# Numerical Simulation of the Tip Leakage Vortex Characteristics in a Semi-Open Centrifugal Pump  
[PERSON]  
1 Institute of Water Resources and Hydropower, Xi'an University of Technology, Xi'an 710048, China; 2  
[PERSON]  
1 Institute of Water Resources and Hydropower, Xi'an University of Technology, Xi'an 710048, China; 2  
[PERSON]  
1 Institute of Water Resources and Hydropower, Xi'an University of Technology, Xi'an 710048, China; 2  
[PERSON]  
1 Institute of Water Resources and Hydropower, Xi'an University of Technology, Xi'an 710048, China; 2  
[PERSON]  
1 Institute of Water Resources and Hydropower, Xi'an University of Technology, Xi'an 710048, China; 2
better than it with clearance. A suitable small gap could achieve higher efficiency than no gap. This finding suggested that an optimal clearance could minimize the flow loss in the impeller. [PERSON] et al. [PERSON] et al. (2019) studied a mixed-flow pump through numerical simulation and determined the following: (1) the head and efficiency were considerably affected by the shape and parameters of tip clearance, and (2) the reduction of efficiency was almost linear with the change of tip clearance under design conditions. [PERSON] et al. [PERSON] et al. (2018) and [PERSON] et al. [PERSON] et al. (2019) obtained the same findings and further determined that the slope increased with flow rate. [PERSON] et al. [PERSON] et al. (2019) investigated a low-specific speed of the semi-open centrifugal pump and discovered that external characteristics substantially decreased with the increase of tip clearance height, but the hump phenomenon in small flow conditions weakened. [PERSON] et al. [PERSON] et al. (2019) studied three different centrifugal pump gaps (1, 2, and 3 mm) and found that the tip clearance and external characteristics exhibited a regression effect, and the decline in small flow rate conditions was considerably less than that in the large flow rate conditions. The influence of the tip clearance on the external characteristics is generally complicated and related to the type of fluid machinery and operation conditions. Operational stability is an important parameter to judge mechanical performance. Numbers of studies have shown that pressure pulsation, axial force, radial force, and unsteady vortex structure are critical to operational stability ([PERSON] et al., 2010; [PERSON] et al., 2011; [PERSON] et al., 2012; [PERSON] et al., 2013). The internal flow field of the semi-open impeller becomes unstable, and the flow mechanism is complicated due to the influence of the tip leakage flow. [PERSON] et al. (2018) studied the blade wake of a centrifugal compressor with different tip clearances and discovered that the tip leakage vortex intensity increased with tip clearance size. The low-speed region near the shroud simultaneously expanded and moved to the suction surface of the blade. The tip leakage vortex mixed with the blade outlet wake and the loss in the passage and vibration increased. [PERSON] (2019) studied a mixed-flow pump under small flow rate conditions and found that the leakage in the tip region gradually increased with the tip clearance. In addition, the mixing effect between the tip leakage flow and the main flow of the impeller increased, which caused the blocking effect of the main flow in the passage. The secondary flow and the vortex, as well as other flow instability phenomena, also appeared. The tip clearance could induce the early occurrence of cavitation and increase the pressure fluctuation amplitude ([PERSON] et al., 2019). The tip leakage vortex could facilitate the possible occurrence of flow separation and vortex, especially in small flow rate conditions. The rotating stall could occur in advance [PERSON] et al. (2019). [PERSON] (2019) studied the semi-open centrifugal pump and discovered that the angle between the leakage vortex core and the camber line periodically changed with the tip blade loading.