I have read (and to some degree understood) that if one were to increase the number of blades for a wind turbine, it would be reasonable to reduce its rotational speed. In my mind I'd associate this with a change in transmission ratio between rotor and generator. So it would be a kind of design decision, aimed to maximize efficiency.
Now I have heard a claim which sounds stronger, namely that everything else being equal (which in my opinion includes the size and shape of the blades and the transmission ratio of the gearbox), increasing the number of blades would lead to a decrease in rotational speed. Is this true?
I find this hard to believe. I can see how increasing the number of blades would increase the amount of turbulent air each blade is passing through in the wake of its preceding blade. Due to this, each blade would contribute considerable less angular momentum, but is it really enough to over-compensate the higher number of such contributions? Am I missing some effect here? I guess drag for the whole rotor would increase, but drag per blade should be about the same.
I am not interested in problems of structural integrity which would likely result from just putting more blades on an existing design. So perhaps I should have formulated this the other way round: will removing two blades from a well-designed four-blade turbine automatically make the remaining blades rotate faster? Again disregarding the kinds of problems two-blade designs in particular do entail.
The related question Wind generators - why so few blades? discusses the number of blades in actual turbines, and its top answer compares four shorter blades against three longer ones, presumably fixing the total amount of material instead of the shape of each blade. Which probably makes sense in practice in terms of the power-to-cost ratio.