Analysis of Losses in Centrifugal Pumps with Low Specific Speed with Smooth and Rough walls

Abstract

Numerical simulations (CFD) of industrial low specific speed pumps significantly differ from measurements. This keeps designers from using this method and rather sticking to prototyping. Experiments on a test pump with smooth walls are conducted. The influence of surface roughness on the performance is analyzed by applying micro-structured foils with realistic roughness to one side chamber. Surface roughness decreases the efficiency and needs to be considered in CFD simulations. Unsteady numerical simulations of the smooth pump are performed. A loss analysis reveals that most losses origin from volute and side chamber flow. Velocity profiles and pressure fields in these regions are in good agreement with experiments. Nevertheless, the predicted efficiency differs by 7 percent at overload. To validate rough wall models for pump simulations boundary layer measurements in a channel flow are carried out. Roughness effects on mean velocity and turbulent fluctuations are studied and applicability of wall-functions is evaluated.