Can a Wind Turbine Improve the Efficiency of a Moving Car?

[The_Thinker]

If supposing we were to add a wind turbine connected to a generator to a moving car, would we be able to get the air flowing around the car to turn the turbine and therefore gain some energy? If it is possible, is it economical? if it is, is it practical? would there be a loss? would there be any gain in overall efficiency??

A friend of mine wants to do this project for collage and wants to implement this idea... I just want to know if it is practical or not...

So... what do you guys think?

 

[MaWM]

That depends what you mean by "wind". It is certainly possible to attach a sail to a set of wheels and have the ambient wind blow you around. That would cetainly be efficient.

On the other hand, if you mean the wind generated by the car moving through the air, then the engine creates that motion by moving the car forward. By capturing that wind to extract energy, you are slowing the car down and making the engine work harder. Even using the energy you extract, you will use *more* gas than you do now. That is to say, the system is less efficient than existing cars.

 

[Averagesupernova]

Search the forum on this. There was a lengthly thread about it.

 

[russ_watters]

This is a type 1 perpetual motion machine - it won't work because it violates conservation of energy.

 

[DaveC426913]

If supposing we were to add a wind turbine connected to a generator to a moving car, would we be able to get the air flowing around the car to turn the turbine and therefore gain some energy? If it is possible, is it economical? if it is, is it practical? would there be a loss? would there be any gain in overall efficiency??

A friend of mine wants to do this project for collage and wants to implement this idea... I just want to know if it is practical or not...

So... what do you guys think?

The catch is that the wind, acting on the turbine blades, causes drag. The energy you gain from the wind turbine is lost by the increased drag.

But here's a thought to all you who think this is a no-win setup: Who said the addition of a wind turbine has to <I>increase</I> drag? A car already has lots of drag from its forward-facing surfaces. If you punched a hole in one of these surfaces and put a wind turbine in, the overall drag of the vehicle would <I>decrease</I>.

 

[ank_gl]

first u increase the weight, so you need more fuel.
second the turning of blades involves work, which you are to supply with your moving air, ie moving car. hmmm moving car gives energy to turbine and the turbine gives energy back to car! so cooooool!
not much cool;)), you can never get greater or rather equal amount of energy back, that you spend on the turbine

 

[FredGarvin]

But here's a thought to all you who think this is a no-win setup: Who said the addition of a wind turbine has to <I>increase</I> drag? A car already has lots of drag from its forward-facing surfaces. If you punched a hole in one of these surfaces and put a wind turbine in, the overall drag of the vehicle would <I>decrease</I>.

You're assuming that the turbine has no induced drag itself. Also you are assuming that there would be no pressure drag created. Simply because you reduce the frontal area of the vehicle by placing a hole in it does not mean you are going to decrease drag.

 

[dimensionless]

This could work if the wind is perpendicular to the motion of the car. It is probably not economical in most regions. There might be exceptions in regions where there is very high wind, although I would expect that it would make the car more difficult to control. It is probably more practical to attach a large sail to the car.

 

[DaveC426913]

You're assuming that the turbine has no induced drag itself. Also you are assuming that there would be no pressure drag created. Simply because you reduce the frontal area of the vehicle by placing a hole in it does not mean you are going to decrease drag.

I was suggesting that a hole in the front with a turbine behind it would not have any more drag than no hole.

But now I'm questioning even that.

Ignore the turbine turning and ignore air passing through - i.ew. as of the turbine seized. Now you've got the equivalent of a deep, blind pocket on your car. That would be more drag than if you had no pocket.

 

[Danger]

This is a type 1 perpetual motion machine - it won't work because it violates conservation of energy.

You're reading more into the question than was originally asked. The Thinker didn't ask if the car could be powered by such a device, only if work could be extracted from the windmill. The answer to that is 'yes'. For instance, it could be used to recharge a cell phone or something similar if a 12V outlet wasn't available. It certainly wouldn't be efficient, but it could work.

 

[ank_gl]

You're reading more into the question than was originally asked. The Thinker didn't ask if the car could be powered by such a device, only if work could be extracted from the windmill. The answer to that is 'yes'. For instance, it could be used to recharge a cell phone or something similar if a 12V outlet wasn't available. It certainly wouldn't be efficient, but it could work.

the problem is that the energy given to turbine would be greater than the output of turbine. so where is the advantage? you won't carry a turbine to recharge your phones, would u??

 

[russ_watters]

You're reading more into the question than was originally asked. The Thinker didn't ask if the car could be powered by such a device, only if work could be extracted from the windmill. The answer to that is 'yes'. For instance, it could be used to recharge a cell phone or something similar if a 12V outlet wasn't available. It certainly wouldn't be efficient, but it could work.

The math for a turbine producing half the engine's ouput would look like this:

Car engine output: 10kW
Turbine energy production: 5kW

System thermodynamic efficiency (if all pieces were 100% efficient):
(10+5)/10=150%

Still a type 1 pmm.

The key words in the opening post are "gain some energy". Obvously you don't gain anything by doing this and that is what the OP was hoping to do.

 

[Danger]

Car engine output: 10kW
Turbine energy production: 5kW

Who the hell are you talking to that requires 5kW for a cell phone? I think that you're taking this astronomy hobby a tad too far.

The key words in the opening post are "gain some energy". Obvously you don't gain anything by doing this and that is what the OP was hoping to do.

Okay, I interpreted that differently. Given your approach, you're absolutely right. I thought that he just wanted to know if anything could be done by the wind.

 

[caslav.ilic]

Just a side note: "put propeller in your own wind" trick is quite a normal feature in airplanes, called the ram air turbine. Of course it's a waste overall, but when other electric generators are shot out and the airplane is left with kinetic energy only, it'll do.

--
Chusslove Illich (Часлав Илић)

 

[russ_watters]

Yeah, if the choices are to have no control of the plane or sacrifice some glide ratio to power your controls and instruments, the choice is easy.

 

[brewnog]

Now charging your battery using a wind turbine while the car is stationary, that's certainly viable.

 

[ank_gl]

having a wind turbine for battery charging is certainly not viable

 

[The_Thinker]

yeah... that's what I felt too actually... it could be done.. but it would be less efficient, so its a non-gain project... thanks for the replies guys...

 

[brewnog]

having a wind turbine for battery charging is certainly not viable

Take a look at the units used on caravans, mobile homes, narrowboats and motor boats.

 

[kach22i]

Now charging your battery using a wind turbine while the car is stationary, that's certainly viable.

Along with solar film/paint we are getting somewhere with this idea.

 

[ank_gl]

Take a look at the units used on caravans, mobile homes, narrowboats and motor boats.

i don't know, maybe they use that trick. i had a very interesting discussion on this very topic, when i joined college. and what we came out was that, IT AINT EFFICIENT.
when you run a wind turbine mounted on a car, you are actually putting up some resistance, that means source has to supply more energy. true you are getting your battery recharged, but the energy input has also increased.
although this example involves very little energy, similar lines will be true for an appreciable amount of energy

 

[ank_gl]

of course, if the primary concern is electricity, they are viable

 

[russ_watters]

Wind turbines on mobile homes are not meant to be used while the home is moving. The engine, of course, has an alternator...

 

[ank_gl]

The engine, of course, has an alternator...

oh yes

 

[brewnog]

Wind turbines on mobile homes are not meant to be used while the home is moving. The engine, of course, has an alternator...

Which is exactly why I said "while the car is stationary" in my first comment.

 

[ank_gl]

whats the point of having a wind turbine on a stationary car??

 

[russ_watters]

To produce power from the wind while the engine isn't running. To run lights, recharge batteries, play the radio, run the a/c, etc.

 

[ank_gl]

duh.. i meant why would someone carry a wind turbine to run lights, recharge batteries, play the radio, getting a pair of battery seems more of a good choice.
carrying a wind turbine adds weight, its not a good idea.
ok picture this, one fine morning you leave home and take your WIND turbine;)) with you in your car assuming you ll be listening to a lot of MUZIK on your radio with $$wind energy$$(saving some bucks), and 50 miles away from your place, near a lake(oh! its beautiful), and you find out that there is no wind! what now? it is not even dependable.

if the question is for feasibility, sure it is feasible
but if it is about practical situation, it is rubbish

 

[DaveC426913]

ok picture this, one fine morning you leave home and take your WIND turbine;)) with you in your car assuming you ll be listening to a lot of MUZIK on your radio with $$wind energy$$(saving some bucks), and 50 miles away from your place, near a lake(oh! its beautiful), and you find out that there is no wind! what now?

Wait. Your wind turbine will become useful again in less time than your unintentionally-dead batteries will.

 

[ank_gl]

ok come straight to the point, what is the size of the proposed wind turbine??
if it is a 12V dc motor being used as a generator, it ll do.

 

[toddly]

wind turbine drag versus jet engine?

So why does the wind turbine create so much more drag than a jet engine? Or do they both create similar amounts of drag and the jet engine produces more power because the compressed air is ignited?

I do not purport to have any knowledge on the subject, just trying to learn.

 

[ank_gl]

hey, wind turbine and jet engines are two different things. in laymens term, while a jet engine produces thrust by a rotating propeller, a wind turbine rotates because of the flow of air

 

[russ_watters]

So why does the wind turbine create so much more drag than a jet engine? Or do they both create similar amounts of drag and the jet engine produces more power because the compressed air is ignited?

I do not purport to have any knowledge on the subject, just trying to learn.

In one case, the air is pushing the turbine, in the other, the propeller is pushing the air.

 

[MacG]

Just some input to this discussion

Hi There Fellow Nerds

I have some input to this discussion.

Consider the case of a horizontal axis wind turbine mounted on a car.
Look at the case where you want to go directly in the upwind direction.
A first shot at the mechanics here could be obtained by just looking at the effects of the wind turbine, that is neglect non-ideal stuff like car drag, rolling resistance and transmission losses. Apply simple 1D momentum theory for how the rotor behaves (The most simple rotor aerodynamic model. This assumes an ideal turbine: no viscous (fluid-friction) losses, no rotation of the flow in the wake of the turbine, etc etc)
The results from 1D momentum theory basically states, that the thrust force on the wind turbine is
T=0.5*rho*A*Vrel^2*CT where CT=4*a*(1-a)
(rho=density of fluid; A=Area of wind turbine; Vrel=relative free stream velocity of the fluid, as seen by the turbine; CT=Non-dimensional Thrust coefficient; a=axial induction coefficient, a nondimensional factor saying how much the axial flow velocity is reduced in the rotor plane relative to the far stream value)
Analogousy, the power output from the turbine is
P=0.5*rho*A*Vrel^3*CP where CP=4*a*(1-a)^2
(CP=Non-dimensional Power coefficient)

Under the above ideal assumptions the maximum velocity of such a vehicle is determined from the equilibrium of the forces at top speed (obs: no inertial at this maximum, top speed). Remember, that since power equals force times velocity, the propulsive force obtainable from the power production on the rotor (at the velocity V of the vehicle) is P=Fprop*V => Fprop=P/V
Noting that the relative velocity seen from the turbine is Vrel=Vwind+V, so the equation for determining the top speed reads
P/V=T
Putting in Vrel=Vwind+V into the equations for P and T, and feeding all into P/V=T and reducing, we end with this result (after some slight manipulation)
V/Vwind=(1-a)/a

This expression actually goes toward infinity for a tending to zero. This is clearly unphysical, and is due to the assumption of negigible car drag, and the other ideal asumptions. However, it is clearly shown that if we have a free stream velocity that is not zero, we can make a car move straight into the wind. And if we design the car good enough, we can even make it go faster than the free stream velocty. Agains the wind!
Neat, right.
If you do similar considerations, including car drag, transmission loss, and account for non-ideality of the rotor, you still actually end up with a wind car that could go faster than the free stream velocity in the upwind direction.
But I don't think such a car is built.
Yet.
Let's see how fast the cars at the Aeolus contes in Holland will go. Here's a link to the contest site:

www.windenergyevents.com

I hope this post was not too nerdy :)

-Mac G

 

[russ_watters]

You can, of course, make a car powered by a wind turbine go directly upwind. The final velocity would be at the point where your efficiency cancells out the relative wind.