Citation: Zhu, L.; Zhang, F.; Shi, X.; Adu-Poku, K.A.; Zhang, J.; Yuan, S. A Systematic Investigation on the Damage Characteristics of Fish in Axial Flow Pumps. Processes 2022, 10, 2228. https://doi.org/10.3390/ pr10112228 Academic Editors: Jin-Hyuk Kim and Lijian Shi Received: 29 September 2022 Accepted: 22 October 2022 Published: 30 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). processes Article A Systematic Investigation on the Damage Characteristics of Fish in Axial Flow Pumps Lufeng Zhu 1 , Fan Zhang 1 , Xiaotao Shi 2, *, Kofi Asamoah Adu-Poku 1 , Jinfeng Zhang 1 and Shouqi Yuan 1 1 National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, China 2 Hubei International Science and Technology Cooperation Base of Fish Passage, China Three Gorges University, Yichang 443002, China * Correspondence: fishlab@163.com Abstract: An axial flow pump is a kind of high-specific revolution vane pump that has the character- istics of large flow, low head, and high efficiency. Due to its unique properties, it is widely used in large water diversion projects, such as the South-to-North Water Diversion Project. However, during the operation of the pump, some fish enter the axial flow pump together with the water flow through the screen before the entrance of the pump station. Consequently, some fish are inevitably damaged or even die in the process of traversing through the pump. Meanwhile, the decay of dead fish directly affects the quality of water, hence, posing serious ecological pollution and destabilizing the ecological balance. Therefore, understanding the dynamics of axial flow pumps in relation to fish species in water bodies for biodiversity and ecosystem services remain vital for nature conservation. In this paper, the impact of damage of the model pump on fish is exhaustively investigated according to the theory of blade impact model, impact probability, impact mortality, and mortality distribution under different working conditions. Through the simulation of the flow state inside the impeller, the areas that are lower than the pressure threshold, higher than the shear strain rate threshold, and higher than the pressure gradient threshold in the impeller at different flow rates are analyzed. Based on the unsteady results, the volume fluctuation characteristics of the three damage mechanisms in the impeller are analyzed. Furthermore, Powell vortex acoustic equation is used to locate the high noise source region of the axial flow pump. After extensive comparison of the dipole sound source intensity, it is revealed that the dipole noise source in the impeller and guide vane is dominant. In conclusion, this study provides a holistic perspective for evaluating fish damage caused by the flow in the impeller of the axial flow pump. Furthermore, it will proffer significant references to the construction of ecological water conservancy projects. Keywords: fish; axial flow pump; internal flow; damage 1. Introduction With the growing recognition of aquatic conservation in the age of sustainable devel- opment goals, the effect of pumping activities on fish livelihood cannot be overemphasized. Because of the large flow rate, axial flow pumps are predominantly preferred in many engineering perspectives purposely for lifting water from downstream to upstream [1]. However, a large chunk of migrating fish suffer from injury and mortality when traversing through the pumping station. Several physical phenomena are revealed to be associated to the sources of fish injury as they pass through pump stations [2]. Through years of research and analysis, several scholars have basically reached a consensus that low pres- sure, high-pressure gradient, and high fluid shear force are all causative harming agents to fish [3,4]. Pan Qiang et al. [5] used a mathematical model of blade impact to predict the probabil- ity of fish and blade impact. This model comprehensively considered multiple factors, such as liquid flow velocity, blade and guide blade angle, rotational speed, and fish body length. Processes 2022, 10, 2228. https://doi.org/10.3390/pr10112228 https://www.mdpi.com/journal/processes