Research On Unsteady Characteristics And Flow Induced Vibration Of Large Flow Rate Pumps

Pumps which act as important energy conversion and fluid transportation devices are widely used in many industries.The large flow rate pumps have larger power consumption and wider impeller channel,so that the flow inside the large flow rate pumps has a more significant three dimensional characteristics.It is easier to cause complicate flow induced vibrations in this kind of pumps,in order to make them more economic and environment friendly,the efficiency should be improved and flow induced vibration should be reduced at the same time.Steady and unsteady computational fluid dynamics calculations were performed in this thesis to simulate the internal flow of large flow rate pumps,General Euler Head Distribution,S1 Stream Surface Euler Head Distribution and Spanwise Euler Head Distribution were proposed to evaluate the pattern of energy growth inside the impellers of large flow rate pumps,the Entropy Generation Rate was introduced to locate and measure the loss generation inside pumps.The analysis methods mentioned above were applied to investigate the effects of different geometry parameters on the performance and unsteady radial forces of large flow rate pumps.Based on the deep understanding of the internal flow,the large flow rate pumps were redesigned to improve the efficiency and reduce unsteady radial forces.Finally,a redesigned large flow rate pump was tested to validate the improvements in performance and vibration characteristics,and then the flow induced vibration characteristics of this pump were studied in different operating conditions by experiments.The main contents of this of this thesis include the following aspects:1.General Euler Head Distribution was proposed to represent the pattern of overall energy growth in impellers of large flow rate pumps,it was applied to investigate the effect of the trailing-edge modification.The results are listed below:the portion of low energy growth rate is usually related to the deterioration of flow field,which indicates that the corresponding part may need modification;the best pattern of General Euler Head Distribution is a convex curve of nearly con-stant growth rate;the trailing-edge modification can reduce the jet-wake flow phenomenon near the impeller outlet and improve the uniformity of flow field,so that the performances in high flow rates are improved.2.S1 Stream Surface Euler Head Distribution was proposed to represent the pattern of energy growth on each S1 stream surface in real viscous flow,the concept of entropy generation rate was first introduced to evaluate the magnitude and distribution of the loss generation in pumps.The S1 Stream Surface Euler Head Distribution and Entropy Generation Rate were applied in the redesign of large flow rate pumps to improve efficiency and reduce flow induced unsteady forces.The results are listed below:the flow separation and secondary flow near the hub on pressure surface side of the blade is the main factor of low efficiency and excessive vibration;A "two-step-form" S1 Stream Surface Euler Head Distribution is recommended to suppress flow separation and secondary flow near the hub on pressure side of the blade in a centrifugal impeller in order to improve efficiency and reduce unsteady radial forces.3.Span wise Euler Head Distribution was proposed to represent the contribution of a certain spanwise location to the total work,it was applied to study the effects of stacking conditions on the performance and unsteady flow characteristics of large flow rate pumps.The results are listed below:the hump zone in the performance curve of the zero stacking model is related to the sud-den change of Spanwise Euler Head Distribution;the flow separation near the shroud of positive stacking model is responsible for the reduction of efficiency and increase in unsteady radial forces;the negative stacking characterised by the shroud leading the hub could improve flow stability and reduce the pressure fluctuations in pumps and decrease the unsteady radial forces of impeller.4.The final redesign model as know as the negative stacking model was manufactured and tested to validate the improvements in efficiency and reduction of flow induced vibration.The vibration characteristics of different position in pump unit were investigated under different flow rates,different inlet pressures and different cavitation conditions by experiments.The results are listed below:in low flow rate range,the increase of inlet pressure mainly influence the vibration characteristics in 10-1000Hz frequency range,in high flow rate range,the increase of inlet pressure can suppress the vibration in 1000-10000Hz frequency range;the significant time-frequency char-acteristics are observed in serious cavitation conditions.After the time-frequency characteristics are observed,the vibration of pump is first reduced and then increased as the available net positive suction head decreases.In certain circumstances,the vibrations of the pump in condition of serious cavitation are much lower than the condition without cavitation.The General Euler Head Distribution,S1 Stream Surface Euler Head Distribution and Span-wise Euler Head Distribution were proposed to evaluate the pattern of energy growth inside the im-peller of large flow rate pump,the Entropy Generation Rate was introduced to locate and measure the loss generation inside pumps.The effects of different geometry parameters on the performance and unsteady radial forces of large flow rate pumps were investigated,the improvements in the redesigned model were validated by experiments and the influences of different operating condi-tions on the vibration characteristics of the redesign pump were also studied.The results shows that the trailing-edge modification,"two-step-form" S1 Stream Surface Euler Head Distribution and negative stacking conditions can reduce the flow induced vibration and improve the efficiency,the operating conditions have significant influences on the vibration characteristics of pumps.This research can provide beneficial guidance to the design of high efficiency and low vibration pumps.