| Gas turbine is widely used in the fields of aviation propulsion and power generation, and becomes more and more important for economy development and military defence construction. The increase of turbine inlet temperature is an effective method to improve gas turbine performance. Due to the limitation of turbine blade material, advanced cooling technology is needed to reduce the blade metal temperature and to guarantee the safety of gas turbine.Turbine cooling is one of the key technologies for gas turbine and has been drawn great attention. Researchers in this area have gained useful experience in open-loop air cooling through the comprehensive experimental and numerical work. Air cooling technology is well developed and nowadays the air cooled turbine inlet temperature exceeds 1700℃in aero engine and 1400℃in industrial gas turbine. However, with the further augment of turbine inlet temperature, the quantity of cooling air will also be increased, which could lead to penalty on the specific work and thermal efficiency of gas turbine, partially counteracting the gain due to the augment of turbine inlet temperature. Therefore, it is of great importance to find a cooling method that can protect the blade from high temperature gas without reduction of specific work and cycle efficiency.Closed-loop steam cooling is an advanced cooling concept and has been applied to combined cycle unit in power station. The principle of steam cooling is that "cooler" steam from the bottom cycle is used directly to cool the high temperature components by a closed-loop channel and returned to the bottom cycle finally. Compared with conventional air cooling, the closed-loop steam cooling could reduce the quantity of cooling air extracted from compressor and avoid local mixing loss, so that it could obviously improve the performance of gas turbine. Closed-loop steam cooling is one of the most advanced cooling technologies for land-based gas turbine, but few technical details are revealed in open literature. This dissertation aims at the replacement of the existing air cooling configuration in a guide vane with steam cooling. To achieve the same cooling effectiveness as the air cooling, the following main contents were studied:1. For the Mark II test case in the NASA Report, numerical simulation was performed to verify the aero-thermal coupling CFD method. The influences of turbulence model and mesh density on the numerical results were investigated.2. A preliminary closed-loop cooling structure was accomplished. the cooling effectiveness and main flow losses with the closed-loop steam cooling structure were analyzed and compared with the original air cooling structure. For the same closed-loop structure, the difference of cooling effectiveness by using air or steam as the coolant was identified.3. A certain cooling structure is used for the corresponding part of blade according to the distributions of thermal loading around the airfoil. A set of closed-loop cooling structures was designed for the parts of leading edge, middle chord and trailing edge by using a kind of zonal method. The whole cooling system was integrated with consideration of the requirement of hub and shroud cooling.4. By means of aero-thermal and thermoelastic coupling method, the compoundstress distributions of the guide vane with simple radial cooling passages were researched. The results showed that thermal stress is dominant in the compound stress, so one should pay more attention to the local thermal stress intensity due to large temperature gradients while designing a cooling structure.
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