Everything Old is new again - Flettner Rotor Ship is launched

I'm reasonably sure that if you stay within the u/V ratios that have been validated then the Cl and Cd formulae I used will give a pretty good approximation. The problem arises if you go outside that range, i.e. u/V of greater than about 4.5.

In practice I'm not sure that this is a particular issue. I'm reasonably convinced that Cd can still be predicted reasonably accurately for u/V values of greater than 4.5 by using the formula in that spreadsheet, but less convinced that Cl can be. Instinctively I'm inclined to believe that Cl may have a fairly linear relationship to u/V above about 3.5, probably something like this: Cl = 0.4346(u/V) - 0.6472

 

Jeremy, I do not believe u/v ratios are meaningful. It is simply not a relevant nondimensional parameter for the actual problem at hand. The lift of a Flettner rotor is due to the thing that isn't rotating - the separation bubble - not the thing that is rotating. Thus u/v is a figment as far as engineering a rotor is concerned. It's what you get when you force an analogy to wing maths by adopting Re, Mach as starting points, but like I've already said, I don't believe it is useful to look at them as wings. They need their own set of metrics and those will be different from the ones that turned out to be convenient for engineering wings. Not that I have any set to offer up, although rotor diameter/viscosity would be one I would look at.

Since the biggest problem seems to be getting past the not-a-wing idea, let me try this -

1. Take any extruded shape you like and call it a wing section and place it in a uniform windfield. Now rotate the wing slowly at constant rpm about any axis parallel to the extrusion. Slowly means that the windspeed near the surface of the wing is nearly the same as the free stream, ie apparent wind effects are negligible. What is the C_l integrated over one rotation?

2. Why can't a Darrieus wind turbine rotor be designed to self start from any and all angles?

3. Go back to 1. and replace the slowly criteria with one of bilateral section symmetry. You now have a sort of random Darrieus rotor with inside/outside blade symmetry.

4. What is the average sideforce on the base of a Darrieus rotor. That would be analagous to a Magnus force, wouldn't it?

A Flettner rotor is more like a Darrieus working in the first quadrant (powered instead of braked) than a wing. Except that we can actually model a Darrieus device with some confidence since they have been made out of wings. Power it instead of brake it, and measure the base loads and force vectors. My conjecture is that even with big apparent wind effects, the net side force on a base support will average out to zero using first order effects. You just plain can't get a lift force out of a steadily rotating wing. As far as I can tell, it always time averages to zero.

So the question in my mind is what are we actually doing with the power that is being injected into a Flettner rotor, because the part being used to rotate the darn thing is being wasted! If we want to mess with the boundary layer, just pump the air in there where we want it. How could spinning the rotor possibly be more efficient than ducting the air directly to create the separation bubble and jiggle the stagnation points? Calculating the power needed to maintain a particular bubble by direct injection should be a scalable in a normal fashion.

Sorry if the tone is provocative. I'm trying to understand the things too. The whole of the above is conjecture.

 

Well, technically a Darrieus can self-start, it just can't accelerate through a
"dip" at tipspeed ratio = 1.
The tipspeed ratio (TSR) is R*omega/U, where R= radius, omega is rotational
speed in rad/sec, and U is wind speed.

Quite a few people have died because they assumed that these turbines
cannot self-start. Wind direction changes can get the turbine through the
"dip"; the turbine then accelerates to 3 or 4 times the speed of the wind.
Wings have hit people and/or knocked them down from a height with dire
consequences.

 

I'm afraid I disagree, as the wind tunnel test data shows very clearly indeed that Cl and Cd are proportional to u/V. It's given in the NACA wind tunnel test data in NACA Technical Note 209, "Tests on rotating cylinders" by Elliott G Reid, Langley Memorial Aeronautical Laboratory (copy here: http://www.boatdesign.net/forums/at...hnical-note-209-tests-rotating-cyclinders.pdf).

Also, practical experience from those who have made rotor powered boats (like Stephen Thorpe, whose boat is described earlier in this thread) also confirms that lift is proportional to u/V; speed up the rotor in any given wind and the boat goes faster, slow down the rotor and the boat slows down. Stephen wrote this about his own experimental rotor powered boat:

"There is a clear and strong relationship between rotor speed and boat speed in any given wind, but the subtler question of which rotor speed is most efficient in terms of speed for power consumption in any given wind, is beyond me as yet."

The above was taken from Stephen's article, reprinted earlier in this thread here: http://www.boatdesign.net/forums/bo...-rotor-ship-launched-24081-10.html#post396581

A photo of his boat can be seen in this page from the AYRS: http://www.ayrs.org/flettner.pdf

 

Chart with Ship Wind to Propulsion Vectors

I think its sorted now.

This version has a ship performance vector calculator. The chart uses the calculated Cl/Cd in Jeremys chart.

 

After a long silence, here is the official news on E-Ship 1:
http://www.enercon.de/p/downloads/PM_E-Ship1_Ergebnisse_DBU_en.pdf

"Using the Magnus Effect, the four innovative Flettner rotors provide the main engine with additional drive and account for more than 15 percent of the savings."

Pierre-Yves

 

Well spotted Pierre

"Since its maiden voyage in 2010, the „E-Ship 1“, developed for transporting ENERCON wind turbine components, has covered more than 170,000 sea miles – primarily in the North and Baltic Sea, North and South Atlantic Ocean and the Mediterranean Sea."

"the four innovative Flettner rotors provide the main engine with additional drive and account for more than 15 percent of the savings. "


"if a supertanker were to be equipped with the „E-Ship 1“ technology, it would be possible to save up to 9,000 tons of fuel (approx. 27,000 tons CO²),
which adds up to roughly 5 million dollars per year....
It is really impressive to see just how successful ENERCON-developed systems for reducing energy consumption in commercial transport vessels have proven to be,“ says ENERCON Managing Director, Nicole Fritsch-Nehring. ENERCON intends to maintain this technology and continue investing in further development work. As soon as the current retrofi tting work on the „E-Ship 1“ has been completed, the vessel will again be sailing the seven seas delivering ENERCON wind energy converters"

At least its not being scrapped. It sounds like they are going to try to market the concept.

 

Any interest in re-energizing this old thread?
I have two Albin 25s. One has conventional jib and main.
I'm considering a different rig for the 2nd hull.
This might be a chance to try the Flettner against an identical boat.

 

I would be prepared to contribute a small amount to the final cost to encourage you to try it. I wonder if a bit of crowd funding would help ?

I think that using modern composites would solve a few practical issues like vibration.

I emailed a carbon spar engineer a while back to see if he thought he could design a cylinder that would stay intact, and he estimated about AU$3000 for the engineering calcs. Maybe a good welder could put together an aluminium space frame tower.

It would be a weird feeling to feel the boat lean slightly into a reaching wind.

Let us know how you progress with the concept.

 

That's a generous offer, but I decline with thanks.
I'm far from rich, but I prefer to pay for my own boat.
I'm looking for ease of handling rather than speed.
My wife isn't much of a deckhand. I can still scamper about pretty well, but that isn't forever.
For a 25 ft 4000 lb boat, how big would you expect the cylinder need to be? Low aspect preferable though this Albin 25 design has enormous stability without lead ballast.
I'm not anti-velocity. I like motor sailing because of the synergy of the systems. If this apparatus added a knot or two to my motoring speed, it's of intrinsic value.

 

The required motive power should be easy to calculate.

I cant remember where its located, but if you can provide the sail area on you boat, we can look up how much the maximum driving force you would expect to get.

Once we know that, it is a fairly easy job to pick an appropriate diameter and rotational speed to get to that target + say 10% for good effect.

The diameter of the rotor can also be chosen to suit your deck size to a certain extent.

The biggest headache will be to engineer the support structure, which is where an engineer will come in handy.

Do you have mast pillars on the boat or are the masts keel stepped?

 

I think this is interesting as possible drive to spin Flettner drum.

https://www.youtube.com/watch?v=t2KJnT5jQng

 

Sail plan.
Mast stepped on cabin top with stainless post beneath in cabin.
I have been thinking tripod mast on 2nd boat.

Maybe Flettner could revolve inside tripod?
Keeping the mast allows light air sails the Flettner won't operate in.

 

Has anybody tried flying a jib with a Flettner drum for slot effect?

 

http://upload.wikimedia.org/wikiped...n-Wannsee,_Rotor-Yacht_mit_Flettner-Rotor.jpg

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