Numerical Investigations On Flow And Thermodynamic Characteristics Of The Turbine Cascade

Higher turbine inlet temperatures can effectively improve the efficiency of gas turbines, but the development of the heat-resisting ability of turbine blade materials is far behind the needs of improving inlet temperatures. It is urgent to explore more advanced cooling techniques. Film cooling technique is one of the main thermal protection methods of modern turbine components, researching for the flow and heat transfer characteristcs of the turbine cascade can help designers to optimize current cooling techqiques. In real turbine operation states, hign temperature、high pressure、 high rotation and high turbulence conditions make the experiments under real turbine conditions very difficult. In experimental environments, researchers usually used simplified linear cascade or numerical simulations under extreme conditions to study turbine film cooling. In this paper, three kinds of turbulence models are adopted to validate the simplifications of turbine tests, and research the flow-solid conjugate aerodynamic and thermodynamic characteristcs of a real vane cascade with complicated film cooling structures.In the simulations, commercial softwares, such as SolidWorks 2014 for modeling, Ansys ICEM 15.0 for mesh generation, Ansys Fluent 15.0 for numerical calculation, Tecplot 3602013 R1 and Excel 2012 et al. for data post-processing, are used. The main work of this thesis can be summarized as following three parts.(1)Using the Realizable k-ε、SST k-co and V2-F turbulence models, flow characteistcs in a linear plane turbine cascade with two passages in a water tunnel, are simulated under conditions of indoor temperature and pressure. The flow symmetry in span-wise direction along the mid-span section and the feasibility by using two passages to imitate real flow periodicity are validated by the three turbulence models; the secondary flow in the leading edge of vane and cascade inlet passage is studied. The numerical results indicated that the V2-F model can completely predict the secondary flow structures on all sections, and show the process of the pressure side horseshoe vortex gradually moving to the suction side in downstream flowing direction, by comparing the numerical and experimental datas.(2) Using the V2-F turbulence model, the static pressure distributions are researched on the annular cascade single channel with the periodic boundary condition at an axial rotational angle of 7.826 degrees and the plane cascade single channel with the periodic boundary condition, respectively, in two operating states of the fluid properties, the incompressible water and compressible ideal air. The differences of the pressure variation in axial downstream direction and span-wise direction between anuular and linear cascades are analyzed, and the distributions of the acceptable pressure relative errors (≤5%) are plotted. The numerical results indicate reasonable study regions, when the annular cascade is simplified to linear. Finally, the secondary flow features of the leading edge and inlet passage are displayed, in the annular and linear cascades, severally.(3) The Realizable k-ε、SST k-ω、and V2-F turbulence models are adapted and the flow-solid conjugate analysis method is introduced, to study the aerodynamic and thermodynamic charcteristics under test conditions, in the real annular cascade with the complex film cooling configuration. The numerical results obtained by different turbulence models, including static pressure distributions on the vane outside surface, total pressure loss in the passage, heat transfer coefficient and film cooling efficiency distributions on the vane, are compared. The influence of the total pressure ratio of the mainstream inlet to outlet on the performaces of fluid flow and heat transfer is discussed. The film cooling efficiency at the adiabatic wall condition is compared to conjugate heat transfer, and the effect of thermal conductivity on film cooling efficiency is pointed out.