Rotordynamic analysis of a centrifugal pump for automotive applications

A proper design of a high speed rotating machinery cannot be performed without a deep understanding of the rotor-dynamic aspects involved. The main purpose of the present work is to show how different methodologies can be adopted and integrated, in both preliminary and detailed design phases. The study focused on the dynamic analysis of a centrifugal pump for automotive applications, called purge pump, whose role is to take the air and gasoline vapor mix from the canister to the intake manifold of combustion chambers, in order to reduce emissions. It is quite small and rotates at a constant relatively high speed. The dynamic models were developed using commercial software widely used in companies and in the academic environment. First, an analytical model was devised with all the components assumed as rigid, except the supports. Then a 1-D Finite Element model of the shaft was created with lumped masses and finally a full flexible multibody model for transient analysis, which requires much more computational time with respect to all the other approaches but provides more information, was developed,. In addition to unbalance, localized defects in the pump ball bearings as source of vibration for the pump were investigated. In particular, a detailed 3-D model of faulty ball bearing was set up using a rigid multibody commercial code in order to simulate a localized defect and to evaluate the dynamic load produced. The presented set of methodologies can be a useful tool to understand the critical aspects of the design, as well as to predict the dynamic response and to suggest suitable modifications for a better rotor-dynamic behavior of the whole system reducing vibrations and consequently acoustic noise and improving structural reliability.