Solar Aero's Howard Fuller says the principal of operation is roughly the same as for the Tesla steam turbine.
"Closely-spaced discs trap the motive fluid molecules (in this case air) in a laminar flow adjacent to the disc surface. This provides aerodynamic drag, which imparts force to the disc surface. By using multiple discs, the turbine then provides considerable torque to accelerate the rotation of the central driveshaft, which is directly coupled to an alternator, typically located at the base of a tower, or alternatively co-located on a rooftop."
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