Effects of operating condition on fish behavior and fish injury in an axial pump

In this study, fish behavior and fish injury at different operating conditions are investigated via numerical simulation to evaluate the fish-friendliness of an axial pump that comprises an inlet pipe, a rotor with six blades, a stator with eight vanes, and an outlet pipe. To precisely obtain the flow field when the fish passes through the axial pump, a hybrid large eddy simulation and immersed boundary method is adopted with the full consideration of the fluid-structure interaction comprehensively. The results indicate that the collision between the fish and the wall of flow components in the axial pump is concentrated near the inlet of the rotor, which results in the complexity of the fish trajectory, especially under the large flow rate condition. It is noted that the fish is likely to move in the reverse direction of the main flow after the impact with the rotor blade if the flow rate coefficient is too large, which increases the possibility of collision between the fish and the rotor blade. It is also indicated that the primary factor affecting the strike injury on the fish when it passes through the axial pump is the strike between the fish and the leading edge of the rotor blade. In addition, the strike injury becomes more significant as the flow rate coefficient increases. Furthermore, the results demonstrate that the fish may simultaneously suffer from strike, pressure, and shear stress injuries, once the collision between the fish and the wall of flow components occurs in the axial pump, thus aggravating the combined damage on the fish. Based on these results, it is recommended that hydraulic machinery should not be operated at large flow rates during fish migration from the view of fish-friendliness.