Laser velocimetry study of the flow field in a centrifugal pump with a shrouded impeller

Abstract

This study provides laser velocimetry measurements of the flow field within a centrifugal pump. The pump had a shrouded impeller of 254 mm diameter with five blades of backswept design. Measurements were made using a laser-two-focus (L2F) velocimetry system, both within the rotating impeller passages and in the pump volute. Both design operating conditions and off-design conditions were investigated. A comparison was made with a previous study, wherein measurements of the flow field were completed within the same pump, with an open face impeller. The absolute velocity, relative velocity, and turbulence kinetic energy levels were measured. The flow field within the impeller passages for the shrouded case was notably more uniform than for the unshrouded case. In addition, the turbulence kinetic energy within the passages was substantially lower. The efficiency of the shrouded pump was, however, lower than the unshrouded version. This was attributed primarily to losses due to leakage in the clearance region between the impeller shroud and the pump casing; a rather large passage was necessary to permit optical access. Velocimetry measurements were successfully made in the clearance region, and a leakage flow calculation was made.