In the gas turbine, the clearance between the blade tip of the rotor and the inside of the stationary casing varies depending on the rotation of the rotor and the heat output of the combustor. Accordingly, the assembly clearance is determined, and the leakage of the gas occurs because of the gap during operation, affecting the efficiency of the system. Thus, designers use a variety of techniques to optimize this clearance, a typical method that reduces the relative variation of the clearance using heating and cooling mechanisms. In this study, we developed a method to control the blade tip clearance through the axial movement of the inclined blade without using heating and cooling mechanisms. Recently, we designed an advanced blade tip clearance control system that can control multi-step, not on-off control, to apply to large gas turbines developed by Doosan. The designed system is hydraulic and can be used with a maximum thrust of 100 tons, and the desired displacement can be moved in multiple stages as required. We have completed the reliability verification of the entire lifecycle level and applied it to the newly developed gas turbine.

The purpose of this study was to investigate the flow characteristics and cooling performance for the heavy turbine blade with different shapes. Research was focused on the numerical study on forced convective heat transfer coefficients for three different blades with base, tip, and hole. Thus, selected local locations for various temperature distributions were shown in the flow domain. Final temperature on the local surface of blades was compared with three different blades. According to the results of velocity and temperature distributions in the fluid domain, the blade with holes had the best convective cooling performance with higher 13-16% average heat transfer coefficient than the other two blades. Apparent vortex at the tip of tip and hole blade caused the stable temperature drop. According to the calculations of local convective heat transfer coefficient between blade surface and atmosphere in the blade, approximately 18% of heat transfer coefficient at hole was higher than the base blade and 7% at hole blade was higher than the base blade. Lowest cooling performance existed at the center position of all three blades.

A gas turbine is a power plant unit that converts thermal energy into rotational energy by rotating a blade using hightemperature and high-pressure combustion gas. A gas turbine blade is directly exposed to a high-temperature flame. Various studies have aimed to improve the durability of the blade in harsh conditions. One proposes coating the blade with a thermal barrier to protect it from the flame, using a ceramic material with better thermal insulation. Another proposes using internal cooling, by creating an air flow path inside the blade to lower its temperature. Because both these techniques create a thermal gradient in the cross section of the blade, they amplify the difference in thermal expansion, thereby producing thermal stress in the blade and the thermal barrier coating. This study investigates the internal cooling effect on thermal gradient fatigue by using finite element analysis.