| The oil industry of our country started late,and the domestic oil extraction and transmission equipment is not yet able to meet the increasing needs of oil production.As the key equipment for oil extraction,the performance and stability of the ESPs has become an important problem in the field of domestic oil extraction equipment.The existing research has not yet fully clarified the parameterization of the geometry within the hydraulic components and its relationship with the performance of ESP,while the research on its operational stability has not yet formed a complete theorical system.Therefore,in this paper,a typical ESP is studied for its blade parametric analysis and operational stability under the support of National Natural Science Foundation of China(NSFC)"Study on the influence of Reynolds number and gap scale on the unsteady flow of multistage pump in dynamic and static cavities".Based on a research method combining theoretical analysis,numerical calculation and experimental study,a parametric analysis of the impeller blade and diffuser vane of ESP was carried out.The coupling relationship between the dynamic and static cavity flow and the inter-stage leakage of ESP was investigated by taking the dynamic and static cavity structure as the entry point.The effects of the cavity parameters on the magnitude of axial force and its transient characteristics are also investigated.The main results of the research work are summarized as follows:(1)Fourth-order Bessel curve method is proposed to parametrically analyze the blade profile of impeller and diffuser within ESP.By setting fixed blade inlet and outlet angle and wrap angle,the mathematical relationship between the blade placement angle and the medium energy lifting law is determined based on the theoretical analysis;the fourth-order Bessel curve is used to parametrically analyze the blade and obtain different blade profile solutions.Based on the comparison of the single flow channel numerical prediction results of each scheme,it is found that the parametric analysis method can significantly improve the head and efficiency under high flow conditions and broaden the applicable flow range of ESP.(2)Based on the analysis of the flow in the front rotor-stator cavity within ESP,a mathematical model was established among the interstage leakage of the ESP,the speed and flow rate.It was found that the inter-stage leakage gap increase the radial pressure drop in front rotor-stator cavity of ESP,resulting in the elevation of the axial force.Through the analysis on the main stream of leakage flow,it is found that the Bodewit boundary layer will generate a flow superposition with the main stream,leading to an increase in the inter-stage leakage.On the basis of the above analysis,the method to suppress inter-stage leakage is proposed by setting a flow arrestor ring on the wall of front rotor-stator cavity,which has a good effect of suppressing inter-stage leakage under different flow conditions.(3)Through the analysis of the flow field in the rear rotor-stator cavity,it is found that the axial force generated in the rear rotor-stator cavity is significantly reduced when the dynamic and static gap is small.At the same time,the axial force has a strong transient characteristic.Through time series decomposition and Fourier transform,it is found that the main frequency signal of the axial force in the rear dynamic-static cavity is mainly determined by the impeller speed,the number of impeller blades and the diffuser vanes.Based on the above analysis,a structural scheme of using a smaller rear dynamic and static clearance with back vanes is proposed,which can effectively reduce the axial force generated by the rear rotor-stator cavity.(4)Based on the analysis of the flow field in the side rotor-stator cavity,it is found that the medium and energy exchange between the side rotor-stator cavity and the front and rear rotor-stator cavities will generate the top edge vortex structure in the side rotor-stator cavity,and also enhance the dissipation rate of the pressure pulsation.Based on the analogy between the energy characteristics of the pressure pulsation and the wave energy characteristics,the energy flow density of the pressure pulsation is innovatively defined,which could characterize the energy contained in the pressure pulsation and quantify its intensity.(5)The inter-stage dynamic and static coupling mechanism of ESP is analyzed,i.e.,the former stage diffuser vane will interfere with the latter stage impeller,and then generate the corresponding pressure pulsation signal in the flow channel.By comparing the time domain characteristics and energy flow density of pressure pulsation of each stage,it is found that the inter-stage dynamic and static interference and inter-stage propagation are the root cause of inter-stage variability of pressure pulsations.By adjusting the position of the diffuser vane outlet side and increasing the distance between the interstage dynamic and static blades,the intensity of the pressure pulsation signal generated by the interstage interference could be effectively reduced. |
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