*3.2. Fluid Field Simulation*

### 3.2.1. Computational Domain

In general, the multistage pump is composed of the first stage, the last stage, and several middle stages. To save the computational resources, the number of the middle stages was reduced to one stage and the first and last stages were still kept, as presented in Figure 3. Such simplification is appropriate to reflect the physical problems of the study object because the flow in the middle stages is similar except the initial pressure. Each computational stage includes one impeller, one vane diffuser, and the gap between the impeller and vane diffuser. Apart from the three stages, the computational stage is composed of the inlet section, the wear-ring section, pump cavity, impeller, vane diffuser, and the outlet section, which are consistent with the flow path of the experimental model pump. Both the inlet and outlet suction are extended appropriately to ensure the numerical stability, simultaneously to comply with the experimental boundary conditions.

**Figure 3.** Domains of the flow field calculation.
