Hydrodynamic and Structural Stability Analysis for Shaft Tubular Pump Unit

Abstract

Hydrodynamic and structural stability directly affect the efficiency and safety of pump units operation. In this paper, we simulated inner flow field of a shaft tubular pump unit through Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) for exploring the blade pressure and dynamic stress characteristics, where first part focus on the hydrodynamic pressure fluctuation on inlet and outlet of impeller and second part focus on dynamic stress distribution in time and frequency domain on pump impeller. Monitoring points are set at the inlet and outlet of impeller to obtain the dynamic pressure, then mapping the time domain data to frequency domain through Fast Fourier Transform (FFT) method. The results show that the pressure fluctuation has strong periodicity, and the fundamental frequency of the pressure fluctuation on the inlet and outlet surfaces is the blade passing frequency and the blade passing frequency respectively, which means the rotation of impeller and rotor stator interaction (RSI) phenomenon between impeller blades and guide vanes are the origin of hydrodynamic pressure fluctuation. Hydrodynamic pressure on impeller blade is applied to the impeller structure to obtain structural responses, results show that maximum dynamic stress appears in the root of impeller blade, the dynamic stress fluctuate in the nearby of static stress concentration and maximum dynamic stress appear in the permissible stress range. In frequency domain, the basic frequency and secondary basic frequency are impeller blade passing frequency and guide vane passing frequency, which indicated that the major reason of impeller dynamic stress fluctuation is water excitation pressure.