Velocity measurements in a pump volute with a non-rotating impeller

Abstract

A Plexiglas laboratory pump with rectangular cross sections was tested and volute velocities were measured with a laser velocimeter. First, the pump with a four bladed rotating impeller was run at three flowrates. Second, the rotating impeller was replaced with a 32-bladed non-rotating impeller with forward facing blades that imparted a swirl to the flow under forced circulation that simulated the rotating impeller case. Velocity measurements in the discharge region and flow visualization in the entire volute indicate that the proper general flow characteristics were achieved with the flow swirler but the unsteady ‘jet-wake’ regions were eliminated. Thus similitude was attained between the rotating and non-rotating impellers allowing study of volute flow characteristics without rotating impeller effects. Two non-rotating impellers were used to provide data for comparison to future steady state theoretical analyses. One produced a flow field that represented 121% of the nominal capacity and the other represented 160% of the nominal capacity. Detailed velocity traverses were made in the volute region for both swirlers. Circumferential non-uniformities (up to 275% from the mean) were found and were largest for the 160% simulated capacity. These are not due to rotating impeller effects and are attributed to the mismatch between the exit angle of the swirler and the volute. Radial non-uniformities in velocity were also seen (up to 22%) and the largest variations were observed for 121% simulated capacity. Finally, axial variations up to 30% were observed and these also were largest for 121% simulated capacity.