Analysis Of Internal Flow Characteristics Of Nuclear Main Pump Under Gas-liquid Two Phase Jamming Condition Based On LBM-LES

Nuclear power is currently the second largest low-carbon energy after hydropower.Actively developing nuclear power is an important energy strategy in China and is also one of the effective energy sources to achieve the goals of "carbon peak" and "carbon neutrality".The nuclear main pump is a key equipment in the primary circuit of the nuclear island,whose main function is to drive the continuous circulation of high-temperature coolant,prevent core overheating,and is crucial for the safe operation of nuclear power plants.In order to ensure the safety of nuclear power plants as much as possible,it is necessary to be able to withstand the tests of various accident conditions.Stuck shaft accident is a typical extreme fault,which can cause accidents such as rotor system friction,shaft breakage,water hammer,and even seriously threaten the safety of nuclear power plants.This article focuses on the refined numerical simulation of the gas-liquid two-phase transient transition process of the nuclear main pump under the stuck shaft working condition,with a focus on studying the internal changes of the nuclear main pump under the gas-liquid two-phase situation during the accident process,providing theoretical basis and technical support for optimizing and improving the nuclear main pump.The main content of the specific research includes:1.A brief introduction to the traditional CFD calculation theory and several turbulence models related to the numerical simulation in this article,and an introduction to the theoretical development of the lattice Boltzmann method and typical boundary processing methods,analyzing their respective advantages and limitations in numerical simulation.In order to combine the advantages of both,LES Smagorinsky is introduced based on the LBM theory,paving the way for the selection of numerical simulation methods in the future.2.In order to accurately obtain the fine transient characteristics of the nuclear main pump during the stuck axle accident,based on the globally structured grid with an encrypted boundary layer,the flow rate and speed change rules obtained in the experiment are used as boundary conditions.Three different numerical simulation methods,namely,standard "k-ε",DES,and LES,as well as the fast Fourier transform data processing method,are used to conduct fine numerical simulation and research on different stuck axle conditions,revealing the advantages of LES simulation in dealing with such complex flows.It is found that as the stuck axle accident progresses,the vorticity and specific energy in the pump increase first,reaching the extreme value when the impeller stops rotating,and then slowly decrease.The amplitude of pressure pulsation in the impeller flow passage gradually decreases due to the effect of dynamic and static interference,but the low-frequency pulsation strengthens.3.To obtain the fine transient characteristics of the nuclear main pump and explore the influence of gas content on the performance of the nuclear main pump during the gas-liquid two-phase locked rotor condition,the standard "k-ε",LES,and LBM-LES methods were used to perform fine numerical simulations on the steady state and locked rotor conditions of the nuclear main pump under different inlet gas content rates.The effects of inlet gas content rate on pump head and efficiency were obtained,as well as the transient distribution of gas phase and vorticity during the locked rotor accident.In order to accurately analyze the pressure pulsation at the impeller outlet,the transient pressure signals at the pressure and suction surfaces of the impeller outlet under different conditions were analyzed using discrete wavelet transform.The results show that the LBM-LES method has higher simulation accuracy for the complex conditions of two-phase flow due to the advantage of the lattice method in handling the interaction between different media.When the inlet gas content rate increases,the vorticity value in the impeller flow passage increases but decreases at the outlet.The amplitude of pressure pulsation at the blade outlet increases with the increase of gas content rate,and the main impact is in the high-frequency band of the early stage of the locked rotor.4.Aiming at the special nature of gas-liquid two-phase locked rotor accidents,a gas-liquid two-phase locked rotor test bench for nuclear main pump was designed and constructed.The CAP1400 nuclear main pump model was used as the test object to explore the changes of flow rate,head,speed and other characteristic parameters of the nuclear main pump with time under different degrees of locked rotor and different gas content rates,and to compare with the numerical simulation results.The study identified the numerical simulation methods with relatively higher accuracy,indicating that both single-phase and gas-liquid two-phase locked rotor numerical simulations have reliable accuracy,with the LES method being more accurate in the single-phase simulation and the LBM-LES method being more accurate in the gas-liquid two-phase simulation.