# Optimal Design and Fish-Passing Performance Analysis of a Fish-Friendly Axial Flow Pump
## 5 Fish-Passing Performance Analysis of the Fish-Friendly Axial Flow Pump  
### Analysis of the Behavior Trajectory of Fish through the Axial Flow Pump  
For the modeling of real fish, the balance between the simplification of the model and the calculation effect should be considered. First of all, the connection gaps of fins, tails, and organs on the surface of fish bodies should be ignored. Secondly, the fish body model should be convenient for computer recognition and calculation, that is, the complexity of the surface modeling of the fish body should be simplified, and the modeling of the fish body should be based on the surface composed of a simple conic curve.  
According to the above modeling requirements, this paper established a fish body model with a 150 mm body length and other fish body models with only tail and belly shapes. Through trial calculation, it was found that the computational efficiency of the OB fish was lower than that of the SP fish under the lattice model, which could restore the best analytical scale of the fish's surface shape. The effects of the two forms on the flow field and fish surface calculation results were not obvious. Therefore, the SP fish with a higher computational efficiency was selected as the fish body model object for subsequent calculations in this paper.  
After entering the channel, the fish passed through the inlet channel, runner, guide vane, outlet channel, and other areas one by one. Due to the continuous work done by the pump blade, the kinetic energy of the flow body increased sharply, which made the movement trend of fish very easily affected by the fluid in the pump. Therefore, the change in the flow field characteristics caused by the change in the pump structure was bound to affect the trajectory of the fish. This section combines the LES-IB-LBM method to explore the influence of the change in flow field characteristics on the passage of fish.  
When simulating the fish body passing through the fish-friendly axial flow pump, a total of three fish were placed at different radial positions at a certain section of the intake passage of the axial flow pump at the initial time, and the motion trajectories of the fish passing through the runner area of the axial flow pump and the water guide mechanism were calculated. The difference between the fish-friendly pump and the prototype pump affecting the passage trajectory of the fish body before and after the optimization design was analyzed. The fish model and its passage process are shown in Figure 13.  
The speed and posture of the three fish in the fish-friendly pump were different. The three fish changed direction once at the three moments caught. The change in direction of the small yellow croaker was mainly due to its proximity to the curved surface of the hub, while the small red fish and the small blue fish had a very obvious movement to the hub side in the radial position. All three fish no longer maintained the circular motion of equal angular velocity, which made the outermost red fish, which should have had a higher linear velocity, lag significantly behind the other two fish near the inside after entering the runner.  
Figure 13: Schematic diagram of the fish model and different positions of fish passing through the axial flow pump.  
After the fish body entered the water guide mechanism, what was different from the compact and consistent motion posture in the runner was that with the increase in motion space, the increase in motion speed, and the possible influence of dynamic and static interference, the motion trend of the three fish was basically inconsistent. The three fish always moved near the hub side, still keeping the blue fish in the lead, the red fish lagging. The movement distance of the three fish ensured that their different walls collided head-on.