Experimental Results for the Rotordynamic Characteristics of Leakage Flows in Centrifugal Pumps

Abstract

In recent years, increasing attention has been given to fluid-structure interaction problems in turbomachines. The present research focuses on just one such fluid-structure interaction problem, namely, the role played by fluid forces in determining the rotordynamic stability and characteristics of a centrifugal pump. The emphasis of this study is to investigate the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. An experiment was designed to measure the rotordynamic shroud forces due to simulated leakage flows for different parameters such as flow rate, shroud clearance, face-seal clearance and eccentricity. The data demonstrate substantial rotordynamic effects and a destabilizing tangential force for small positive whirl frequency ratios; this force decreased with increasing flow rate. The rotordynamic forces appear to be inversely proportional to the clearance and change significantly with the flow rate. Two sets of data taken at different eccentricities yielded quite similar nondimensional rotordynamic forces indicating that the experiments lie within the linear regime of eccentricity.

The Effect of Casing Geometry on Rotordynamic Fluid Forces on a Closed Type Centrifugal Impeller in Whirling Motion

“…The destabilizing region of Ω/ω did not change due to the clearance, though the destabilizing region is larger with a smaller clearance in the study of Ref. [5]. We can notice again the presence of the increase in normal force at Ω/ω = 0.7 for low flow rate.…”

“…However the level of the forces is more than twice that of the forces in the case of C = 5 mm, especially in Ω/ω < 0.5. Guinzburg et al [5] pointed out that the magnitude of the forces is roughly inversely proportional to the clearance. This comment is reasonable in our experiment.…”

The Effect of Inlet Swirl on the Rotordynamic Shroud Forces in a Centrifugal Pump

“…They will be summarized here. but the reader is referred to Guinzburg et al (1992) for greater detail. The effect of inlet swirl is the primary subject of this paper.…”

Rotordynamic Instabilities Caused by the Fluid Force Moments on the Backshroud of a Francis Turbine Runner

“…The rotordynamic instability of rotor systems caused by the fluid forces and moments acting on the shroud of the pump impeller were studied by many researchers. For the front shroud, the rotordynamic characteristics and the rotordynamic fluid forces caused by the leakage flows were examined experimentally [1,2], and the effect of swirl on the fluid forces was investigated in [3]. For the backshroud, the experimental results of fluid moment on a centrifugal impeller shroud in precessing motion were discussed based on the bulk flow model to elucidate the fundamental flow mechanism [4].…”

“…Reference [1][2][3] discussed the rotordynamic instability caused by the rotordynamic fluid forces under whirling motion associated with the leakage flow. On the other hand, [4,5] discussed the instability in precession motion.…”