Investigation Of Low-Specific-Speed Centrifugal Impeller Fluid-Induced Excitations And Its Control Methods

With the development of hydraulic machinery in the direction of high-speed and high-energy density,centrifugal pumps with the advantages of simple geometry and stable operating are commonly used in medical,aerospace,and other precision fluid circuit systems to provide dynamic energy for the fluid.To ensure the performance of the fluid circuit systems,these application scenarios have high requirements on the vibration,noise,and flow stability of the mechanical pumps.Due to the relatively small flow rate and high head operating parameters,highspeed low-specific-speed centrifugal pumps with relatively larger impeller diameters,and narrow outlet widths are often used in which the impeller flow channel is seriously diffused.The internal flow structures are extremely complex and accompanied with significant backflow,secondary flow,wake-jet structure,and etc.The fluid excitations induced by internal complex unsteady flow are the root cause of pump vibration,noise,and unstable flow.Since the flow-induced excitations mechanism and response characteristics of the low-specific-speed centrifugal pump are not very clear,the design of the low-vibration pump hydraulic model is mainly based on computational fluid dynamics(CFD)methods,combining with the accumulated experiences in low-vibration pump design.The entire design process takes a lot of time and computational resources,especially for the pump with low-sensitivity vibration.Therefore,it is very important to study the internal flow-induced excitations mechanism of low-specific-speed centrifugal pumps and develop efficient control methods for low-vibration hydraulic model design.This paper includes the following three aspects:(1)A low-specific-speed model pump is designed to investigate the mechanism of flowinduced excitations by experiments and numerical simulations.The internal pressure pulsations,exciting forces,and vibration acceleration of the model pump are monitored under various operating conditions for capturing the flow-induced excitation characteristics of model pump under both rated and partial conditions.Meanwhile,combining with the internal flow visualization,the mechanism of flow-induced excitations in the model pump are deeply explored to reveal the root cause of flow-induced excitations.(2)The characteristics of the main flow-induced excitation sources in the model pump impeller are deeply investigated and analyzed.Combining with mathematical methods,corresponding passive control methods are proposed to suppress various flow-induced excitation sources and improve pump vibration performance.Including the design method of increasing the number of blades based on single-blade loading reduction,the pressure surface modification method based on the suppression of wake-jet structure,and the blade thickness design method based on the suppression of secondary flow.Based on the proposed control methods,various impellers are designed and manufactured to investigate the effects on external and dynamic characteristics of the model pump by experiments.Meanwhile,visual and quantitative analysis of the internal flow field based on numerical simulations are carried out to reveal the optimization mechanism and clarify the dominant factors of fluid-induced excitations.Related internal flow field quantification parameters are also proposed to predict the strength of fluid-induced excitations.(3)Based on the verified flow-induced excitations control methods of the model pump,the low-specific-speed centrifugal impeller blades are parametrically modeled,and the proposed quantified parameters of flow-induced excitation sources are selected as target parameters to build an optimization model.This method is applied to the low-vibration hydraulic model design of a low-specific-speed centrifugal impeller,and the optimization effect and internal mechanism are verified by experiments and numerical simulations.In this paper,the investigation of flow-induced excitations mechanism of low-specific-speed centrifugal pump are carried out by experiments and numerical simulations and main flowinduced excitation sources are identified and quantitatively analyzed.Based on different excitation sources,the corresponding flow-induced excitation control methods are proposed and quantitative parameters of internal flow field are proposed to predict the intensity of fluid-induced excitations.Based on the research results of the model pump,an optimal design method for the low-vibration hydraulic model design of a low-specific-speed centrifugal impeller based on the suppression of flow-induced excitation sources is established.This paper aims to provide a reference for the vibration reduction design of the low-specific-speed centrifugal pumps.