AeroDynamic Drag, why fight it? Use it

[Evbwcaer]

If you put turbines anywhere the drag will definitely increase as a result, and the amount of energy generated will certainly be much lower than what's lost due to the increase in drag, since no system (and certainly not a mini wind turbine) has 100% efficiency.

I don't want to be belittling but please think of what you're proposing... Free energy anyone?

I don't see this as a "free energy" scheme or anything like a perpetual motion machine. In the case of a car moving through the air, you have conceded losses to wind resistance. Think about that, you have energy that you are going to lose to drag and you know it. The goal of the wind turbine is not to create energy, it is to lose less energy, huge difference and the reason why something like this is not against the laws of physics.

It does no matter that a wind turbine is not 100% efficient either, because you are working to reduce the loss of energy, not make energy.

Imagine the Jeep people are talking about, presumably has electric fans for the radiator. If those were acting as turbines during highway cruising, the drag would not increase and they would make energy...albeit not very much. The reason it is not free energy is because it is a trick to allow the jeep to waste less energy pushing air, and that is all.

 

[Johan]

I don't see this as a "free energy" scheme or anything like a perpetual motion machine. In the case of a car moving through the air, you have conceded losses to wind resistance. Think about that, you have energy that you are going to lose to drag and you know it. The goal of the wind turbine is not to create energy, it is to lose less energy, huge difference and the reason why something like this is not against the laws of physics.

It does no matter that a wind turbine is not 100% efficient either, because you are working to reduce the loss of energy, not make energy.

Imagine the Jeep people are talking about, presumably has electric fans for the radiator. If those were acting as turbines during highway cruising, the drag would not increase and they would make energy...albeit not very much. The reason it is not free energy is because it is a trick to allow the jeep to waste less energy pushing air, and that is all.

Sorry. This is wrong. The turbine does not turn freely! If it is to generate power there will obviously be resistance as the blades spin. This creates added drag. There is no such thing as generating energy, only converting it from one form to another.

 

[green1]

I don't see this as a "free energy" scheme or anything like a perpetual motion machine. In the case of a car moving through the air, you have conceded losses to wind resistance. Think about that, you have energy that you are going to lose to drag and you know it. The goal of the wind turbine is not to create energy, it is to lose less energy, huge difference and the reason why something like this is not against the laws of physics.

It does no matter that a wind turbine is not 100% efficient either, because you are working to reduce the loss of energy, not make energy.

Imagine the Jeep people are talking about, presumably has electric fans for the radiator. If those were acting as turbines during highway cruising, the drag would not increase and they would make energy...albeit not very much. The reason it is not free energy is because it is a trick to allow the jeep to waste less energy pushing air, and that is all.

Wrong.
if you have a place that air can flow that you can place a turbine, it is more efficient to leave that place empty so the air can flow freely through than it is to impede it with a turbine.

 

[Evbwcaer]

Sorry, but you are not asking the right question. I am not saying I am matter of fact correct, but I know you are not asking the right question, Johan.

Yes, if the blades generates power there will be resistance. However, if you have already conceded that resistance and it is pure waste, you know you are going to have it and there is no way around it, then salvaging some energy, and therefore using less but generating none in net, is probably possible.


You know how they cut circular holes in large banners to let the wind flow through more easily? Now imagine the banner is rigid and slightly dished so the air is funneled toward the holes, and holes have small turbines in them. Compare that scenario to the same rigid and dished banner, but this time with no holes and no turbines. The one with the turbines will be more aerodynamic AND that will be further offset by the power the turbines "make." Now, make this same shape the front of a car. Yes, a banner with holes only and no turbines would be the best.

Totally impractical and limited example, but it demonstrates a concept, that the banner with turbines is more aero than the one without and it "makes" energy.

Discuss

 

[green1]

You know how they cut circular holes in large banners to let the wind flow through more easily? Now imagine the banner is rigid and slightly dished so the air is funneled toward the holes, and holes have small turbines in them. Compare that scenario to the same rigid and dished banner, but this time with no holes and no turbines. The one with the turbines will be more aerodynamic AND that will be further offset by the power the turbines "make." Now, make this same shape the front of a car. Yes, a banner with holes only and no turbines would be the best.

You said it all in the bolded part. Nothing is gained by the turbines, their only possible purpose is to make the whole thing less efficient.
You start have a big solid wall, in which case the only way to add turbines is to cut holes in it, so you cut the holes, this makes you more efficient, then you spend a whole lot of money to add turbines, which REDUCES the efficiency that you just added.

What possible reason would you do that? (other than not understanding physics?)

 

[Evbwcaer]

Ok Green1, you said:

"Wrong.
if you have a place that air can flow that you can place a turbine, it is more efficient to leave that place empty so the air can flow freely through than it is to impede it with a turbine."

Please address the example of the radiator fans on the Wrangler. This is not a place that air can flow essentially or it could flow though fans only to be eventually stopped by the firewall or engine block. So you say I am wrong, but the case you make does not apply really.


Then you said:

"Nothing is gained by the turbines, their only possible purpose is to make the whole thing less efficient."

It makes the whole thing less efficient than a solid wall, but less efficient than the open holes. The real point though is that the example with the turbines is more aero than the example without, and the turbines produce some energy.

"What possible reason would you do that?"

In an automotive application, one would be to capture energy going down hill, for brake force, to generate energy when parked, as a way to convert liquid fuel to electrical energy or to capture some of the wasted energy.

I am not here to come up with the applications, I am here to have a discussion about if a wind turbine could make a vehicle less inefficient specifically.

 

[Johan]

Look, the only thing you can do in an automotive scenario is look at where you have energy lost to unnecessary conversation of kinetic energy to heat. In a car that will be breaking, which is why regenerative braking makes sense (in an EV or hybrid). Nothing else makes sense. Trust me, forget the wind turbines on the car, it's 100% impossible due to basic thermodynamics to gain anything from it. Take the banner thought example and apply to a car: yes, by all means make the car more aerodynamic if you can, to use less energy driving, but this has nothing to do with adding turbines (which, everything else equal, will always make total efficiency worse).

 

[green1]

Ok, first of all, PLEASE learn to use the quote tool... this is quite cumbersome to read.

Please address the example of the radiator fans on the Wrangler. This is not a place that air can flow essentially or it could flow though fans only to be eventually stopped by the firewall or engine block. So you say I am wrong, but the case you make does not apply really.

If the air can't flow, then the turbines wouldn't spin, so nothing would be gained. if the air can flow, then NOT having the turbines would be more efficient. Radiator fans move air, the compartment isn't sealed, the air moves out under the vehicle generally. (though horribly inefficiently)

It makes the whole thing less efficient than a solid wall, but less efficient than the open holes. The real point though is that the example with the turbines is more aero than the example without, and the turbines produce some energy.

No, having the turbines is ALWAYS less aero than without. And any energy created by the turbines is ALWAYS less than the amount of energy wasted to do so.

In an automotive application, one would be to capture energy going down hill, for brake force, to generate energy when parked, as a way to convert liquid fuel to electrical energy or to capture some of the wasted energy.
I am not here to come up with the applications, I am here to have a discussion about if a wind turbine could make a vehicle less inefficient specifically.

If you only ever drive down hill, sure, but realize you'll lose more energy going up the hill than you'll gain going back down.
If you want to brake, use the brakes, not a turbine that will be there even when you're trying to accelerate
When parked, this is the only possible place you might gain some, but if you want to overcome the weight penalty of lugging it around, you better be sure you park in a pretty windy spot, and then you have to set-up and tear-down the turbine each time. If you leave it fixed to the car even while driving, you're pretty much guaranteed to use more energy while driving than you gain while parked.
I'm not even sure what you mean by converting liquid fuel to electrical energy, we have things called engines that do that.

As for capturing wasted energy, the whole point is that this won't do that, it only wastes, it doesn't recover.

 

[Evbwcaer]

What you are not addressing though is if the shape of the vehicle requires a profile where the wind turbine would not decrease the aero profile of the vehicle.

I am not saying this is really practical, makes $$$ sense, etc. I am saying it is possible that it could work in concept.

Final example.

A hybrid snowplow, driving down the highway, not pushing snow, 65 mph. Very inefficient aerodynamically. Now, put a horizontal axis wind turbine in front of the plow, the radius of the turbine matches that of the plow exactly. The plow is there, you are not taking it off. The energy from the turbine is going electric drive motor. And I think, any electric drive going on is about 4 times more efficient than the liquid fuel drive it is supplementing.

We started off this discussion saying that the laws of physics prevented this concept end of story. Now, it seems, we are having a debate about practicality, implementation, etc. I agree, its probably a dumb idea, but who knows where technology, materials, etc. will go?

 

[Johan]

What you are not addressing though is if the shape of the vehicle requires a profile where the wind turbine would not decrease the aero profile of the vehicle.

I am not saying this is really practical, makes $$$ sense, etc. I am saying it is possible that it could work in concept.

Final example.

A hybrid snowplow, driving down the highway, not pushing snow, 65 mph. Very inefficient aerodynamically. Now, put a horizontal axis wind turbine in front of the plow, the radius of the turbine matches that of the plow exactly. The plow is there, you are not taking it off. The energy from the turbine is going electric drive motor. And I think, any electric drive going on is about 4 times more efficient than the liquid fuel drive it is supplementing.

We started off this discussion saying that the laws of physics prevented this concept end of story. Now, it seems, we are having a debate about practicality, implementation, etc. I agree, its probably a dumb idea, but who knows where technology, materials, etc. will go?

The wind turbines will always decrease the aerodynamic profile of the vehicle.

If you disagree with this I'm going to have to say this: I don't have the intellect to engage a person of your intellect in further discussion.

 

[green1]

What you are not addressing though is if the shape of the vehicle requires a profile where the wind turbine would not decrease the aero profile of the vehicle.

I am not saying this is really practical, makes $$$ sense, etc. I am saying it is possible that it could work in concept.

Final example.

A hybrid snowplow, driving down the highway, not pushing snow, 65 mph. Very inefficient aerodynamically. Now, put a horizontal axis wind turbine in front of the plow, the radius of the turbine matches that of the plow exactly. The plow is there, you are not taking it off. The energy from the turbine is going electric drive motor. And I think, any electric drive going on is about 4 times more efficient than the liquid fuel drive it is supplementing.

Nope, wrong again, if the turbine can turn, then it's interfering with air that is moving, that means you are increasing drag. Doesn't matter how inefficient your design is otherwise, this only makes it worse.

If you put up a big wall with a turbine in front of it, if the turbine touches the wall, no air will flow, so the turbine won't spin. No gain, small loss due to weight.
If you put up a big wall with a turbine in front of it, if the turbine is a ways in front of the wall, air will flow through the turbine, and around the wall, the turbine spins, but it is doing so by interfering with air that otherwise would have gone around the wall, so this is actually worse than the first scenario because now you have loss from the weight of the turbine, and more loss from the added interference with the airflow. meanwhile the turbine, at it's best, could only hope to recover some of the energy from the airflow, not all of it, and none of the weight penalty.
If you cut a hole in the wall, you increase your efficiency, but if you put a turbine in to that hole then you decrease your efficiency again. Not to mention, in your scenario, the wall is important, so you can't cut holes in it.

We started off this discussion saying that the laws of physics prevented this concept end of story. Now, it seems, we are having a debate about practicality, implementation, etc. I agree, its probably a dumb idea, but who knows where technology, materials, etc. will go?

No, nothing has changed, the laws of physics STILL prevent this concept, end of story. Now, it seems, you still don't understand that.

 

[Johan]

Rhetorical question: if it was possible to make cars, airplanes, trucks (anything that moves through air) more fuel/energy efficient by adding turbines that "capture energy that would otherwise be wasted by drag" (without adding new drag) - how come cars, airplanes and trucks don't have loads and loads of turbines on them?

Is it likely that all the aerospace and automotive engineers who ever lived have overlooked this opportunity?

 

[McRat]

The only wind turbine on a vehicle I know of is the emergency backup APU on a jet airliner. It deploys from the fuselage, spreads it's blades, and generates electricity to operate the instruments in an emergency.

So the tech exists, but it's not used normally due to the high amount of drag they create.

 

[HankLloydRight]

Also in the " AeroDynamic Drag, why fight it? Use it" department, 20 years ago a friend of mine suggested that airlines put turbine like blades on the wheels of their landing gear to serve two purposes -- one of course is to create more drag upon landing to slow the plane, and second, spin up the wheels to landing speed, so they don't chirp as much when they hit the runway and burn off a bunch of rubber. I always thought that was a good use/need for additional drag so increase the life of plane tires.

Of course, they would need to be retracted during take-off.

 

[Saghost]

Also in the " AeroDynamic Drag, why fight it? Use it" department, 20 years ago a friend of mine suggested that airlines put turbine like blades on the wheels of their landing gear to serve two purposes -- one of course is to create more drag upon landing to slow the plane, and second, spin up the wheels to landing speed, so they don't chirp as much when they hit the runway and burn off a bunch of rubber. I always thought that was a good use/need for additional drag so increase the life of plane tires.

Of course, they would need to be retracted during take-off.

That's actually not a horrible idea. Right now airlines/aircraft companies are exploring hub motors in one or more wheel sets for taxiing - letting the airplane back itself out of a gate, and also letting them keep the turbines off for longer (only have to wind up the big engines in time to be warm at takeoff.)

With a heavily electrified aircraft design like the 787, this seems fairly practical. If they also use the wheel motors to spin the wheels up for landing, they get the benefits you're describing. If there's enough capacity in the aircraft's battery pack, they could potentially do regenerative braking on landing...
Walter

 

[HankLloydRight]

That's actually not a horrible idea. Right now airlines/aircraft companies are exploring hub motors in one or more wheel sets for taxiing - letting the airplane back itself out of a gate, and also letting them keep the turbines off for longer (only have to wind up the big engines in time to be warm at takeoff.)

Well, in warmer climates, I'd hope they'd keep one engine idling to support A/C on the plane. Having been stuck on a plane, on the tarmack without A/C, I wouldn't want to have that an everyday occurrence especially at busy airports like Newark or JFK where you can sit on the runway for 45-60 minutes.

I like the regen idea!

 

[Evbwcaer]

Alright guys, I am making points that are being danced around.

First off all, in the concept of using it to recover energy going down hill....you would not lose this going uphill if 1) a fairing went over the turbine, 2) you traveled much more slowly uphill than downhill, and that seems logical.

Second....the reason this does not exist in the real world, is because, as it stands, it is totally impractical, and probably always will be. The point is that it is not against the laws of physics and may have limited applications.

Third....having a turbine is not "ALWAYS" going to make something less efficient in the real world. The reason is that you would be incorporating the turbine into the overall design of the vehicle. Take the Wrangler example. Instead of the air coming through the grill smashing into the perfectly vertical, perfectly flat firewall, it instead goes into a smooth flowing trumpet/funnel like tube, which exits out the back of the vehicle. Now, put a turbine in it. Since everyone has so clearly mentioned that it is not 100% efficient, if would not prevent airflow as well as the firewall, and it would make some energy.

Finally, if you want to use brakes for braking....don't drive a Tesla.

Double finally, somebody tell me what law of physics says this does not work? Remember.. I am not making energy, I am using less, also remember, turbos (aka turbines) make diesels more efficient. That is correct, they take energy to operate, they are not 100% efficient, they have friction, they generate heat and noise and vibrations, and make the whole deal more efficient.

 

[Saghost]

Well, in warmer climates, I'd hope they'd keep one engine idling to support A/C on the plane. Having been stuck on a plane, on the tarmack without A/C, I wouldn't want to have that an everyday occurrence especially at busy airports like Newark or JFK where you can sit on the runway for 45-60 minutes.

I like the regen idea!

Electric A/C on the 787, using a dedicated motor driven compressor to generate the high pressure air for the cabin for both pressurization and cooling (Boeing says it weighs less, consumes less engine power, and delivers cleaner, higher pressure air than the traditional main engine compressor bleed approach while requiring less maintenance and being more reliable.)

The APU has a big electric generator attached and not much else, so I'd imagine in that environment they'd be running the APU instead of the main engines.

- - - Updated - - -

Double finally, somebody tell me what law of physics says this does not work? Remember.. I am not making energy, I am using less, also remember, turbos (aka turbines) make diesels more efficient. That is correct, they take energy to operate, they are not 100% efficient, they have friction, they generate heat and noise and vibrations, and make the whole deal more efficient.

That point that several folks have been trying to make is that any design you can make with a turbine will have less drag if kept the same except without the turbine. The energy to drive the turbine has to come from somewhere, and it comes from the energy that's moving the car.

While it is certainly true that you could use some sort of switchable turbine to recover energy when you're slowing the car, you're adding weight and cost and complexity (and drag the rest of the time) - and your turbines probably aren't as efficient as regenerative braking is at recovering the energy.

 

[wdolson]

What you are not addressing though is if the shape of the vehicle requires a profile where the wind turbine would not decrease the aero profile of the vehicle.

I am not saying this is really practical, makes $$$ sense, etc. I am saying it is possible that it could work in concept.

Final example.

A hybrid snowplow, driving down the highway, not pushing snow, 65 mph. Very inefficient aerodynamically. Now, put a horizontal axis wind turbine in front of the plow, the radius of the turbine matches that of the plow exactly. The plow is there, you are not taking it off. The energy from the turbine is going electric drive motor. And I think, any electric drive going on is about 4 times more efficient than the liquid fuel drive it is supplementing.

We started off this discussion saying that the laws of physics prevented this concept end of story. Now, it seems, we are having a debate about practicality, implementation, etc. I agree, its probably a dumb idea, but who knows where technology, materials, etc. will go?

I'm going to try to explain with some numbers. These are just pulled out of the air, but they illustrate the point.

Say you are losing 100 wh of energy per mile due to drag with no turbine. You put in a free spinning propeller not connected to anything, your drag might go up to around 110 wh/mi because of the drag from surfaces of the propeller blades resisting the wind. Now connect that propeller to a generator. The generator is now doing work and the propeller is going to have more trouble turning because of EM forces in the generator. Because the propeller has more difficulty turning, your drag has now gong up to 170 Wh/mi, but you're only making about 50 Wh/mi in electricity because of losses in the system. So you're net loss per mile is now 170 - 50 = 120 Wh/mi. You are now losing more energy per mile than you did with no propeller.

The actual numbers in the real world would be different, but they would always be a net loss over no turbine. There is an acronym that is applied to any system TANSTAAFL: There ain't no such thing as a free lunch.

- - - Updated - - -

The only wind turbine on a vehicle I know of is the emergency backup APU on a jet airliner. It deploys from the fuselage, spreads it's blades, and generates electricity to operate the instruments in an emergency.

So the tech exists, but it's not used normally due to the high amount of drag they create.

Yes, they are only deployed in an emergency to keep the electronics running long enough for the pilots to land the plane somewhere. The Me-163 Komet rocket fighter had a wind turbine too, but that was only to keep the electrics in the plane going when the rocket engine was shut off, which was most of the flight. Every landing in one of those was a deadstick landing. The fuel was nearly pure hydrogen peroxide mixed with liquid calcium permanganate. Really nasty stuff. Some pilots were dissolved alive by the permanganate in crashes.

Anyway, yes, wind turbines on planes are only an emergency thing deployed when everything else is dead.

 

[bxr140]

....having a turbine is not "ALWAYS" going to make something less efficient in the real world.

Incorrect. In context (a vehicle in motion), adding a turbine explicitly, unequivocally, unquestionably, mathematically, and scientifically does make it less efficient. The problem is that you are mis-applying variables to your examples. You compare a stock jeep to one with a trumpet and a turbine on it; this is a false comparison. The correct apples-to-apples comparison is a jeep with a trumpet and no turbine versus a jeep with a trumpet and turbine. In that comparison, the former will ALWAYS be more efficient. The performance of a stock jeep fascia is irrelevant to that comparison.

If you want to talk about a turbine that can be moved out of the way or a fairing to cover it or whatever else you want to do that's fine (and the answer could be different), but you can't cite those configurations so in support of your original jeep example (which is what you're doing), because they are fundamentally different.

Double finally, somebody tell me what law of physics says this does not work?

Conservation of energy. When interpreted correctly, anyway. :tongue: