Draft Tube Design Method for Operation at optimal Coefficient of Performance in Low Head Hydropower

Commonly practised design methods for low head hydropower draft tubes are aiming to minimize dissipative losses, hence to maximize hydraulic e ciency. Betz established the coe cient of performance for wind turbines. It is a more general view on e ciency, since it not only takes dissipative losses into account, but also nondissipative losses, due to wake energy ux. The second author derived the coe cient of performance for an open channelow in analogy to Betz. The present paper presents a new approach for operation at optimal coe cient of performance.