Prediction of Flow-Induced Vibrations due to Impeller Hydraulic Unbalance in Vertical Turbine Pumps Using One-Way Fluid−Structure Interaction

Abstract

Vertical turbine pumps are used for critical application in power plant. Apart from power plant, these are also used in irrigation, water supply, process industries and petrochemical industries. Centrifugal and vertical turbine pumps consist of rotor geometry and a structure that can vibrate in response to excitation forces. Mass unbalances associated with mechanical and hydraulic geometry of a pump are the two major factors which create dynamic effects in terms of pump vibrations. The generated hydraulic forces resulting due to hydraulic unbalance have similar effect as of mechanical unbalance. For satisfactory operation of the pump, the vibrations in the pumps must be within acceptable limits of applicable standards. Higher level of vibrations not only leads to operational loss, but also leads to down time due to premature failure. Therefore, it is of vital importance for product designers to understand the dominating cause of unbalanced force and its source. The estimation of vibrations using numerical methods can help a designer, especially vibrations arising due to the hydro dynamic forces, for a successful design. In any centrifugal pump, including vertical turbine pump, there is always interaction between fluid and structure. Solid and fluid interaction in present case can be completed by one-way coupling method. The one-way fluid−structure interaction approach is presented in the present paper to predict the vibrations at specific operating conditions which have significant correlation with the test data. Similar philosophy has been applied for an impeller geometry which has hydraulic unbalance to predict the impact of hydraulic unbalance. The benefit of reduction in computational effort and time in this approach can be applied during the initial design stage. Two case studies of one-way FSI approach of a vertical turbine pump are discussed. The approach can be used for evaluating the impact of geometrical deviation, especially vane pitch in an impeller in terms of vibration displacements.