Flettner Rotor Sails Again?

[PierreB]

@batlabat

I see more relationship with suction sail (already discussed here Suction Sails ) than rotor.

An example is given with Turbosail from Jacques-Yves Cousteau:

Co-Flow Jets

Turbosail uses a similar principle: Concerning CFJ, improving CL would be interesting for AWE if CD is not too high, even if a very high L/D ratio is not required because the tether drag would flatten this ratio. For the rest, efficiency issues still affect the AWE sector until solutions emerge.

@batlabat

I don’t really trust results when I see negative Cd without a power coefficient given, it is meaningless.

I think you allude to a quote of a referenced paper:

@PierreB

Figure 6 shows all the airfoils generate thrust (negative drag) in the
wind tunnel testing

It seems that both suction sails and above all Flettner rotors are starting to be implemented in the maritime domain.

For an AWE use, Flettner rotors like Omnidea’s balloon look to be easier to implement because a cylindrical shape is easy to obtain with a light inflatable balloon. And drop-stitch and similar technologies could (?) allow to stiffen the balloon and save energy consumption.