Fish injury analysis and flip-blade type optimization design of an undershot waterwheel

In this study, the performance of the ultra-low head undershot fixed-blade and flip-blade waterwheels are studied via numerical simulations to evaluate their efficiency and stability. On the other hand, the accuracy of the numerical simulation of the fixed-blade waterwheel is verified by field tests before the flip-blade waterwheel is designed on its basis. Moreover, the likelihood of fish injury in the fixed-blade waterwheel is predicted to evaluate the fish-friendliness of the waterwheel. Applying the overset grid algorithm, the results indicate that the fish is most vulnerable to damage in the rotor area and that the fish suffer some impact damage but almost no pressure and shear stress damage, and a minimal probability of mortality present, confirming that the waterwheel is fish friendly. Furthermore, the power coefficient of the waterwheel with the rise of tip speed ratio tends to increase first and then decrease, while maintaining a positive correlation with the immersion depth within a certain range. Additionally, flip-blade owns higher efficiency than fixed-blade waterwheel under the same working conditions but is slightly less stable. We expect that these results will help establish design guidelines for more efficient flip-blade waterwheels to break the impression that traditional undershot waterwheels are less efficient.