# Characterisation of the Pump-Suction Flow Field of Antarctic Krill and Key Influencing Factors
## 1 Introduction  
Antarctic krill (Euphausia superba, hereafter krill) is currently the largest single species of marine biological resources known to be commercially exploitable. It has a biomass of 650-1000 million tons. In the Southern Ocean, krill are an integral part of the marine ecosystem and are dependent on sea ice during their early life stages. They are a primary prey source supporting a diverse assemblage of marine predators including whales, seals, penguins, and flying seabirds. They also play a role in nutrient cycling and are the target of the Southern Ocean's largest fishery [1, 2, 3, 4, 5]. It is considered to be a significant reservoir of protein for human consumption and has the potential to become China's second ocean fishery. Krill is a rich source of nutrients, including phospholipids, polyunsaturated fatty acids, and astaxanthin. The development of high-value-added products, including functional foods, pharmaceuticals, health products, and high-end aquaculture feeds, is a potential outcome of this research [6, 7]. The prospects for the development of a high-value emerging marine biological industry are significant. In the context of industrial krill fishing, the configuration of the pumping apparatus constitutes a pivotal scientific concern, determining the biological integrity of the target species and the economic viability. During operation, the pumping device utilises a high-speed rotating impeller to generate negative pressure, thereby drawing the krill-water mixture into the pipe. Inadequate or improperly configured pump speed, flow rate, or pressure parameters are likely to result in two primary issues during the fishing process. Firstly, excessive mechanical forces may cause the krillshells to fracture, leading to a 20% to 35% loss of individual integrity [8]. Secondly, the fragmented krill tissue may impede the filtration system, necessitating frequent stoppages for cleaning, which will increase maintenance costs. The centrifuge is the primary structural element of the krill pump. The centrifuge possesses a complex internal mechanical structure, which engenders an extremely complicated flow field inside. The interaction between impeller rotation and surface curvature gives rise to a multitude of phenomena, including separation, reflux, and secondary flow, thereby further augmenting the intricacy of the fluid flow within the impeller [9; 10; 11; 12; 13]. [PERSON] et al. [14] used a simulation to characterise the drag reduction performance of a centrifugal pump using its torque variation, considered the influence law of structural parameters such as the morphology of the bionic structure, the cross-section shape and the characteristic height, and revealed the influence mechanism of the bionic structure on the drag reduction characteristics of the centrifugal pump through the analysis of the vane surface velocity contour. [PERSON] et al. [15], in order to further study the transient working condition of high-specific-rpm high-power centrifugal pumps, applied flowmaster software to build a centrifugal pump operation model, and the boundary conditions were set up according to the actual measured parameters to simulate and compare with the test results, and the simulation analysis was carried out for the different starting modes of the pumps in a credible manner to quantify the advantages of a start-up process. The merits of initiating the process, predicated on the characteristic curves of instantaneous starting speed, flow rate, power, and outlet pressure of the centrifugal pump being obtained at varying valve openings and then analysed by quantitative normalisation. [PERSON] et al. [16], based on the detailed analysis of Large Eddy Simulation (LES), carried out an in-depth analysis on the mechanism of loss generation in in-line centrifugal pumps operated under real conditions. The results showed that there is a strong interaction between the components. [PERSON] et al.