By turbine I understand the structure with blades; for wind turbines, the blades are long and slender but for water turbines they are small and heavy. The design for high temp gas turbines are complicated but they still have a very large number of vanes (half of them are stationary). A well designed generator can have high efficiency at the design RPM; but I am not so sure about the wind and water turbines. Gas turbines, I am told, approach very high efficiencies (about or above 50% of the Carnot efficiency), that just means that lots of energy is released with the exhaust gases.
I thought the OP wanted the electrical core design (the stator; that contains the coils) and I did not get the impression that he wants to design the turbine blades. I am still not sure the power level he is interested because the design strongly depends on the power level begins considered.