Studies On The Thermal And Stress Performances Of Thermal Barrier Coating Under The Constrain Of Turbine Cascade Environment

High-performance thermal barrier coating coated on the turbine blade surface of an aero-engine is one of the most important ways to improve turbine inlet temperature and reduce cold air consumption;however,the complex leaf fence environment poses a significant challenge for the design of a high-reliability thermal barrier coating.To successfully withstand non-uniform heat/force loads and localized hot spots on turbine vane surfaces,the complete turbine vane is designed with variable thickness thermal barrier coating and a large number of discrete compound angle film jet holes.However,the junction between non-uniform thickness thermal barrier coating and external structural transition frequently leads to internal interface residual stress concentration,and the three-dimensional temperature gradient induced by the film cooling jet and the edge effect of film hole lead to stress concentration in the nearhole thermal barrier coating.Furthermore,the pulsation of thermal load on the wall surface caused by the mainstream oscillation of the leaf grid under cross-component interference is also a key cause of thermal barrier coating failure on the film cooling vane surface.To address the above three major issues,we present the "Mechanism of interface stress generation at the junction between non-uniform thickness thermal barrier coating","Thermal barrier coating thermal insulation performance and stress generation mechanism under multi-angle film jet confinement",and "Unsteady characteristics of coating surface temperature under the coupling of mainstream oscillation and cool air jet".This research is being carried out in order to provide the theoretical support and technical advice required for the creation of high-reliability thermal barrier coatings for turbine vanes.First,using ABAQUS finite element software,the study of the interface residual stress characteristics and optimization of the interface morphology at the junction of non-uniform coating thickness was carried out,and the propagation mechanism of the interface residual stress in the curved surface structure was revealed.Variable coating thickness can produce a 60%increase in hazardous tensile stress levels at the contact.The height difference between the two sides of the thermal barrier coating’s transition region is critical to the stress rise.Guidelines for appropriate interface morphology design are developed,and the suggested variable amplitude interface morphology decreases hazardous tensile stresses by up to 60%.The maximum increment of harmful tensile stress level at the interface caused by variable coating thickness can reach 60%.The height difference between the two sides of the transition section of the thermal barrier coating plays a decisive role in the stress increase.Guidelines for the optimal design of the interface morphology are obtained,and the proposed variable amplitude interface morphology reduces the harmful tensile stresses by up to about 60%.The growth of thermally grown oxide of interface reduces the benefit of interface topography optimization,its reduction can be controlled to less than 15%.Second,by employing the ANSYS Workbench computing platform,research is conducted on the coupled heat transfer characteristics and stress generation mechanism of various compound angle film jets and thermal barrier coatings using the three-dimensional numerical prediction technique of flow-thermal-solid coupling of thermal barrier coatings under the compound angle jet constraint,and the relationships between the coupled heat transfer characteristics and stress levels of the system and the compound angle,coating thickness and cold gas dosage are established.The results show that under the protection of the thermal barrier coating,the compound angle can only improve the comprehensive cooling efficiency of the metal in the near-hole region,while the overall average cooling efficiency is not sensitive to the compound angle.The injection of the composite angle promotes the build-up of harmful heat on the surface of the thermal insulation coating,thus increasing the risk of interfacial type Ⅱ cracking,while the location of crack generation varies clockwise along the hole edge with increasing composite angle.Increasing the thickness of the thermal insulation coating has a more pronounced effect on the coupled heat transfer properties at the 0° angle,but a more pronounced effect on the mechanical properties of the composite angle.Based on solving the high-reliability design of thermal barrier coating at the single component level,this paper is finally based on the change of thermal load on the coating surface due to strong aerodynamic pulsation in the mainstream environment of the leaf grille.By breaking through the technology of capturing the downstream temporal concentration pulsation of air film jets,the research on the nonstationary characteristics of coating surface jets under the pulsation of aerodynamic parameters in the mainstream environment is carried out to explore the non-stationary aerothermal mechanism of the coupled air film/thermal barrier coating system under the pulsation of incoming aerodynamic characteristics,and to obtain the relationship between the non-stationary characteristics of coating surface temperature and the pore length-to-diameter ratio of air film,so as to provide some theoretical guidance for the long-life design of future engine turbine blade surface coatings under the nonstationary aerothermal environment.To provide some theoretical guidance for the design of future engine turbine blade surface coatings for long life in unsteady aerothermal environment.The main results include:the mainstream oscillation induces the change of vortex structure in the near-hole region and intensifies the air film lifting,resulting in the monotonic decrease of film cooling efficiency with the increase of the mainstream oscillation frequency.Compared with the film hole with short length-to-diameter ratio,the film hole with long length-to-diameter ratio results in the highest time-averaged film cooling efficiency at all oscillation frequencies.A film hole with a length-to-diameter ratio of 1.5 is most influenced by the blowing ratio during mainstream oscillation,doubling the amount of cooling air but resulting in a reduction in film efficiency of more than 45%.The spatial and temporal evolution of the complex vortex structure in the near-wall region leads to the largest nonstationarity of the film efficiency at the near-wall surface when the length-to-diameter ratio of the film hole is 2.5.