# Influence of Cutter Head on Cavitation of Non-Jammed Submerged Grinder Pump
## 1 Introduction  
A non-jammed submersible grinder pump is equipped with a grinding device for grinding debris at the inlet of the vortex pump. It can effectively cut and grind the debris entering the inlet of the vortex pump, therefore ensuring that the vortex pump has better performance when conveying sewage. The non-jammed submersible grinding pump can grind domestic sewage containing gloves, cotton yarn, sanitary napkins and bones or other debris thoroughly. Thus, it is widely used in rural areas, hospitals, hotels, domestic wastewater and sewage discharge. The grinding device of a non-jammed submersible grinding pump is composed of a movable cutter head and a static cutter head. The sundries are ground through the cooperation of the cutter head on the movable cutter head and the semi-circular flow channel of the stationary cutter head, and finally, small particles are formed. The particles enter the impeller channel [1]. In recent years, a series of investigations on non-jammed pumps and grinding devices have been carried out. [PERSON] [2] summarized the current research status and development trends of non-jammed pumps. [PERSON] [3] proposed a practical design method for non-jammed pumps based on his design experience called the Drawing Method, designing the pump by drawing it in software after the determination of some important parameters. [PERSON] [4] studied the hydraulic performance and pressure pulsation characteristics of grinder pumps under different clogging conditions; it was found that with increase in the number of static cutter heads, the clogging degree of the flow channel increases, the head changes into a parabolic shape and the maximum efficiency point is shifted to a low flow point. The passing frequency of the dynamic cutter is the most important factorthat affects the pressure pulsation. When part of the static cutter runner is completely clogged, the interaction between the dynamic cutter and the stationary cutter is the most important factor affecting the pressure pulsation. Static cutter models with different degrees of clogging are shown in Figure 1. [PERSON] [5] conducted research on the cavitation and pressure pulsation characteristics of a non-jammed submerged grinder pump. It was found that, as the level of runner blockage increased, the cavitation close to the cutters was intensified and became more serious; the cavitation at the back of impeller inlet also became more serious. Cavitation distribution inside grinder pump at different degrees of blockage is shown in Figure 2.  
For the study of cavitation in pumps, various investigations have been carried out. [PERSON] [6] studied cavitating flow-induced unsteady pressure pulsations in a low-specific speed centrifugal pump. It was found that the cavitation cloud in a typical stage is partially compressible, and the emitted pressure wave from a collapsing cavitation bubble is absorbed and attenuated significantly. The cavitation performance and cavitating flow structures of a centrifugal pump are shown in Figure 3.  
[PERSON] [7,8] proposed a novel and fast cavitation prediction method based on the impeller pressure isosurface in single-phase media. The feasibility of this method was demonstrated in combination with experiments, which greatly accelerated pump hydraulic optimization design in engineering, and the investigation evaluated the sensitivity and accuracy at different flow rates. [PERSON] [9] conducted research on the hydrodynamics of high-velocity regions in a mixed-flow pump based on experimental and numerical calculations at different cavitation conditions. High-speed photography technology was used to capture the cavitation flow structures and reveal the physical process of cavitation evolution in a mixed-flow pump.