Study On Nozzle Guide Vane Subjected To High-Temperature Shock By Thermal/Flow/Structure Coupling Method

The nozzle guide vane is installed at the exit of the combustion chamber of the aircraft engine and the high-temperature shock of the hot gas acts straightly on it,which brings high temperature gradient and thermal stress,and leads to cracks and damages on the surface.Structural strength and thermal fatigue life of nozzle guide vane subjected to thermal shock are one of the factors issues for improving thrust and reliability of the aircraft engine.The influence of high-temperature shock on the structure of nozzle guide vane is reflected in three aspects.First,the high-temperature shock will cause the temperature of the cascade fluid to be non-uniform.Second,the thermal stress at the edge of film hole is easily to be increased by high-temperature shock.Finally,thermal cyclic is a major factor in thermal fatigue of thermal barrier coat.Based on the study of classical multi-field coupling theory,a mixed thermal/flow/structure coupling simulation method for the research of nozzle guide vane subjected to high-temperature shock is established,and a test system for film cooling plate is designed to verify the accuracy of the mixed thermal flow structure coupling simulation method.Based on the simulation method,three main topics are performed here to discuss the high temperature shock resistance of nozzle guide vane with and without film cooling holes,the influence of non-uniform temperature environment on nozzle guide vane,and the thermal fatigue life of thermal barrier coat under high-temperature cyclic.The specific research work and achievements in this paper are as follows:(1)The effects of Reynolds Averaged Navier-Stokes turbulence models,mesh types,and strong/weak thermal flow coupling methodology on simulation accuracy are studied by heat transfer experimental data of Mark II nozzle guide vane which has internal radial convective cooling channels.By comparing thermal flow coupling simulation with different turbulence models,the SST-γ-θ shows good agreement with the measured data,and the maximum error is less than 10%.The predicted temperature distribution of the nozzle guide vane with unstructured grid is almost the same as that with the structured grid.The simulation accuracy of transient temperature calculated by strong thermal flow coupling simulation is better than that of weak simulation methodology.(2)To find out the error distribution law between strong and weak thermoelastic coupling element of finite element method,the heat conduction equation of a one-dimensional infinite plate affected by strong heat transfer environment is deduced and solved in this dissertation.The results show that both the strong coupling element and the weak coupling element are good at the prediction of surface temperature curve,but the thermal stress calculation result of the strong coupling element has a low precision,the relative error is near to 200%.Summarizing the simulation analysis of the previous two chapters,the mixed thermal/flow/structure coupling simulation method is established,by combining the strong thermal flow coupling and the weak thermoelastic coupling.(3)To measure the thermal strain at the edge of the film cooling holes and the non-adiabatic cooling effectiveness at the downstream of the film cooling holes,a high-temperature shock test system is constructed.Based on the digital image correlation measurement technology,a thermal strain measurement methodology for the microstructure at the edge of film cooling holes is designed,and the distribution characteristics of strain and stress around the film cooling holes are studied by both experiments and simulations.It shows that the digital image correlation measurement can effectively capture the thermal strain concentration at the edge of film cooling holes,and the maximum equivalent strain is less than 0.01.The mixed thermal/flow/structure coupling simulation method can effectively predict the temperature change of the film cooling plate,and the average error is less than 5%.The thermal strain simulate results are almost the same as the results of digital image correlation test.The holes are mainly subjected to compressive stress loads.Some locations subjected to tensile stress loads are also observed at the acute angle side of the sections of film cooling holes.The thermal stress of film cooling holes is proportional to the mass flow of cooling air.(4)Even if the nozzle guide vane reaches thermal equilibrium,the thermal stress loads of the film cooling guide vane remain in a high level.As the maximum thermal stress around film holes of the nozzle guide vane are tensile stresses,the ultimate tensile life of K409 material at different temperatures is used to evaluate the effectiveness of cooling structure.It shows that with the increase of cooling air mass flow,the service life of the nozzle guide vane decreases gradually,and the maximum life reduction is 550 h.To study the influence of non-uniform temperature environment,a high-integrity simulation method is used in the next simulation work with reference to the first-stage guide vanes of a certain type of aircraft engine.From this study,we find that the predicted temperature well caters for the temperature-sensitive paint test,between which the maximum error is less than 6%,and the location of stress concentration keeps the consistency with that of the cracks.Under the same mean inlet temperature,the maximum thermal stress increases by 19.3% with the increasing of maximum inlet temperature from 1310 K to 1800 K.(5)To reveal the thermal fatigue life of nozzle guide vane with thermal barrier coat under high-temperature cyclic,an advanced model called master-slave model is established by using mixed thermal/flow/structure coupling simulation method,phenomenological life model,multilinear kinematic hardening model,and volume element intersection mapping algorithm.The main parameters of the phenomenological life model are determined by thermal fatigue life test and finite element simulation of metal ceramic tubes under 6 typical test conditions.It is demonstrated that the maximum thermal life of thermal barrier coat is 1558 cycles around the trailing edge,which is consistent with the spallation life cycle of the ceramic top coat at1323 K,which indicate that the master-slave model has a high forecasting accuracy.With the increase of pre-oxidation time,the life of thermal barrier coat declines from 1892 cycles to895 cycles for the leading edge,and 1558 cycles to 536 cycles for the trailing edge.The predicted life of the key points at the leading edge is longer by 17.7%–40.1% than that of the trailing edge.Above all,the mixed thermal fluid structure coupling simulation method can effectively support the study of aerodynamic heat transfer,structural strength and thermal fatigue life of the nozzle guide vane subjected to high-temperature shock.The efforts of this study are promising to provide guidance for the anti-high-temperature shock study of nozzle guide vane.