Radial forces of waterjet propulsion mixed-flow pump

Fluctuations of fluid pressure in hydraulic machinery can cause resonance and fatigue da-mage of blades. In order to study fluid-induced forces, which are caused by impeller-diffuser interaction, unsteady radial forces due such an effect was conducted in a mixed-flow pump with a vaned diffuser by using CFD computation and model experiment. A closed-loop test rig was built for the pump and a co-rotating dynamometer was installed between the impeller and the pump shaft to measure the instantaneous forces and moments on the impeller. The dynamic behavior of the experimental rotor-shaft system was determined by carrying out extensive calibrations. The measured forces at the blade passing frequency showed an unexpected dependency on flow rate. Another important observation was that the blade excitation forces cause the impeller to whirl in the direction opposite to shaft rotation. The computed global characteristics and the magnitude of blade interaction forces showed good agreement with measurements, respectively. The measured results were compared with the unsteady ones estimated by using CFD code-Fluent. Over a large range of flow rates, the trend of force variation agrees well with the measurements. The reasons for deviation of prediction from experiment were explained.