Effect of blade loading on fluid-induced exciting force and noise in centrifugal pumps
Yang Ailing1, Xu Yang1, Li Guoping2, Zhang Yi2
1.School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China; 2.704th Research Institute, China Shipbuilding Industry Corporation, Shanghai 200031, China
The unsteady three-dimensional turbulent flow fields in two centrifugal pumps are analyzed by using large eddy simulation method, then the structure vibration of the volute and the noise induced by the unsteady pressure are simulated with boundary element method. The pumps have an identical volute, impeller outlet diameter, blade outlet width, duty head and flow rate and rotational speed but different blade loadings. The hydraulic efficiency, flow field characteristics, pressure pulsation, volute vibration features and radiated noise from the pump are compared to investigate effects of the loading on hydraulic performance and fluid-induced exciting force. The results show that the hydraulic efficiency of the pump with the higher blade loading is not only 1.1%-2.9% better than that with the lower loading, but also has a more uniform flow field. The unsteady pressure on the wet surfaces of the volute and the exciting force applied on the impellers at blade passing frequency are dominated. The amplitude of pressure fluctuation in the pump with the higher blade loading is so remarkable that the maximum pressure fluctuation amplitude at the volute tongue is 42.6% higher compared with that in the pump with the lower loading. Likewise, the magnitude of unsteady radial thrust fluctuation on the pump with the higher blade loading is increased by 7.63% as well. The maximum vibration velocity and acceleration of the volute in the pump with the higher blade loading at the 2nd harmonic frequency is 5-6 times the frequency in the pump with the lower blade loading. Note that the directivity pattern of noise also shows an obvious difference in the two pumps, particularly, the sound pressure level from the pump with the higher blade loading is more violent than that with the lower loading in the range of 10°-310° polar angle. These results suggest that blade loading is an important factor that affects the exciting force and subsequently alters fluid-induced noise from a centrifugal pump. In addition, the hydraulic efficiency and exciting force should be taken into account together in design of low noise centri-fugal pumps.
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