| The demand for higher efficiencies and performance of modern centrifugal turbomachinery requires improved knowledge of critical design factors in strength of materials, aerodynamics, and rotordynamics. While tremendous strides in finite element stress analysis and computational fluid dynamics (CFD) have addressed the first two areas, the lack of accurate prediction tools for centrifugal impellers typically leaves rotordynamics out of the design loop. While several authors have analyzed the rotordynamic forces arising from shrouded centrifugal impellers, there has been no study to couple the secondary shroud passage with the three-dimensional primary flow model. The strong interaction between these domains makes this approach advantageous. The current study utilizes CFD techniques to analyze the full 3D viscous, primary/secondary flow field in a centrifugal pump impeller to determine rotordynamic forces. Multiple quasi-steady solutions of an eccentric, 3D model at different precessional frequency ratios yield the rotordynamic impedance forces. Performing a second order, least-squares analysis generates the skew-symmetric stiffness, damping, and mass matrices. A grid independence study is performed in all cases. The approach is first benchmarked against laser Doppler anemometer measurements for a grooved annular seal and rotordynamic force measurements for a plain annular seal and an isolated shroud passage. The analysis of a boiler feed pump impeller shows good correlation with experiment for both performance and rotordynamic forces. A parametric study shows the effect of rotation speed, operating fluid, and geometry on the predicted rotordynamic impeller forces. |
