Studies of Rotordynamic Forces Generated by Annular Flows

Citation

Uy, Robert Vincent (1998) Studies of Rotordynamic Forces Generated by Annular Flows. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9nq0-qp03. https://resolver.caltech.edu/CaltechETD:etd-03272007-111205

Abstract

Fluid-induced rotordynamic forces in pumping machinery are well documented but poorly understood. The present research focuses on the rotordynamics due to fluid flow in annuli, in particular, the discharge-to-suction leakage flow in centrifugal pumps. There are indications that the contribution of the front shroud leakage flow can be of the same order of magnitude as contributions from the nonuniform pressure acting on the impeller discharge. Previous investigations have established some of the basic traits of these flows. This work further elaborates both the experimental and computational approach to quantify and predict the shroud contribution to the rotordynamic stability of pumping machinery. Experimental results presented show the contributions of the curvature of the leakage path to the rotordynamics both with and without inlet swirl. The effect of different inlet swirl rates at constant flow rate is examined. Anti-swirl devices are evaluated for their effectiveness in reducing instability. Geometrical changes to the high-pressure and low-pressure seals for the leakage path are quantified. All results are in good agreement with other reported measurements. Childs' bulk flow model for leakage paths is carefully examined, and convective relations for vorticity and total pressure are deduced. This analysis suggests a new solution procedure of the bulk flow equations which does not resort to linearization or assumed harmonic forms of the flow variables.

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