Abstract: A turbine 400 has a central duct 410 which accelerates fluid passing through it and a blade configuration which retards the flow of fluid near the tips of the turbine. This structure results in a vortex having a higher fluid pressure behind the tips of the turbine blades 408 and a lower fluid pressure behind the duct. In the present invention, this vortex is enhanced by (1) an increased acceleration of the fluid passing through the duct 410 and a deceleration of the fluid passing through the blades 408; and/or (2) by a fluid redirection device 850 for directing the fluid passing through the duct towards the outer diameter of the turbine.