Everything Old is new again - Flettner Rotor Ship is launched

I'd recommend a bit 'out of the box' thinking. The very thing that ticks the Flettner is the circulation around it, not the rotation of the rotor itself. Thou MD might had a patent for that..

 

I have done lots of searching and I came across many ways of estimating the power, but in every single one of them I am missing data (most of them being dimensions) that I do not have any approximate figures. I guess lack of real life ship experience is showing up. And the thing is that I do not have time to get into more detail since I have one month left and my main purpose is to focus on exhaust gas turbine producing the power needed.
Also, I am using the case study of E Ship 1, but Enercon has not given any data to the public and would not reply to my emails.

Do you think there is a way for a decent estimate without getting into much details?

I have attached a pdf file of a part of my Power Estimation, for which I am using an equation that I found on the internet but I am not sure if I can use it. (the Mf equation)

So you mean that the wind drag should be the one impacting more on the power needed to rotate rather than the power to keep the cylinder rotating?

Thank you all for your attention and help

 

For small rotors the losses are mainly friction in the bearings and drive system, as the viscous drag from the air moving past the surface of the cylinder is pretty small.

You can work out the viscous drag from first principles easily enough, using just the peripheral velocity of the rotor, the rotor rpm, the rotor diameter/length and the density and viscosity of the air. In essence the calculation is the same as for the hull resistance of a low speed boat, where viscous drag dominates.

I practice the rotor drive needs to be significantly over powered in order to give fairly good acceleration (and deceleration if you want to actively control the strong roll moment as the boat tacks or gybes). If it were me I'd ignore the viscous drag calculations and just design for enough power to give the required rapid rotor rpm and direction change, which is primarily a function of the rotor rotational inertia.

 

That is a really good idea.
I had in mind that I shall increase the power needed for acceleration, but this makes more sense now.

So I can calculate the power needed assuming that there is the need to reach 50rpm in 1 minute.

Another useful information I have obtained from a video (in German) is that the material used on E Ship 1 is steel for the runner, and the cylinder itself is half steel (inner side) and the other half aluminium, while the runner is located 10 meters below the upper end of the cylinder.

What do you think about the assumed figures above? My concerns are on the actual time needed in real life to decelerate the rotors for safety reasons.

Thanks a lot.

 

A 1 minute response time is perhaps a bit on the slow side, unless this is a large ship. Bear in mind that if the wind shifts to either ahead or astern the rotor will produce a large roll moment, as the thrust vector then goes to directly abeam. You need to be able to slow and stop the rotor as the ship tacks or gybes and then change it's rotation direction and get it back up to speed on the new tack.

This means that the rotor speed and direction response time has to be matched to the boat or ship helm response, so that you can't get the situation in high winds where the boat turns faster than the rotor can slow down, stop and change direction.

The lighter you can make the rotors, or more specifically the lower you can get the rotational inertia, the better, as it's this that determines how much power you need to be able to accelerate and decelerate them within the required time.

 

The dimensions are fixed since I am working on the E Ship 1. So the rotors are 27m high and of 4m diameter.

I ll try several calculations on 20-40 seconds since it is not feasible to calculate the appropriate time needed for the rolling phenomenon you described and I will end up using the one that makes more sense by that time.

 

The rolling problem is serious, as if the boat turns so that the wind is ahead or astern with the rotors turning at full speed then the full thrust that the rotors can develop becomes a rolling force, trying to capsize the boat.

If the rotor cannot be stopped quickly, then a capsize is possible. The worst condition is probably something akin to a broach in a conventional sailing boat (and Flettner rotor
boats are sailing boats). This can be a rapid event, even in a fairly big boat, so there needs to be a means to at least stop the rotor quickly. Ideally that system should be able to slow and reverse the rotor at a rate that keeps the thrust vector pointing in the right direction at all times.

 

Dont forget though, that unlike normal sails, the majority the 'pressure' is lift.

The actual pressure on the rotor, spinning or still, from the profile of of the cylinder (drag) is quite small.

In other words, trying to broach the boat by not slacking the mainsail in time, is not as great a problem in a Flettner setup

 

It is the high rotor L/D, though, together with the relatively slow rotor response time, that causes the potential problem.

The more or less exact equivalent of slacking off the sheet to depower the rig with a rotor is to stop it spinning. As soon as the rotor stops the lift stops. Unlike just letting go of the sheets on a conventional sail, which is pretty much instant in effect, slowing the rotor takes time, in the case of a big rotor many tens of seconds.

Lift from a Flettner rotor is proportional to rpm, so if the rotor is spinning when the wind comes either abaft or ahead there can be a significant problem, if the lift cannot be killed by stopping the rotor..

 

Power assist disc brakes?

 

These folks make strong claims of power generation from their wind turbine with Flettner rotors.
http://www.engineeringtv.com/video/Spiral-Magnus-Wind-Turbine

 

Looks impressive. More efficient, quieter, but more expensive than conventional windmill

More history and info here

http://www.mecaro.jp/eng/introduction.html

 

I believe it can be dangerous too when it comes to great L/D ratio and even if it is not dangerous, it is something causing instability of the ship.

So Flettner rotors are operating in a favorable angle interval but they should be able to stop fast when needed.

But the disc brakes also sound as a nice solution for sudden changes in the wind direction. I wonder whether they are already in use.

 

All commercial Flettner rotors had braking systems.

From accounts I have read, unlike sails, sudden wind changes are not a big issue. There are no 'chinese gybes' or overpowering gusts to watch out for.

You don't have to 'trim' the rotors as you do sails, as they are totally symmetrical cylinders, and the lift vectors just change as the wind varies direction. The rotation rate is easy to control

 

Sure, I guess a sudden powerful wind coming from the back is not very common either but it should be a factor kept in mind when designing meticulously the rotors at the final stage.

So decelerating the rotors should be easy, the hard part is accelerating from 0 to the desired speed, since this is when the friction and the viscous drag will have an opposite effect to the rotation.
Unless this losses can be considered very low compared to the power needed to move the whole rotor from being still.

Of course even if accelerating takes a longer time it is not going to be dangerous, it would just lead to less fuel savings since there would be a lag before actually utilizing the wind.