Elimination of Resonance in a Vertical Turbine Pump Using Finite Element Simulations

Vertical turbine (VT) pumps are specialized type of centrifugal pumps designed for moving liquid from deep wells or sumps. These are widely used in irrigation, power plants, water supply and various industrial applications. Current industry applications place a strong emphasis on designing pumps with vibration levels that fall within the acceptable ranges specified by applicable standards. Vertical turbine pumps inherently have long structure, its flexible nature is prone for vibration as compared with horizontal centrifugal pumps. The vibrations measured on vertical turbine pumps are caused by various factors which includes, but not limited to, hydraulic forces, mechanical unbalances, misalignments, shaft run out, pressure pulsations, loose foundation bolts etc. However, resonance creates severe vibrations when natural frequency of the structure coincides with an excitation frequency leading to failure of the pump. This study discusses resonance vibration issue experienced in a VT pump at one of the site and use of Finite Element (FE) simulations to optimize design to resolve the vibration issue.

The study is divided into three parts. Part 1 consists of detailed study of the vibration test data to understand the severity of resonance problem. Part 2 explains the numerical method using FE simulations to verify the resonance issue with experimental validation. Lastly, Part 3 describes an optimized method to resolve the resonance issue. Considering manufacturing feasibility, design optimization is required with cost effective solution to resolve vibration issue caused by resonance. It is addressed by modifying the structure to shift the natural frequency significantly away from the operating speed as per applicable standard requirements. This has also led to elimination of resonance i.e. reduction in pump vibration level at site.