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

[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.

 

[Dieseltwitch]

In fact in a movie, i think it was air force one or something... they show an apu( aux power unit) that pops out with a turbine on it, when the aircraft has a loss of power for some reason.

 

[russ_watters]

Yes, that was mentioned earlier in the thread. It works great, but it does add drag.

 

[Danger]

What you yourself mentioned, Russ, is worth repeating.
When it's an aeroplane large enough that cable-type manual backup isn't feasible, it's certainly a smart move to trade off glide distance for controllability. It would be useless to glide half-way around the planet if you're upside-down and ass-first when you get there. I'd rather sacrifice a few kilometres and land on the wheels.

 

[h2oski1326]

In fact in a movie, i think it was air force one or something... they show an apu( aux power unit) that pops out with a turbine on it, when the aircraft has a loss of power for some reason.

Its called a Ram Air Turbine (RAT), I used to work on them. As Danger eluded to its purpose it to allow control of the aircraft during an emergency glide.

 

[Sjonnie]

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.

Such a car has been build at the Delft University of Technology. It worked. One of the important aerodynamic aspects of using wind energy is the LIFT principle. When a horizontal axis windturbine has wing-shaped rotorblades it will be able to rotate faster than the windspeed. This means a higher efficiency than drag-based windturbines.

However even with drag-based windturbines such a vehicle can be build. The drag of the vehicle should be minimized as much as possible. EXAMPLE: http://www.zeiltheorie.nl/wagentje.html

 

[Mike Cookson]

You could get a propeller to generate electrical energy however you would have exert more effort to keep the car at the same speed as there is now more drag, so you would probably end up burning as much fuel in your engine as you would produce with the turbine.

 

[MacG]

Such a car has been build at the Delft University of Technology. It worked. One of the important aerodynamic aspects of using wind energy is the LIFT principle. When a horizontal axis windturbine has wing-shaped rotorblades it will be able to rotate faster than the windspeed. This means a higher efficiency than drag-based windturbines.

However even with drag-based windturbines such a vehicle can be build. The drag of the vehicle should be minimized as much as possible. EXAMPLE: http://www.zeiltheorie.nl/wagentje.html

Yes. The final results from the theory I stated in my first post only apply to (ideal) lift based wind turbines.
However, the equation for determining the top speed
P/V=T
is always valid when neglecting drag on the rest of the car, rolling resistance and mechanical loss in the teansmission.
Including these contributions the equilibrium equation for determination of the top speed would look like this:
EtaMech*P/V=T+Dcar+RollResist
EtaMech is due to mechanical loss in the transmissin, Dcar is the car drag (~Vrel^2) and RollResist is the rolling resistance of f the car.
The interesting thing here is that from this expression it can be seen that any wind energy converter can make a car go in the upwind direction (as long as the power production is above zero), since the left hand side term can be as big as we want it to if the (car) velocity is low enough.
So it will move upstream with any wind energy conversion system. The question is how fast. One important parameter in that is the relationship between P and T, and this is much better for lift based conversion systems than for drag based, as you mentioned.

The link you supplied was fun.
Do you have any links for the Delft University wind turbine car?

-Mac G

 

[WindGenerator]

I have an idea, put on a geek propellor hat with a turbine, then an inverter that charges your cell phone, ride your bike to generate wind.. Oh, I think dilbert has already invented that.

:)

 

[Roy Dale]

The air flowing around the car is not what is turning the turbine because there is no air flowing around the car unless the wind is blowing. Luckily aerodynamic force does not require air to actually flow around an object, it only requires a difference in velocity between the object and the sometimes still air (relative airflow). The relative airflow in this situation is caused by the linear motion of the object through the air as well as the motion of the object while in the air (rotation). This is important because to determine aerodynamic force you must first determine the direction of relative airflow that caused it.

Drag can spin any wind turbine but if this is a lift based horizontal axis wind turbine similar to a propeller, the same lift that causes it to spin can greatly (depending on its speed of spin) oppose its forward linear motion. The more the blades spin the more the relative airflow starts to change to a direction more opposite the direction of spin and subsequently the increasing lift starts to tilt more rearward opposit the direction of its linear motion.

Drag is not defined as the aerodynamic force that opposes forward motion. Oh wait a minute that’s the way it’s defined in aeronautic texts books, this may be the reason pilots do not know the difference between lift and drag.

 

[Jimboo101]

The air flowing around the car is not what is turning the turbine because there is no air flowing around the car unless the wind is blowing. Luckily aerodynamic force does not require air to actually flow around an object, it only requires a difference in velocity between the object and the sometimes still air (relative airflow). The relative airflow in this situation is caused by the linear motion of the object through the air as well as the motion of the object while in the air (rotation). This is important because to determine aerodynamic force you must first determine the direction of relative airflow that caused it.

Drag can spin any wind turbine but if this is a lift based horizontal axis wind turbine similar to a propeller, the same lift that causes it to spin can greatly (depending on its speed of spin) oppose its forward linear motion. The more the blades spin the more the relative airflow starts to change to a direction more opposite the direction of spin and subsequently the increasing lift starts to tilt more rearward opposit the direction of its linear motion.

Drag is not defined as the aerodynamic force that opposes forward motion. Oh wait a minute that’s the way it’s defined in aeronautic texts books, this may be the reason pilots do not know the difference between lift and drag.

I'm no rocket scientist, but what about a dual set of counter-rotating blades on the same axis? Wouldn't the effect of two sets of blades spinning in opposite directions be to cancel out the lift caused by one set of rotating blades?

 

[irian]

I thought is good idea, because that is make like aeroplan, make you car have big power, less to use petrol, if you use wind turbine, that is make your car moving slow, in front your car have big drag force. like aero have big lift force to help plane to move to up but for renew energy you can try that, i have one e-book about wind turbine handbook, if you want to know you can download that in scribd.com. maybe the book can help you analyze factor and fabrication wind turbine.that is not econoical because you must add new compenet to connection wind energy with your car. thanks,


irian
ym : iriansyahputra
blog : http://irianpoo.blogspot.com/"

 

[DaveC426913]

I thought is good idea, because that is make like aeroplan, make you car have big power, less to use petrol, if you use wind turbine, that is make your car moving slow, in front your car have big drag force. like aero have big lift force to help plane to move to up but for renew energy you can try that, i have one e-book about wind turbine handbook, if you want to know you can download that in scribd.com. maybe the book can help you analyze factor and fabrication wind turbine.that is not econoical because you must add new compenet to connection wind energy with your car. thanks,


irian
ym : iriansyahputra
blog : http://irianpoo.blogspot.com/"

It will not work no matter how you slice it. The turbine spins by the force of air flowing through it. The reactive force of the turbine pushes back on the air. This creates drag. your vehicle will need to work harder in proportion to how much extra drag is placed on it.

The only energy you will generate with the wind turbine is that which is generated by the engine working harder. What you've got there is a rather inefficient device that converts gasoline into electricity.

 

[lightyears]

I say not to punch a hole in the car. I ask what if you take the surface that is resisting on the car and you take that resistence away to replace it with a turbine? That causes the same amount of resistence that it had orignally

 

[OmCheeto]

It will not work no matter how you slice it. The turbine spins by the force of air flowing through it. The reactive force of the turbine pushes back on the air. This creates drag. your vehicle will need to work harder in proportion to how much extra drag is placed on it.

The only energy you will generate with the wind turbine is that which is generated by the engine working harder. What you've got there is a rather inefficient device that converts gasoline into electricity.

If you slice a pickup truck into the equation it might work.

I think a bank of small turbines, placed behind and below the rear window of a pickup truck would both generate power and reduce the aerodynamic drag of the vehicle.

Imagine the following vehicle, and rather than the shell, a set of small wind turbines laid out in the same basic shape.

Personally, this idea would not be economically feasible to either construct or install, as 90% of my commutes are at speeds of between zero and 35 mph. But someone who spent 90% of their time at freeway speeds in a pickup truck would notice an improvement.

But then again, the shell from the picture above would probably do the same thing, at 1/100th the cost.

 

[ank_gl]

I say not to punch a hole in the car. I ask what if you take the surface that is resisting on the car and you take that resistence away to replace it with a turbine? That causes the same amount of resistence that it had orignally

No, it doesn't happen like that

 

[sasi_skv]

i read in an article that, if we channel the wind to the generator, it will increase drag force to the car. so, the car's speed will decrease.
I also doing research about wind energy.
Are you doing this research?

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?

 

[DaveC426913]

If you slice a pickup truck into the equation it might work.

I think a bank of small turbines, placed behind and below the rear window of a pickup truck would both generate power and reduce the aerodynamic drag of the vehicle.

Still no.

In order for the turbines to generate power, they must produce drag.

 

[OmCheeto]

Still no.

In order for the turbines to generate power, they must produce drag.

True. But the design of trucks is so dreadfully bad in the first place, I can't imagine something streamlining the back end, not making the vehicle more efficient, even a bunch of mini-turbines.

But as I think I implied in my previous post, simply making the vehicle more aerodynamic is much more economical. And I should probably add now, that it is the only logical solution.

The article associated with the image of the truck I posted, stated that the gas mileage went from 25 to 32 mpg @ 70 mph, a 28% improvement. I agree with you that a slew of mini-me turbines, strategically placed, would probably not come close to generating such an improvement.

 

[russ_watters]

True. But the design of trucks is so dreadfully bad in the first place, I can't imagine something streamlining the back end, not making the vehicle more efficient, even a bunch of mini-turbines.

Adding wind turbines the the back end of a truck does not make it more streamlined, it makes it less streamlined (as was already said). Adding a turbine to anything makes it have more drag than it had before you added the turbine.

 

[dec2012omg]

I was thinking about this last night.
Surely a wind turbine on top of a car as it travels at speed would generate free energy.
Even if it only powers 20% of the car, this would be a great success for our planet.

I think it is definitely possible. One of us just needs to design it and show the formulas to prove it would be more fuel efficient. 'The energy is in the wind'

 

[Borg]

I think it is definitely possible. One of us just needs to design it and show the formulas to prove it would be more fuel efficient. 'The energy is in the wind'

The point is that the formulas have been determined a long time ago. They are basic and clear. You can't get something for nothing. If you get power from the wind, it ultimately came from the power that you put in via gasoline.

 

[xxChrisxx]

It would yield a net loss in energy.

Remember this golden rule:
When searching for efficiency, anything that affects the thing you want will yield a net loss.We are using an engine to push the car forward, the point is that using this motion to power a wind turbine will take speed fromthe motion, meaning the engine has to work harder to push the car forward.

engine > motion > wind turbine

As you can see adding a wind tubine to a car is basically just powered by the egine enyway.

However if you had a wind tubine that operated only when the engine was not causing motion (going down a large hill say) THEN you would get a gain.

TO get "free" energy (you don't get something for nothing), you need to get it from things that would otherside be thrown away.w Which is why adding a tubine to the exhaust would work.

 

[russ_watters]

I was thinking about this last night.
Surely a wind turbine on top of a car as it travels at speed would generate free energy.
Even if it only powers 20% of the car, this would be a great success for our planet.

I think it is definitely possible. One of us just needs to design it and show the formulas to prove it would be more fuel efficient. 'The energy is in the wind'

Welcome to PF. I'm not sure how to explain it any clearer than it already has. The wind moves a wind turbine by appying a force to it in the direction the wind is moving. In other words, for a wind turbine on top of the a car moving forward, the wind pushes it backwards -- slowing the car.

 

[pronjay]

OK so the turbine causes drag, but you have the momentum of the car so maybe you would get a slight overall net gain of energy i.e. enough to power a mobile phone...?

 

[pronjay]

Still no.

In order for the turbines to generate power, they must produce drag.

yeah but you have the momentum of th vehicle so doesn't this more than counteract the drag?