I definitely think we're on the same page, and think you might be right; we're talking about the same thing... But there is a lot of imprecision out there when it comes to explaining the mechanism of agreed-upon phenomena, so I always find it interesting to try to come to understanding of the actual effect at work. I will definitely have to learn more about the centrifugal force in this situation; thanks for the steer on the word "gating". But leaving that aside for a moment (let's say we come up with a method that will negate that effect entirely), wouldn't you think there will still be an efficiency drop as the linear speed of the turbine approaches the speed of the stream driving it? So, assume there is no disruption of the corkscrew at all--- won't we still have efficiency drop as an expected result of the speed differential approaching zero?
I actually found out about Tesla turbines because of work I've been doing on vortex phenomena of all types; it seems like vorticies are one of those (I think of them as 'magic') areas of science where you get a synergistic payoff from what goes in... Of course, there's no such thing as a free lunch, but some things (like latent heat, for example) really seem to have potential benefits that in some way 'go beyond' what you might expect.
I wouldn't be suprised if the 'corkscrew' or vortex effect in the Tesla turbine is an important (if not indeed critical) component of how it functions in the first place.