# Optimal Design and Fish-Passing Performance Analysis of a Fish-Friendly Axial Flow Pump
## 6 Conclusions  
In this paper, taking the ordinary axial flow pump as the research object, a fish-friendly axial flow pump was designed, which greatly reduced the mortality of fish passing through the axial flow pump and ensured the high hydraulic performance of the pump.  
The main contents and related achievements of the full text are summarized as follows:  
1. By using the experimental device simulating the internal pressure of hydraulic machinery, the survival conditions of different fish species under different pressure thresholds were obtained, and the damage situation and damage mechanism of fish were studied. The survival threshold of _wild crucian carp_ and _yellow catfish_ was \(-40\) kPa. Other fish species should not be subjected to negative pressure. Therefore, this paper established \(-40\) kPa as the low-pressure damage threshold. At the same time, the experimental data can enrich a database for evaluating fish pressure damage, which is of guiding significance for the optimal design of axial flow pumps.
2. The runner design method of the axial flow pump was applied, and a fish-friendly axial flow pump was designed according to the blade impact model. The structure of the runner of the axial flow pump was designed under the guidance of the variables in the blade impact model, and a fish-friendly runner with a high hydraulic performance  
Figure 16: Variation curve of average pressure and shear strain rate on the whole flow channel of the fish-body axial flow pump.  
and low impact mortality was obtained based on the damage of hydraulic performance, pressure, and shear rate. This new type of runner can provide the optimization idea of geometric parameters for a subsequent optimization design of hydraulic machinery.
3. Based on the efficient boundary calculation ability of the LES-IB-LBM method for moving objects, the upstream trajectories of three fish in the axial flow pump were simulated. This method could efficiently and accurately simulate the process of fish passing through the axial flow pump. The ratio of total impact mortality of the axial flow pump before and after optimization was close to 7:1. The average negative pressure on the fish surface through the profish axial flow pump was higher than that of the prototype axial flow pump. In the process of pumping station unit design, more attention should be paid to the influence of the blade shape on fish trajectory so as to reduce the death rate caused by impacts. The LES-IB-LBM method can also be extended in follow-up numerical simulation work.  
Conceptualization, C.Y.; methodology, C.Y. and Q.Z.; software, Q.Z.; validation, J.G. and Z.R.; formal analysis, Q.Z.; investigation, J.W.; resources, Y.Z.; data curation, Z.R.; writing--original draft preparation, Q.Z.; writing--review and editing, J.W.; visualization, J.G.; supervision, Y.Z.; project administration, C.Y.; funding acquisition, C.Y. All authors have read and agreed to the published version of the manuscript.  
Key Technologies Research and Development Program (2019 YEF0105200); Central University Basic Research Fund of China (B210202060); the Fundamental Research Funds for the Central Universities (B220202005).  
Data Availability StatementData sharing not applicable. No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflict of interest.