Analysis of separated flows in hydro machines

Separated flows around airfoils, in pumps, and in hydraulic turbines are discussed with the aim to understand the mechanism. Stall is defined as flow separation without reattachment to blades. The modified Kutta-Joukowskij condition is explained by Karman vortex rows. For rotating stall in pumps the classical explanation is repeated. A theoretical explanation is shown that rotating stall may be expected in hydraulic turbines as well. Rotating stall seems to cause spiral-form vortex ropes in Francis draft tubes. For spiral ropes the precession theory is also mentioned. Kaplan draft tubes are exempt of this problem because stall is likely not present. Future research is needed to sort out the interconnections of the rotating stall theory and the precession theory.