Experimental investigation of the motion and shape of flexible objects near a pump inlet

Previous investigations of clogging effects in waste water pumps have focused on the impact of pumping contaminated water on the pump performance, as well as the influence of the operating point on the location of clogged material in the pump and in the pumping system. The present work aims to characterise the dynamics of flexible material entering a rotating impeller. Experiments are carried out in a wet pit located in the Department of Fluid System Dynamics in TU Berlin. The wet pit is modified with an acrylic plate placed at the bottom of the pit, enabling visual access to the suction side of the pump. Clean water containing synthetic dusters for housekeeping of size 21 cm × 30 cm are used as artificial waste water with a high degree of contamination. A high speed camera is used to capture the duster motion to identify characteristic movements of the dusters for operating points of 60%, 100% and 120% of the Best Efficiency Point (BEP). Three characteristic movements of the dusters as they enter the pump were found. Furthermore, a very clear correspondence between decrease in pump performance and the amount of visible dusters collected at the leading edge of the impeller was found for 100% and 120% of the BEP. For 60% of the BEP clogging occurred at the tongue and no correlation between visible dusters in the pump inlet and pump performance was observed.