Performance of vortex pump in CFD simulations with rough walls

Flow passages in vortex pumps usually have rough walls. Precise consideration of wall roughness is an important issue in pump flow simulations. Numerical studies of the effects of wall roughness on the performance of vortex pumps are quite rare, especially with different interface models. Turbulent flows of water in a vortex pump with a specific speed of 76 are simulated using 1/8 and whole impeller fluid domains with rough walls, using the three-dimensional Reynolds-averaged Navier–Stokes equations, the standard k-ɛ model, and a scalable wall function in Ansys CFX 2019 R2. Equivalent sand grain roughnesses ks = 0.586 and 9.38 μm are determined for the chamber casing, volute, and suction pipe, and ks = 18.47 and 36.94 μm for the impeller by using the arithmetic average roughness Ra of the materials used in the pump and the correlation between ks and Ra given in the literature. The mixing loss along the interface between impeller and volute in the transient rotor model is determined. The rates of change of the head, shaft-power, and efficiency of the pump due to wall roughness are calculated. The transient rotor model with whole impeller domain and the frozen rotor model with 1/8 impeller domain for rough walls with Ra = 0.1 μm in the suction pipe, volute, and chamber and 3.2 μm in the impeller give the most accurate predictions of pump performance compared with experimental data. The transient rotor model with whole impeller domain gives more accurate predictions of pump performance than the frozen rotor model with 1/8 impeller domain. The mixing loss rises quickly at high flow rates. The transient rotor model with whole impeller domain gives plausible predictions of the rates of change.