good combustion a swirling flow with turbulence is desirable.
So to get back to the process of downforce generation of a car going through the air what happend is that in a way, that's really a simplification i know, the air to generate downforce efficiently (with a good lift to drag ratio) is expected to flow in a pretty ordered state which is called laminar. But whatever the ratio the car has there will be turbulent air after the car has gone through it that is a change in the ordered state that the air was in.
But was it really ordered ? Is a gaz ordered ? In a way the large swirling eddies are much ordered, that's pretty hard to think but we could imagine some kind of mini drones that would benefit from those movement and charge an electrical battery. So there is temporarily at least an energy that is available to those drones that wasn't there before the F1 car smashed through it.
So in a way the question you ask is was this energy already present in the air and the car made a part of it available to do work and generate electrical potential energy or is it coming from the car ?
I think it all comes from the car, the movement through the air create pattern in the airflow around it that is order ! And from this order comes an available potential energy able to do work. This work is transfered through the tires wich are compressed like a spring and when they liberate this compression it generates tire forces.
The good ordering of the flow by the aerodynamic pieces enable a good transfer of energy through the tires.
And the fact that there is good quality energy available to my drones is the proof that something has been lost at least for the car.
To generate work a thermodynamic machine needs a hot source and a cold one that is an initial ordered state, a capacitor an ordered state in term of electrical charge, an aerodynamic machine a ordered state in term of pressure difference. What create this state is the car itself.
FOr the fuel as another exemple, it's cold and pretty ordered before ignition (complex molecular composition), after its very hot and the molecular byproduct are simpler.
The relation with information is to my understanding that the poorer state of energy that is heat is so because to extract 100% of work you should get a sensor, a device that knows the position of every molecules in a gaz for exemple and catch the kinetic energy as a molecular piston. But how do you know where is going every molecule and even if you could know, you would need energy to throw your catching molecular pistons.
As for the wind, its an ordered macro movement coming from the fact that earth atmosphere is also a thermodynamic machine and it is moving which creates coriolis forces that generates swirling movement.

But what i don't understand is that physicists speaks about the increase of entropy for the universe but it is cooling and more and more complex so maybe i understand absolutely nothing of this entropy concept...

[rjsa]

Don't get me wrong I am not trying to be a smarta.s.s.,
But as you know energy is never lost, so when the kinetic energy of a head-wind hits the front wing of the RB10,
where does it end up?

Increases the universe's entropy.
So yes, the energy is lost for pratical applications.

[TinoBoost]

What if I told you that downforce produces almost no work. Only in the energy stored in the suspension springs come from?

What if i told you that downforce mostly heats up the air? e.g. thermal energy? even without gravity the change in potential energy of the air is negligible. and the air disturbance quickly calms down.

This discussion is breaking most laws of physics.

The fact is all energy produced by an F1 ends up heating the track or the air.

There is no energy transfer between the air to the bodywork, unless the bodywork is spring loaded, and only at transient.

In either frame,car or ground, all energy is produced by the engine.

And energy does not care about a frame of reference, and is not absolute. A Change in energy is what matters.

So in steady state, at stable speed, neither the car nor the air is changing significant kinetic energy.
(Sure the air is a energy vector field, and there are a lot of changes locally and in small distance from the car, but in total racing does not produce wind)
Yet, there is downforce. Yet there is power produced by the engine. Well its all heat, our lovely form of energy.

[Lycoming]

What if I told you that downforce produces almost no work. Only in the energy stored in the suspension springs come from?

This is true if we assume everything else to be infinitely rigid, however, unless you show some numbers, I don't think you can say that the work done in spring compression is small.

There is no energy transfer between the air to the bodywork, unless the bodywork is spring loaded, and only at transient.

What about the drag force?

So in steady state, at stable speed, neither the car nor the air is changing significant kinetic energy.

So, at drag-limited top speed, the engine is not doing work on the car?

[beelsebob]

So in steady state, at stable speed, neither the car nor the air is changing significant kinetic energy.

So, at drag-limited top speed, the engine is not doing work on the car?

He said kinetic energy. Clearly chemical potential energy is being transformed into heat quite a lot.