Abstract: Outlet divergent passages are adopted in large, low head pumping stations whose hydraulic losses are 15%～20% of pump water head. Several divergent angle clear outlet divergent passages with central partitions and without partitions are de-signed and made for vertical axial-flow pump, in which flow fields are measured and determined with five-hole probes and visualized with ligament. Formation mechanism of the flow is studied and flow regularity is analyzed, which is compared with the flow in pump outlet circle pipe. The results indicate that：under the influence of the outlet circulation of guide vane, induc-tion of pump axis, secondary flows in the outlet curved pipe and the divergence of the passage, the flow in the passage is complex spiral flow. The axial and circumferential velocities of the flow on cross sections of the passage are neither even nor symmetrical, and more uneven than that in the outlet pipe, the circulation on the section has a tendency of concentrating to outer areas of the section. Results mean much to optimum design of outlet parts of large axial-flow pump assemblies and increasement of pump assembly efficiency.

Key words: Flow fields, Outlet divergent passage, Test and measurement, Vertical axial-flow pump