Everything Old is new again - Flettner Rotor Ship is launched

I was not saying its not a good idea. I am saying it may not be the same as a jetliner wing as you mentioned (which is tapered), and that I have never seen a test with tapered rotor. Have you?

I agree that its probably not a good idea to try and innovate here and that the fences are probably the best idea. However the concept of taper may be at least worth investigating, probably not by someone who just wants it to work right away. Certainly Stephen Thorpes tapered rotor boat worked well, but I am not sure if he tested against fenced rotors.

 

Dynamic Performance Of Flettner Rotors With And Without Thom Discs

Purely by accident I came across this specific paper on the subject

http://www.see.ed.ac.uk/~shs/Climate change/Flettner ship/TSFP7-Flettner-Rotor-Paper4.pdf

I have only glanced at it briefly, but I thought it would be good to add to the thread.

It will take quite a bit of reading to make sense of it.

After a bit of reading - this seems to be the concensus

"Thom (1934) had reported that this modification significantly increased the attainable lift coefficient
.......

The effect of adding discs at intervals along the spinning cylinder as advocated by Thom (1934) led,at low spin rates, to negligible change in lift coefficient and modestly higher drag coefficient. For spin ratios above 5,however, the lift coefficient is higher by up to 10 %. However,this is a markedly smaller improvement than reported by Thom, but the discs in his experiments were of larger diameter relative to the cylinder and with closer spacing, which may possibly account for the greater augmentation of lift. "

 

This paper shows that the computational results are under estimating drag by 4x (CDcomp=0.25 and CDexp 1.0) and lift is overestimated by 25% (CLcomp=10, CLexp=8) and this is before making allowance for induced drag. So 2D L/D is computed to be 40 where the 2D wind tunnel L/D is measured to be 8.

Any practical implementation of a rotor on a cargo ship is going to result in L/D=3 at best and more likely around 2 when accounting for finite rotor length, flow separation around the tips, interference of hull and superstructure, additional drag from leeway generated by the lateral component of force, and power required to drive the rotor.

These rotors are most effective on a broad reach (about 120 degrees course from directly into the wind). One calculation for this broad reach condition claims that it would take only 25hp to drive the rotor and get the equivalent of 270hp thrust out of it. Over optimistic but lets work with those numbers on a ship that is traveling at the same speed as the true wind. For example a freight ship using the "slow steaming" approach going 18 knots and the wind also at 18 knots.

Turn the ship to windward a bit say 60 degrees from the eye of the wind.You now have apparent wind around 30 degrees from directly ahead and much higher wind velocity. Power to drive the rotor is easily doubled and the thrust component has dropped to 10% of what it was in the broad reach. Now you have 50 hp input and are only getting 27 hp equivalent of thrust benefit. And the lateral force has become huge so the additional drag from leeway is going to be large too. So even on a close reach the Flettner rotor is a big loser and probably you can forget having any positive result on any courses nearer than 90 degrees to true wind.

Turning downwind from the optimal broad reach drops the effectiveness of the rotor very quickly also mostly resulting from the dramatically lower wind speed and rotor force vector more nearly perpendicular to the line of sail.

That gives us about 60 degrees range of course that is useful. And then only when the wind is enough but not too much.

Finally we loose it all the first time green water comes over the bow in a storm..

So your Fancy Flettner rotor is good for a 5% reduction in fuel use 15% of the time until you get caught in a storm. That comes out to less than 1% fuel savings during the time you have the rotor before the first strong winter storm.

 

So ? I don't claim to be the guru or supporter of a Flettner Rotor, I only have published reports to go on.

It could be a case of the whole of the engineering world is conspiring to defraud poor deluded fools, and all the studies are wildly optimistic and impractical.

However, I have to rely on some kind of qualified calculations and figures from people who spend a lot of money building the ships than from estimates made from personal opinion.

The Polar illustration you labelled as bogus in the other thread, came from a peer reviewed paper.

Feel free to submit your math, and any other figures you can locate.

 

And bogus it is as I have clearly shown. That paper is an example of how a claim to being "peer reviewed" can be meaningless.

 

yeah, its a real bugger when everyone else s calculations are totally wrong.

 

Or even worse when claims and theory are blindly accepted as true and passed on without critical review, but it's your freedom to graze along with the sheep if you want.

It's a mystery why so often "magic bullets" like Flettner Rotors, 100mpg carburators, snake oil, and the like are offered and people fall for the hype.

 

I have skimmed through this thread, and I realized this reminds me of the great theological debates of the middle ages. The question of which system is superior, and how many KW, or HP is produced by rotors vs. sails, vs. kites bears a great resemblence to "How many angels can dance on the head of a pin?"

 

I don't see the similarity at all. That debate was mostly over were angels corporeal or spiritual incorporeal beings.
This discussion is about physics, therefore physical concepts.

Further more it wasn't a debate between people but one man with himself.

Thomas Aquinas (c. 1224-1274), who was famous for debating metaphysical fine points.
Aquinas wrote several ponderous philosophical tomes, the most famous of which was called Summa Theologica, "summary of theology." It contained, among other things, several dozen propositions on the nature of angels, which Thomas attempted to work out by process of pure reason.
He pondered how many angels could stand on the point of a needle. Often misquoted.

 

Here is the similarity, Neither of the individuals who were the main combatants in the section of the thread I am talking about actually possesed a Flettner Rotor vessel, or even proposed to construct one for testing purposes. They were both working from secondhand reports and not from individual experiance. In essence, they were both attemptimg, through reason, to make assertions about a device with which neither of them seemed to have first hand experiance.
Granted that the modern scientific method makes the available data much more reliable, and transferable, but the passionate way in which the members in question staked out positions and defended them reminded me strongly of a theological debete. It was a matter of style, not substance.
As for Saint Thomas, and my misquote of his saying, I'm not in the habit of researching the fine points of a casual comment made in jest, and theology class was over 20 years ago for me.
Stand, Dance, Do the Macarena, Needle, Pin...Thatever. That misquote affects my point, how exactly?

 

I wasn't 'ACCUSING' you. I merely pointed out that common usage of the phrase is often mis-quoted, mis-understood, and mis-applied.

Similar to the misuse of the word decimated by our well educated leaders. They intend to convey that some radical element or force has had it's teeth pulled and no longer represents a serious threat, when they say the organization was decimated.
Decimated literally means reduced by 10%, not annihilated.
So what do words and phrases mean? Any claim to their historical definition? Or language means whatever our personal intention is at the moment, and the hearer is left guessing? Why bother talking to each other, if our language is intelligible only to ourself?

My wife had an ashtray and embedded was this phrase:

'I know you think you understood what I said. but I am unsure if you are aware, that what you heard was NOT what I meant!"

 

Stand vs. Dance....Pin vs. Needle. in what way did meaning become fuzzy with those changes?

 

All of this is off topic. Forget it.

 

When I looked at rotors I went back and used the US wind tunnel derived data from the NACA archive (now freely available on the NASA website).

The wind tunnel tests showed, very clearly, that there was a pretty high L/D ratio over a wide range of operating conditions, with L being pretty much proportional to rotor peripheral speed vs wind speed, and drag varying a lot less. I produced a spreadsheet from this US NACA test data (it's buried somewhere earlier in this thread) but the hard data does show that rotors have a far better L/D than sails.

There are some quirks, as Stephen Thorpe re-iterated with his experimental rotor driven boat. The performance with a slim rotor was about the same as that with a very much larger sail, but the way the rotor creates lift at 90 deg to the relative wind produces some undesirable effects, like a high roll moment when the wind is directly ahead or astern, and no lift under those conditions, just drag.

Nevertheless, as rotor power is determined primarily by frictional losses in the drive system, and is effectively unrelated to the wind conditions, there is scope to do further work on the concept.

Will it have applications on cargo carrying craft? I don't know, but I doubt it, due to the many constraints it places on deck handling and manoeuvrability.

Does it have applications on leisure craft? Probably, provided the requirements can handle the peculiarities of the drive system.

As a drive system I think it is probably better than sails (less space taken up, no need to reef, less wear and tear, simpler handling and better L/D). It suffers from some limitations, though, like the need to tack downwind as well as upwind, and the rotor speed and direction control needed to safely tack or gybe without fear of capsize from the high roll moment as you come through the eye of the wind.

 

In addition to all the good info you guys have provided, I would like to add that a Flettner rotor also has a stabilizing effect on the ship's roll, because it acts as a gyroscope. Without bothering you with the math, it essentially transforms the roll accelerations (around the longitudinal ship axis) into a rotation around the transverse axis. But the ship behaves in a pretty stiff manner around the transverse axis, so the resulting pitching motion is very small.
This anti-roll moment also induces additional loads to the structure of both the rotor and its supports. These have to be accounted for in the scantling of the structure.