Analysis On Stability Of High Pressure Self-Balancing Pump As Turbine Under Different Working Conditions

At present,China has become the largest total energy consumption country in the world.The actual utilization rate of one-time energy is less than 40%,and the oil reserves are less than 2% of the world.Therefore,it is necessary to develop new wind energy,solar energy,geothermal energy,ocean energy and biomass energy that are conducive to the sustainable development of society and ecological environment.In the energy sector,gradually reducing the proportion of consumption of one-time energy,reducing carbon emissions and achieving low-carbon development is a major measure for China's energy consumption restructuring.Pump as turbine is the earliest research and development of residual pressure energy recovery technology.It is a structural form of driving other energy-consuming machines by using centrifugal pump reversal as a turbine to apply high pressure liquid to the turbine wheel to generate shaft output power.The structure is simple,the production cost is low,and the maintenance is convenient.However,since the complex and variability of working conditions has a great influence on its safe and stable operation,it is necessary to carry out stability research on the basis of internal flow analysis.In this paper,the double-suction self-balancing multi-stage centrifugal pump is used as the research object to study the influence of different working conditions on its stability,which provides a reference for the research and application of the subsequent hydraulic turbine.The main contents of this paper are shown as following:(1)For the requirements of pump as turbine performance characteristics under the process flow of the residual energy recovery system,based on the systematic investigation and analysis of the existing pump as turbine at home and abroad,by referring to the existing structure of multistage pump,and considering the high-efficiency and high-reliability operation of the pump as turbine under high pressure,a high pressure self-balancing pump as turbine design is innovatively proposed,and the hydraulic and structural design of the prototype is completed.Based on the three-dimensional software Creo and the flow analysis software CFX respectively,the numerical calculation of the pump working condition and the turbine working condition was carried out.The test bench was set up and the external characteristic test of high pressure self-balancing pump was carried out in pump working condition,which verified the rationality of the numerical simulation method.The research results were analyzed and the internal flow characteristics of the high pressure self-balancing pump as turbine under different working conditions were obtained.(2)Through the unsteady calculation of the high pressure self-balancing pump under different flow rates and inlet gas volume fraction,the hydrodynamic characteristics of the volute,the first stage double suction impeller,the radial vane and the secondary single suction impeller of the high pressure self-balancing pump are systematically analyzed.The pressure fluctuation and radial force variation of high pressure self-balancing pump under different working conditions are obtained,revealing the internal factors affecting the stability of turbine working conditions.(3)The applicability of homogeneous flow and inhomogeneous flow in high pressure self-balancing pump as turbine is analyzed.The numerical model of high pressure self-balancing pump under gas-liquid two-phase condition is adopted by inhomogeneous flow model.The internal flow of the high pressure self-balancing pump at the inlet gas volume fraction of 5%,10%,15% and 20% was analyzed.The gas volume distribution,pressure distribution and velocity distribution in the flow channel were studied.The influence of different inlet gas volume fraction on the fluid domain of the rotor system is analyzed.The influence of the inlet gas volume fraction on the pressure fluctuation and radial force of the turbine working condition is analyzed,and the pressure fluctuation and radial force variation under the gas-liquid two-phase condition are obtained.The law provides an analytical basis for studying the stability of the rotor system under gas-liquid two-phase conditions.(4)Based on the internal flow analysis of the high pressure self-balancing pump as turbine,a fluid-solid coupling calculation model is established for the rotor system,and the ANSYS Workbench software is used under different flow and gas volume fraction conditions,the unidirectional fluid-solid coupling calculation is carried out,and the stress and displacement deformation laws of the high pressure self-balancing pump under different flow rates and different gas volume fraction are compared and analyzed.The modal shape of the rotor system with or without pre-stress is obtained.The dynamic characteristics of the high pressure self-balancing pump as turbine provide a reference for studying the stability of the high pressure self-balancing pump rotor system.(5)Using ANSYS Workbench software to calculate the transient dynamics of the high pressure self-balancing pump rotor system,the influence of flow rate and gas volume fraction on vibration displacement and vibration speed is obtained,and the vibration severity of the rotor system is obtained through calculation.The influence of the change of flow rate and gas volume fraction on the stability of the high pressure self-balancing pump rotor system.