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  #106  
Old 09-02-2010, 04:46 PM
Clarkey Clarkey is offline
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Originally Posted by tspeer View Post
Neither Cousteau's catamaran, Moulin a Vent, nor Alcyone used a Flettner rotor or anything like it. The Alcyone used a turbosail, which had a fixed cylinder and a flap with sharp trailing edge that could be positioned at any point around the cylinder. It used boundary layer suction to avoid separation on the cylinder. This is an entirely different principle of operation from the Flettner rotor. It is essentially a conventional wing with a very large thickness ratio. It has more in common with a Griffith airfoil than a Flettner rotor.

The Flettner rotor sounds great when you see the large lift coefficients. But the problem is the rotor produces a lot of drag. And sailing performance depends on the lift/drag ratio. Take a look at Figure 5 from NACA-TN-228, "The Flettner rotor ship in the light of the Kutta-Joukowski theory and of experimental results". The rotor can produce a section lift coefficient of 9, but has a minimum drag coefficient of 0.5! The maximum sectional lift/drag ratio is less than 8, which is an order of magnitude less than for a wing section. You can make the wing 10 times bigger and still have less drag, and the benefit of the large lift coefficients vanishes.

The paper claims a much reduced heeling moment from the shorter rotors, but that doesn't account for the impact on induced drag. The induced drag depends on the square of the span for a rotor, just like a non-rotating wing. So if the span reduced considerably - almost a must for practical reasons with the rotating machinery - then the induced drag skyrockets.

The Flettner rotor has one big advantage as a sail: you can turn it off. The maximum lift at a given rotor rpm increases with wind speed, then flattens out and does not increase appreciably for higher winds. So in a blow, the ship can regulate the maximum force by controlling the rpm. The other advantage of a rotor is it doesn't obstruct much deck space, compared to the sweep of a boom.

The turbosail would share many of these advantages, as the additional sweep of the turbosail trailing edge is not great and the boundary layer control can be turned off to stall the rig. But it would have high windage compared to a feathered wingmast. And it would incur the induced drag penalty of using a smaller span than a conventional rig if made to the same proportions as Alcyone.
Absolutely, the Flettner rotor is not a high performance sail, it is an interesting curio with some handling advantages that may, one day, find it a niche somewhere. Or not.

Just out of interest, how does a l:d of 8:1 compare with a typical cruising soft rig?
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  #107  
Old 09-02-2010, 05:06 PM
apex1
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Originally Posted by Clarkey View Post
Absolutely, the Flettner rotor is not a high performance sail, it is an interesting curio with some handling advantages that may, one day, find it a niche somewhere. Or not.
Hmm, the question if high performance or not might be discutable. But ten times the thrust than a textile sail of smilar area is at least a good result, no doubt.

The "Buckau" btw. had only a 10hp El. motor to provide the rotation! (per Rotor)

tspeer,
Alcyones "turbovoile" is a knockoff of the Flettner system without the rotation. Here the boundary layer suction is used, but the efficiency is about 20 -25% below the original system.
Calypso II was planned with a real Flettner Rotor (as shown in the picture I posted above) due to better performance. It was not realized after Cousteaus death.

The statement that E-Ship 1 is not performing is nonsense! Enercon reports fuel savngs between 30 and 40% at 16kn! I call that success.

Now we define success?

Regards
Richard
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  #108  
Old 09-02-2010, 05:13 PM
Clarkey Clarkey is offline
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Originally Posted by apex1 View Post
Hmm, the question if high performance or not might be discutable. But ten times the thrust than a textile sail of smilar area is at least a good result, no doubt.

The "Buckau" btw. had only a 10hp El. motor to provide the rotation! (per Rotor)

tspeer,
Alcyones "turbovoile" is a knockoff of the Flettner system without the rotation. Here the boundary layer suction is used, but the efficiency is about 20 -25% below the original system.
Calypso II was planned with a real Flettner Rotor (as shown in the picture I posted above) due to better performance. It was not realized after Cousteaus death.

The statement that E-Ship 1 is not performing is nonsense! Enercon reports fuel savngs between 30 and 40% at 16kn! I call that success.

Now we define success?

Regards
Richard
Well indeed, maybe the niche is cargo ships which need a compact rig which doesn't get in the way during loading and has simple push-button control from the bridge?

Where did you find the Enercon reports? I would love to have a look at them.
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  #109  
Old 09-02-2010, 05:25 PM
apex1
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Originally Posted by Clarkey View Post
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Well indeed, maybe the niche is cargo ships which need a compact rig which doesn't get in the way during loading and has simple push-button control from the bridge?
Ore carriers and tankers, as I mentioned two times now, don´t have that problem. And of course it is a simple push button control, what else.

Quote:
Where did you find the Enercon reports?
In recent conversations with the management of Enercon. They will be published soon I was told.
This is the official report, released after the last test drive which confirms that results are in accordance with the estimations (which have been 30% to 40%).

Aurich, 29.07.2010


E-Ship 1 zurück in Emden

Nachdem die Arbeiten bei der Lloyd-Werft in Bremerhaven termingerecht abgeschlossen wurden und das E-Ship 1 auch seine dritte Probefahrt erfolgreich absolviert hat, liegt das Schiff nun wieder in Emden, um dort in den nächsten Tagen ladeklar gemacht zu werden und Windenergieanlagenkomponenten für die erste Transportreise aufzunehmen. Aufgrund der Testfahrten lässt sich feststellen, dass die Technologie des E-Ships funktioniert. Genaue Ergebnisse teilt ENERCON nach Abschluss der gesamten Versuchsreihe und Auswertung der Daten mit.

ENERCON GmbH
- Marketing / PR -
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  #110  
Old 09-02-2010, 08:13 PM
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rwatson rwatson is offline
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Originally Posted by philSweet View Post
The strangest thing to me is that after five hours of looking, I couldn't find 1 single data point on a Fletner Rotor test that provided the minimum data needed to make an engineering decision. As a minimum one needs-
Rotor geometry
Rotor speed
Wind speed
Magnus force
Drag force
Applied power
Any comparisons with other forms of propulsion need to be done in terms of work (or power), not forces. This has led to a lot of confusion so far with respect to sailboat comparisons. You cannot use lift-to-drag ratio in any meaningful way with respect to Fletner rotors. These are forces. You must use energy. .
for wind force, drag and lift co-efficients refer to calcsl02.jpg and calcs03.jpg
as posted in post 52. I see some other contributions have also provided usefull data.

For effort on rotors, refer to Joseph Norwoods publications as the best source, though there is reputadely heaps of Flettner calcs in "paper" libraries in other locations.

Just because its not on the Net doesnt mean to say it doesnt exist.
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  #111  
Old 09-03-2010, 01:17 AM
tspeer tspeer is offline
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Originally Posted by apex1 View Post
Alcyones "turbovoile" is a knockoff of the Flettner system without the rotation. Here the boundary layer suction is used, but the efficiency is about 20 -25% below the original system.
I can see how one would confuse the two if one went soley by visual appearance and didn't understand how they actually operate. But other than the fact that they both generate lift and have circular arc contours, they work completely differently. Saying the turbosail is a knockoff of the Flettner rotor is like saying a turbine engine is a knockoff of a reciprocating engine, but without the pistons. Take away rotation from the Flettner rotor, and you eliminate the whole point of the concept - it's no longer a rotor.

As has been pointed out earlier in the thread, the Flettner rotor is completely axisymmetric and operates in the same way regardless of the apparent wind direction. The amount of circulation is determined by the locations where the air separates.

Boundary layer control is achieved through rotation speed. Because of the no-slip condition at the rotor wall, there is less shear in the boundary layer on the lee side, as the wall is moving in the same direction as the flow outside the boundary layer and the difference in speed between the wall and outer flow is reduced or even reversed (faster at the wall than in the freestream). On the windward side, the shear is increased, due to the wall moving in the opposite direction to the ambient flow. So separation is delayed on the lee side and separation occurs earlier on the windward side. The asymmetry of the separated flow results in circulation about the cylinder and lift on the rig. The faster the rotation speed, the more the asymmetry.

The turbosail has a sharp trailing edge that fixes the lift using a Kutta condition like a conventional wing Ideally, the flow would come off smoothly from the trailing edge and there would be no separation anywhere. The trailing edge has to be positioned relative to the apparent wind direction, just like the trailing edge of a wing. If the trailing edge were allowed to float, there would be no lift on the rig. In this video of a wind tunnel test of the turbosail, the cross section shape of the turbosail isn't even round - it has a circular trailing edge and is stretched toward the leading edge, flattening the sides.

Boundary layer control is achieved through suction on the lee side. The purpose of boundary layer control on the turbosail is to avoid separation altogether. The lift is determined by the flap position and the angle of attack, just as it is with a conventional wing.
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  #112  
Old 09-03-2010, 02:26 AM
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thudpucker thudpucker is offline
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I'm still confused.
I recall the 1980 announcment. I thougt it was odd that a small windfoil like that stack could equal a large wind foil like a sail.

So is that stack driven by an engine, or is it driven by the wind going by that stack?
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  #113  
Old 09-03-2010, 04:35 AM
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troy2000 troy2000 is offline
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Originally Posted by thudpucker View Post
I'm still confused.
I recall the 1980 announcment. I thougt it was odd that a small windfoil like that stack could equal a large wind foil like a sail.

So is that stack driven by an engine, or is it driven by the wind going by that stack?
Hard to understand how you could ask that question if you had read the entire thread, so I'll have to assume you didn't...


The rotor is turned by a relatively small engine or motor of some sort. It only has to be large enough to keep the rotor spinning; the assymetrical airflow of the wind around the spinning rotor is what creates the driving force.
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  #114  
Old 09-03-2010, 06:35 AM
apex1
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Originally Posted by tspeer View Post
I can see how one would confuse the two if one went soley by visual appearance and didn't understand how they actually operate. But other than the fact that they both generate lift and have circular arc contours, they work completely differently. .
Well, that is a bit mute to discuss due to the fact, that the turbovoilee is not efficient enough to be noticed. And Cousteau therefore went for a original Rotor for Calypso II.

But the Technical University Flensburg, where one of the recent test boats has being developed and built:



did see the turbovoilee that way.

The Uni Kat btw drives the Rotor by a simple solar cell of a few watt only.

Regards
Richard
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  #115  
Old 09-03-2010, 10:58 AM
Clarkey Clarkey is offline
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Originally Posted by apex1 View Post
Well, that is a bit mute to discuss due to the fact, that the turbovoilee is not efficient enough to be noticed. And Cousteau therefore went for a original Rotor for Calypso II.

But the Technical University Flensburg, where one of the recent test boats has being developed and built:



did see the turbovoilee that way.

The Uni Kat btw drives the Rotor by a simple solar cell of a few watt only.

Regards
Richard
Calypso 2 was designed to have a Turbosail - not a Flettner rotor:
http://www.cousteau.org/about-us/calypso2


I would love to see some performance data for Unikat - I haven't been able to find anything much on the web and all the photos seem to show it travelling at a fairly sedate pace.
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  #116  
Old 09-03-2010, 11:02 AM
Clarkey Clarkey is offline
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Originally Posted by troy2000 View Post
Hard to understand how you could ask that question if you had read the entire thread, so I'll have to assume you didn't...


The rotor is turned by a relatively small engine or motor of some sort. It only has to be large enough to keep the rotor spinning; the assymetrical airflow of the wind around the spinning rotor is what creates the driving force.
I presumed that Mr. Thudpucker was asking how the Turbosail on the Cousteau society ship 'Alcyone' worked - it has an electrically driven fan at the top of each cylinder which sucks air in through one or other of the grills running down the side.

The turbosail has always struck me as almost the worst of all possible worlds.
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  #117  
Old 09-03-2010, 11:22 AM
apex1
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Calypso 2 was designed to have a Turbosail - not a Flettner rotor:
That is wrong! They are just too dumb to translate right.

The design sketch I posted above (a page or two back), shows the original design in a sketch done by the NA.

Cousteau was well aware that the turbosail was crap.
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  #118  
Old 09-03-2010, 11:45 AM
Clarkey Clarkey is offline
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Originally Posted by apex1 View Post
That is wrong! They are just too dumb to translate right.

The design sketch I posted above (a page or two back), shows the original design in a sketch done by the NA.

Cousteau was well aware that the turbosail was crap.
Does that look like a rotor or a turbosail in the picture to you?

Even if it was crap I get the impression that Cousteau's ego would have demanded that they continue with it anyway. Crew accounts seem to say that the turbosails were noisy, not wildly effective and often not used on Alcyone.
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  #119  
Old 09-03-2010, 12:23 PM
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philSweet philSweet is online now
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for the sailors out there, a #4 headsail?
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Everything Old is new again - Flettner Rotor Ship is launched-flettner0001.jpg  
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  #120  
Old 09-03-2010, 12:31 PM
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thudpucker thudpucker is offline
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What I didn't understand was the Energy it took (the Diesel motor) to drive whatever was inside the big smoke stack, must have been more expensive and more complex than plain old sails.
It surely would be more productive driving a shaft with a prop, rather than driving air across an air foil.
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