Study Of Internal Flow And Cavitation Characteristics Of High Head And High Power LNG Pumps

As the core power transmission equipment of LNG industry chain,LNG pump plays a crucial role in LNG production,storage and transportation,and its performance is directly related to the safety and economy of LNG industry.Since the LNG pump conveying medium is low temperature fluid,and the internal flow is characterized by high shear and strong rotation,it is easy to lead to cavitation phenomenon,which puts higher requirements on the anti-cavitation performance of LNG pump.Therefore,in order to solve the above problems,it is necessary to master the transport characteristics of low-temperature medium and cavitation characteristics considering thermodynamic effects,to reveal the internal flow characterstics and cavitation characteristics of LNG pumps,and to provide theoretical support for improving the cavitation performance and operational reliability of LNG pumps.In this paper,the internal flow and low-temperature cavitation characteristics of high-head high-power LNG pumps are studied as follows:1.The applicability of the cavitation model considering thermodynamic effects is verified in this subject.A modified Zwart cavitation model considering thermodynamic effects and a compressible modification of the flow medium are used,and the modified cavitation model is validated,and the results are in good agreement with the Hord experimental data,which verifies the validity of the model.2.The study of the flow characteristics of the full flow field of LNG pump under different flow conditions was carried out.The modeling and meshing of the fluid domain of LNG pump,experimental and numerical simulations of different flow conditions are carried out,and the prediction results are in good agreement with the experimental data,which verifies the accuracy of the numerical method;the pressure field,velocity field and flow distribution characteristics inside the pump are analyzed in depth,which reveals the internal flow characteristics of LNG pump;the entropy yield theory is introduced to characterize the flow loss of LNG pump,and the results show that the total entropy yield value inside the pump at 1.0Q working condition is the smallest,which indicates the optimal flow state.The results show that the total value of entropy production is the smallest in the pump at 1.0Q operating condition,which indicates the optimal flow state.3.The study of low-temperature cavitation flow characteristics of LNG pumps under different flow conditions was carried out.The volume distri-bution and pressure distribution of the cavitation bubbles in the impeller and the induced wheel were analyzed,and it was found that with the decreasing cavitation coefficient,the critical cavitation point lags under the low flow conditions,and the cavitation phenomenon in the induced wheel is more serious compared with the impeller;through the entropy production distribution,the internal flow loss process of the pump during the cavitation process was obtained,and the entropy production in the pump is mainly caused by the turbulent dissipation entropy production and the wall entropy production,and the wall entropy production occupies the energy loss Through the study of the effect of cavitation on the pressure pulsation of LNG pumps,it is shown that cavitation mainly has a greater effect on the pressure pulsation of the induced wheel,and the low-frequency signal gradually increases with the deepening of cavitation,and the pressure pulsation in the impeller is mainly affected by the low-frequency cavitation phenomenon and static and dynamic interference.4.The study of low-temperature cavitation characteristics under different temperature conditions was carried out for the induced wheel of LNG pump.By analyzing the internal flow characteristics and cavitation evolution of the induced wheel,it is found that the temperature has little influence on the location of cavitation,and the instability of cavitation tail increases with the increase of temperature;the existence of thermodynamic effect inhibits the development of cavitation,and the size of cavitation form is negatively correlated with temperature,and the increase of temperature shortens the length and increases the thickness of cavitation;the analysis of trend of change of gas-liquid two-phase density in the cavity shows that the thermal effect dominates The analysis of the trend of the change of the gasliquid two-phase density in the cavity shows that the thermal effect dominates the compressibility of the cavity and determines the change of the gas-liquid two-phase density in the cavity.