PIV experiment of the unsteady flow field in mixed-flow pump under part loading condition

In order to study the rotor-stator interaction mechanism in impeller and guide vanes of mixed-flow pump under part loading condition, the flow field between the impeller outlet and the guide vane inlet under part loading condition was measured based on Particle Image Velocimetry (PIV). Besides, the relative velocity distribution along the monitoring lines in the impeller inlet and outlet sections, the relative velocity distribution and the vorticity distribution of interference field were analyzed under 0.2 times of the design flow condition at different phases. The results showed that at 0.2 times of the design flow rate, the internal flow between impeller and guide blades is affected by the rotor-stator interaction and as a result, the internal flow is disordered, conspicuous backflow and vortex flow occurred at different phases. The positive vortex structure and the reverse vortex structure both exist in the interaction zones, but the former exists near the wall while the latter exists near the hub. With the change of phase angle from impeller blade leading edge to impeller blade trailing edge, the positive vortex structure strength increases while the reverse vortex structure strength is reduced first and then increased. The relative velocity distributions at different phases in the monitor line near the guide vane inlet, due to the rectifying action of guide vane, are similar and steady. The closer the monitoring line to the impeller inlet, the more disordered the relative velocity distribution at different phase is, and the more conspicuous the rotor-stator interaction is. The maximum relative velocity difference can reach about 5 m/s on the same place at different phases. All these phenomena indicate that the rotor-stator interaction is the major source of the unsteady flow field at the part loading condition. The research results provide significant reference value for revealing the internal flow characteristics under part loading condition as well as for optimization of mixed-flow pump.