| This study is financial supported by National Natural Science Foundation of China “The Internal Flow Mechanism of the Centrifugal Pump and Its Flow Induced Characteristics under Gas-Liquid Two-Phase Flow Conditions”(Grant No.51779170)and the Senior Foreign Expert Project “Study on Internal Flow Characteristics of Pumps in Gas-Liquid Mixed Transportation Conditions”(Grant No.GDW20153200139)In practice.,the gas in centrifugal pumps often leads a sharp deterioration in performance and threatens the safety and stability of the system.Its numerical simulation technology has always been a hot research topic.However,when gas flow in the hydraulic parts of the centrifugal pump,there are polymerization and fragmentation between the bubbles when their diameter and shape change continuously with the pressure.The numerical calculation method is not yet mature under the high gas content condition.Based on the experimental research,this paper uses three gas-liquid two-phase flow models to numerically calculate the interflow of centrifugal pump with inlet gas content increasing,which provides technical support for the centrifugal pump gas-liquid two-phase flow theory.The main research contents and conclusions are as follows:1.Through a summary analysis of the current research status at home and abroad,the experimental study believes that the change in gas-liquid two-phase flow pattern is the main reason for the decline in pump performance.The numerical calculation simplifies the the two-phase flow and ignores the deformation of the gas phase particles,which leads simulation results deviate from the actual situation.2.The calculation principles of various gas-liquid two-phase flow models are introduced as follows: 1)Ordinary two-phase model is suitable for gas-liquid two-phase flow in centrifugal pumps,but its shortcoming is that it cannot consider the effects of gas particle deformation,polymerization and splitting.2)The calculation principle of the MUSIG model is to divide the discrete phase into several groups of particles with different particle sizes and consider the polymerization and fragmentation,which is an extension of the ordinary two-fluid model.3)Modified model principle: establish an equation describing particle deformation(quoting the research content of Mark M Clark);write the equation into CEL language,introduce ordinary two-fluid model and construct a modified modelThe common point between the modified model and the MUSIG model is that the gas phase deformation is added.The difference is that the particle diameter change in the MUSIG model is caused by gas polymerization and fragmentation,while the particle diameter in the modified model changes according to the flow field parameters.3.A performance test stand for the centrifugal pump under inflow and gas conditions was built,and the external characteristics test and inlet and outlet pressure pulsation tests under different rotation speeds and different inflow and gas conditions were carried out in coMParison with the single-stage single-suction stainless steel centrifugal pump at 88.6 speed.Based on the common model,the MUSIG model,and the modified model,steady calculations and experimental verifications were carried out.The calculation results show that: 1)Under small flow conditions,the external model results are more accurate;at the rated flow rate,the error gradually increases as the inlet gas content rate increases.2)CoMPared with the ordinary two-fluid model,the MUSIG model's external characteristic results are in good agreement with the experimental data,indicating that ignoring the bubble deformation caused by gas breaking polymerization is an important reason for the calculation accuracy of the ordinary model.3)The external characteristic curve obtained by the modified model has a high degree of fitting with the experiment,and the correction effect gradually appears as the gas content increases.The correction model reduces the calculation error to a smaller range under the rated working condition,and the correction effect is most obvious.CoMParing the external characteristics of the three models,the predictions of the MUDIG model and the modified model are closer to the actual situation than the ordinary two-fluid model,indicating that the influence of gas particle deformation on the performance of the gas-liquid two-phase flow centrifugal pump cannot be ignored.4.Based on the ordinary two-phase flow model,the MUSIG model and the modified model were calculated with indefinite constant values,and the flow field velocity,flow pattern and bubble distribution obtained by the three calculation models were numerically analyzed.The results show that the flow law of uniform bubble flow state is that the gas and liquid streamlines are arranged in close order,the turbulent kinetic energy is maintained at a low level,and the bubble particle diameter is relatively large;as the inlet gas content increases,the formation of a polymerized bubble flow state: a small amount appears Reflow,the stability of the flow field is reduced;when the airbag flow occurs,the flowline backflow of the airbag portion is the most serious,the flow channel is occupied by the airbag,and the hydraulic loss increases sharply.5.Unsteady calculation and analysis of pressure pulsation,airbag evolution and pressure distribution,the law is as follows:(1)With the increase of gas content at the inlet,the amplitude of pressure pulsation increases significantly and fluctuates violently.(2)Under low-flow conditions,airbags appear at the inlet of the impeller.Under rated conditions,airbags appear near the outlet in the flow channel.(3)As the inlet gas content increases,the pressure of the volute at the outlet of the impeller drops rapidly. |
PDF Full Text Request