Hi Peter,
I’m a bit uncertain, but I suspect that when you increase the size of your solution space (by increasing the bounds on rotor speed), the GA is less effective because it takes either more time or larger populations to converge. When you increase OmgMax, I bet a larger percentage of each population violates the cavitation constraint…which implies the “death penalty” described above. If there is an excessive amount of constraint violations within each generation, the GA will probably converge prematurely. In summary, I would try setting tighter bounds on the rotor speed to avoid cavitation and its negative effects on efficiency.
All the best,
Danny