Research On Fluidelastic Instability Characrteristics Of Heat Transfer Tube Bundles In Steam Genarator

Steam generator is an important heat exchange plants in the field of in conventional power plants,petroleum,vessels and nuclear industries.Vibration of heat transfer tube bundle induced by transverse flow inside exists widely in steam generator.Many heat exchanger failures are believed to be caused by fluidelastic instability.Fatigue and wear of tube bundles caused by fluid-induced vibration have important impacts on structural integrity and safety.As heat transfer tube bundles are always in two phase flow enviroment,where the complexity of fluid-induced vibration lead to the fact it is difficult to accurately predict the critical instability threshold.Hence,the thesis researches on the dynamic modeling and analysis methods of fluidelastic instability,fluid-induced vibration characteristics are also discussed,which not only makes contributions in control of fluidelastic instability for the steam generator,but also provides a design guideline for the safety of steam generator,which is of great practical significance in the enineering.In the thesis,the rotating triangular tube bundle is chosen,which is the most common arrangements in the steam generator.Based on Lever and Weaver's fluid channel model and Hassan's time domain model,fluid pressure and the tube bundle-flow coupling motion equation with time delay term were deduced.By numerical calculation,the time domain process of tube vibration is solved,and the vibration response characteristics of tube bundles are obtained.In order to determine the critical instability threshold,an energy analysis method is applied to the instability prediction of heat transfer tube bundles,then the critical instability velocity is solved by calculating the logarithmic growth ratio of energy in the transverse direction of heat transfer bundles.In order to study influences of flexible tubes number on the prediction of critical instability threshold in rotating triangular tube bundles,the tube bundles with a single flexible tube,seven flexible tubes and fourteen flexible tubes surrounded by rigid tubes were studied,respectively.Fluid pressure models are developed for above three tube bundles,respectively,then numerical simulations are utilized to calculate tube vibration response in time history and tube vibration characteristics are analyzed.The corresponding critical instability flow velocities are solved,and influences of flexible tube number on the prediction of the critical instability threshold in tube bundles are discussed.The flow field inside the steam generator is mainly steam-water two phase flow.The homogeneous phase flow model is adopted to calculate the void fraction and describes the composition of two phase flow.Then the fluid pressure and motion equation of tube bundles under water flow and two phase flow with different void fraction are modeled.Then fluidelastic models for tube bundles with different flexible tube number are developed respectively,the corresponding critical instability velocities are solved and the vibration response characteristics of tubes are analyzed.The influences of flexible tube number on the prediction of the critical instability threshold are also discussed for water flow and two phase flow.An experiment for rotating triangular tube bundles in the water flow and air-water two phase flow with different void fraction is conducted.The simulation results of the proposed theoretical model are compared to the experimental results,and the model in the thesis is verified.