Abstract
In many applications, pumps are tested against standard specifications to define the maximum allowable vibration amplitude limits of a pump. It is essential to identify the causes of vibration and methods to attenuate the same to ensure the safe and satisfactory operation of a pump. Causes of vibration can be classified mainly into mechanical and hydraulic nature. Respective unbalance masses are the two major factors which cause dynamic effects and excitation forces leading to undesirable vibrations. In this paper, the procedure of vibration magnitude measurement of a vertical turbine pump at site and the process of dynamic balancing to measure mechanical unbalance of an impeller are explained. After that, the impact of hydraulic eccentricity on the vibration displacement of a vertical turbine pump has been explained using numerical simulation procedure based on “One-way Fluid Structure Interaction (FSI).” The experimental results from a pump at site are used to compare the numerical results. After the solver validation, the one-way FSI approach is used to find the critical hydraulic eccentricity magnitude of a vertical turbine pump impeller to limit the vibration magnitudes on motor component to less than 100 μm. From the numerical simulations, it is deduced that the critical hydraulic eccentricity should be limited to 400 μm in X and Y direction. The process can be used as a guideline procedure for limiting the hydraulic unbalance in vertical turbine pumps by limiting the hydraulic eccentricity.
Highlights
Geometrical deviation in any impeller is due to the manufacturing process
One-way Fluid Structure Interaction (FSI) coupling method is used to determine the interaction between the fluid and structure to determine the vibration displacements of a vertical turbine pump
The deviation in the mapping is approximately less than 5%
Summary
Geometrical deviation in any impeller is due to the manufacturing process. A pump impeller with geometrical deviation due to the manufacturing process causes two types of unbalance: (1) mechanical unbalance and (2) hydraulic unbalance. The prevalent reasons for excessive pump vibrations are due to rotor dynamics, fluid dynamics, and structural type. The rotor dynamics causes can be studied using spectrum analysis and Bode plots. The fluid dynamic vibrations can be studied using spectrum analysis under different operating conditions. Dynamic balancing of a rotating system can be used to limit the mechanical unbalance, which is a direct method. The reason for vibration in a pump unit ranges over a broad range of causes, which includes the pump type (radial, mixed flow, or axial), operating points at the site, system resistance, type of fluid, design of impeller, and flow intake conditions.
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