Particle Image Velocimetry Measurements and Performance Experiments in a Compact Return Diffuser Under Different Rotating Speed.

Variable speed is the most efficient way to increase the pumping system efficiency and expand the pump application range. The detailed internal flow field in a compact return diffuser is investigated experimentally under different rotating speed. A special test rig is designed and the two-dimensional (2D) particle image velocimetry (PIV) measurements are conducted in the diffuser midplane to capture the complex flow field. The analysis of the results has been focused on the flow structure in the diffuser, especially under part-loading conditions. The pump head and design flow rate under two rotating speed is compared and analyzed. The detailed comparison between different rotating speed is performed. The strong vortical flow and recirculation flow patterns in the diffuser are captured and analyzed. Large flow separation and back flow appear under the part-loading flow conditions, and the position of the vortex core is compared. This paper provides a good data set for understanding the complex flow field in a compact return diffuser used with multi-stage pumps. [ABSTRACT FROM AUTHOR]