Harnessing Wind Energy From a Car for Fuel Efficiency

[ArielRodriguez]

First of all, I have read some of the previous posts that related to this topic, but they are closed.

I am not looking to solve the world's energy crisis, but I was wondering if there was a way to harness some of the energy given off as friction from the drag of a car. I was looking at some of the embellishments on my excursion (clearly not made to be aerodynamic), and I found that there were several different grooves that could easily be made into something like a wind tunnel. So, my question is whether it would increase the drag to cut the ends open and install a small turbine, more so than it could create.
Please keep in mind that fact that there is already a preexisting body where it would be, so to simply say "it's impossible due to conservation of energy" is not helpful nor necessarily true.
EDIT: I may not have been clear enough as to what I was trying to ask. I would use the turbine as a generator for energy, to be used in the engine in some form or another. Specifically, I was looking at adding a unit that created Hydrogen from water, to enhance the gas and make the car more fuel efficient. But, being that cars are dreadfully inefficient, would it even be worth it in the end? That is, in the sense of energy, not dollars.

 

[A.T.]

I am not looking to solve the world's energy crisis, but I was wondering if there was a way to harness some of the energy given off as friction from the drag of a car.

If there is no true wind (relative to the ground), I don't think this makes sense for cars.

But airplanes, have to create lift, which induces vortices. And this specific loss form can be harvested with wind tip turbines (slide 21):
http://www.dept.aoe.vt.edu/~mason/Mason_f/WingtipDevicesS04.pdf
But it is probably simpler to use winglets and other shapes that reduce the vortices in the first place.

Another way for planes to recover energy lost to drag are boundary-layer ingestion engines. The body accelerates the air, and the engines recover some of that kinetic energy by working more efficiently, than in the freestream.
http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_09_30_2013_p40-619758.xml

As for ground vehicles, they can use the true wind relative to the ground to propel themselves. To go directly upwind, they need a turbine:

https://www.youtube.com/watch?v=F7PNSyAfCjk

 

[OmCheeto]

... would it even be worth it in the end?...

No. See Betz'[/PLAIN] Law.

Or list why you don't believe the conclusions from the other "Wind Turbine on a Car" threads:

Would a wind turbine on a moving car generate energy efficiently? (Wow. Just wow.)

add a wind turbine to a car?

Perhaps if we build a large, wooden Badger...

:thumbs:

ps. Welcome to Physics Forums!

 

[ArielRodriguez]

Fair enough. I hadn't seen that particular post, which would have saved me quite a bit of time...

 

[OmCheeto]

Fair enough. I hadn't seen that particular post, which would have saved me quite a bit of time...

I'm not trying to discourage you. Your question, and subsequent edit, show that you are not a dullard. Somewhere in this forum, someone posted something almost identical to what you did. I responded with something to the effect; "Idea stolen. Thank you."

I will have to find that person one day, and give him/her their $20,000,000 reward.


--------------------------------
Daddy Ombucks... Ha!
Ok to delete, infract, and ban.

 

[Baluncore]

Any turbine added to a car would increase drag and so fuel consumption more than it could possibly generate.

It is often possible to get a 20% improvement in fuel economy from a vehicle by the addition of airflow controlling profiles. You can also get a 20% advantage by driving 10% slower on the highway. Reducing the weight of the vehicle is also beneficial, especially in hill country or stop/start conditions in a city. These methods are way ahead of any co-generation available, which would actually cost you more fuel.

Some methods of reducing vehicle drag are; boattail plates or base flaps that reduce drag at the tail by confining the eddy flow behind the vehicle so as to not increase it's aerodynamic profile. Using skirts along the sides of the vehicle can have quite a significant benefit in cross winds.

Finding ways of increasing vehicle economy while remaining within the regulations and not obstructing other road users is a much better investment than researching co-generation.

 

[Malverin]

Drag and Power

Power of a wind turbine depends on it's Power coefficient Cp

and drag deppends on drag coefficient Cd

For lift type turbines, Cp is much greater than Cd

So it can produce more power, than the power you need to overcome the drag, it just can not extract all the wind power.

http://en.wikipedia.org/wiki/Wind_turbine_aerodynamics

http://cdn.intechopen.com/pdfs/16241/InTech-Aerodynamics_of_wind_turbines.pdf

 

[A.T.]

So it can produce more power, than the power you need to overcome the drag, it just can not extract all the wind power.

Only if you have true wind.

 

[Malverin]

Faster than wind

Sail boats can go upwind faster than the wind. It is well known fact

http://upload.wikimedia.org/wikipedia/en/thumb/0/0e/True_Wind_vs_Apparent_Wind.png/550px-True_Wind_vs_Apparent_Wind.png

It can be seen that a boat that can sail closer than 20 degrees to the apparent wind can make good upwind faster than the real wind.

http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind

 

[OmCheeto]

Any turbine added to a car would increase drag and so fuel consumption more than it could possibly generate.

It is often possible to get a 20% improvement in fuel economy from a vehicle by the addition of airflow controlling profiles. You can also get a 20% advantage by driving 10% slower on the highway. Reducing the weight of the vehicle is also beneficial, especially in hill country or stop/start conditions in a city. These methods are way ahead of any co-generation available, which would actually cost you more fuel.

Some methods of reducing vehicle drag are; boattail plates or base flaps that reduce drag at the tail by confining the eddy flow behind the vehicle so as to not increase it's aerodynamic profile. Using skirts along the sides of the vehicle can have quite a significant benefit in cross winds.

Finding ways of increasing vehicle economy while remaining within the regulations and not obstructing other road users is a much better investment than researching co-generation.

Did you ever see my post regarding my research of the NASA test vehicle studying this? It seems to confirm your statements. It was another variation of a "Wind Turbine on a Car" thread.

My favorite post from that thread was by Berkeman.

11 year olds have an excuse to be crackpots. All others are doomed to be italicized...

 

[Baluncore]

Yes I did. I am aware, but the OP asked a different question.

, but I was wondering if there was a way to harness some of the energy given off as friction from the drag of a car. I was looking at some of the embellishments on my excursion (clearly not made to be aerodynamic), and I found that there were several different grooves that could easily be made into something like a wind tunnel. So, my question is whether it would increase the drag to cut the ends open and install a small turbine, more so than it could create.

The subject of this thread appears to have now morphed from miniature surface turbines on/in the surfaces of the vehicle to major vehicle extensions in the form of wind powered vehicles.

 

[willem2]

No. See Betz'[/PLAIN] Law.

I don't think Betz' law is valid here. The reason that you can't get all the power of the incoming wind, with a stationary windmill, is because the windspeed behind the mill can't go to 0, because the air couldn't get away.

With a car windmill however, It doesn't matter that you can't slow down the wind to 0 (in the car frame), because the force on the car will be less if the wind isn't completely slowed down.

 

[rcgldr]

Assuming a zero wind (relative to the pavement) condition, then the power consumed by the turbine equals the net drag of the turbine times the speed of the car (ground speed and wind speed are the same). With any normal power conversion device, the power output is less than the power consumed (input), so the turbine on a car ends up being a net loss.

Regarding the other posts about wind powered vehicles, these require a non-zero wind speed relative the ground in order to function. I assume this was not the intent of the orginal post.

 

[berkeman]

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