Rotordynamic Forces in Cavitating Inducers

Abstract

This paper reports an experimental investigation of the rotordynamic forces that occur in a whirling three bladed inducer under the influence of cavitation. The effect of lowering the flow coefficient (and thus causing reverse flows) on these forces were also investigated. The results show the occurrence of large destabilizing peaks in the force tangential to the whirl orbit for positive whirl frequency ratios. Cavitation caused these forces to become destabilizing at both negative and positive whirl frequency ratios. The magnitude of the destabilizing forces increased with decreasing vacitation numbers and flow coefficient. The rotordynamic data obtained do not exhibit the kind of quadratic functional behavior which is normally ussumed in many rotordynamic models. Consequently the conventional generalized stiffness, damping and interia matrices cannot be determined for the inducer. The results demonstrate the complexity of rotordynamic forces and their consequences on stability of axial flow inducers.

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