Research On Rotor Dynamic Characteristics Of All Metal Single Progressive Cavity Pump With Liquid-Film

All-metal single progressive cavity pump(PCP)is suitable for high gas,high sand,heavy oil and high temperature wells and can be applied to the exploitation of high viscosity heavy oil wells.In the process of increasing the speed of pump,it is easy to appear the problem of unstable operation.In order to prevent the instability of operation state from affecting the safety of the pump body or the whole oil production equipment,it is essential to study the dynamic characteristics of the rotor.The rotor system of all-metal single PCP has complex dynamic characteristics because of nonlinear liquid film force,the clearance between rotor and stator and working speed.So it is of great significance to analyze the effect of different factors on the stability of pump and find the reasonable operating parameters to maintain the smooth operation of pump.Taking the rotor system of all-metal single PCP as the research object,and the force analysis of the rotor is carried out.According to the fluid lubrication theory and combined with the structural characteristics of the rotor,the nonlinear liquid film force models of arc and straight sections are derived.Considering the force,working principle and motion characteristics of the rotor system,the model of eccentric rotor with flexible support is established and the motion differential equation of the rotor system is calculated by Lagrange equation.The differential equation is treated dimensionless,and then the fourth order Runge-Kutta method is used for numerical calculation.The trajectory diagram,phase diagram,bifurcation diagram and Poincarémap of the rotor system under the different effect factors are obtained.In order to study the effect of different parameters on the response of rotor system,the vibration characteristics of the system under the influence of rotational speed,clearance value,coupling of rotational speed and clearance and coupling of viscosity and clearance are analyzed.The results show that the transition between multi period motion and chaos occurs with the increase of rotational speed.A smaller clearance value is beneficial to reduce the maximum value of the system and there is a clearance interval of 0.1～0.4mm,so that the maximum vibration amplitude of the rotor system can be significantly reduced.When the clearance value is less than0.4mm,the maximum amplitude of the system is greatly affected by the speed and the maximum amplitude of the system gradually decreases with the increase of speed.At this time,the system is stable when the speed is around 62.6rad/s;When the clearance value is greater than 0.4mm,the value can greatly affect the maximum amplitude of the system.The increase of viscosity can effectively restrain the influence of clearance on the maximum amplitude of the system.It reflects that when the clearance value is less than 0.3mm,the medium viscosity has little effect on the maximum amplitude;When the clearance value is bigger than 0.3mm,the maximum amplitude decreases with the increase of viscosity.The results reveal the influencing factors of rotor system stability and the rule of vibration response,which have great significance to the optimize the design of rotor system,and provide theoretical basis for further research on the stability of all-metal single PCP.