EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF DEFORMATION IN THE IMPELLER OF A BOILER FEED PUMP AT DESIGN AND OFF-DESIGN CONDITIONS

Pump impellers have to be designed from two separate points of view. From a hydraulic aspect the impeller has to fulfill the specified operating conditions for flow rate, head at the speed of rotation. Additionally, from the structural point of view, the impeller must be capable to resist mechanical loads. To fulfill nowadays requirements of flexible operating conditions, the mechanical design becomes more crucial, because of increased loads at part-load operation. Consequently, trustworthy information about deformation and stress are mandatory. The present paper deals with the comparison of mechanical deformation of a pump impeller at design and off-design operation. The full loading on the impeller caused by fluid pressure and centrifugal forces is considered in experimental and numerical investigations. Therefore, an experimental model pump, representing a repeating stage of a multistage boiler feed pump has been developed. Besides performance values, transient pressure and strain measurements at the back side of the impeller rear shroud are evaluated. For the strain measurements, strain gauges are used in Wheatstone bridges to evaluate transient data. For numerical simulations a one-way coupled Fluid Structure Interaction (FSI) model has been used. Transient Computational Fluid Dynamics (CFD) simulations have been performed for the complete model pump. For the turbulence modeling Menter's SST model was used. In subsequent quasi-stationary Finite Elements (FE) simulations, the pressure loading on the impeller is taken from the CFD simulations for one impeller revolution.