• Korean Journal of Metals and Materials
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• v.48 no.10
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• pp.901-906
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• 2010

The first stage blade of a gas turbine was operated under a severe environment which included both $1300^{\circ}C$ hot gas and thermal stress. To obtain high efficiency, a thermal barrier coating (TBC) and an internal cooling system were used to increase the firing temperature. The TBC consists of multi-layer coatings of a ceramic outer layer (top coating) and a metallic inner layer (bond coat) between the ceramic and the substrate. The top and bond coating layer respectively act as a thermal barrier against hot gas and a buffer against the thermal stress caused by the difference in the thermal expansion coefficient between the ceramic and the substrate. Particularly, the bondcoating layer improves the resistance against oxidation and corrosion. An inter-diffusion layer is generated between the bond coat and the substrate due to the exposure at a high temperature and the diffusion phenomenon. A thickness measurement result showed that the bond coat of the suction side was thicker than that of the pressure side. The thickest inter-diffusion zone was noted at SS1 (Suction Side point 1). A chemical composition analysis of the bond coat showed aluminum depletion around the inter-diffusion layer. In this study, we evaluated the properties of the bond coat and the degradation of the coating layer used on a $1300^{\circ}C$-class gas turbine blade. Moreover, the operation temperature of the blade was estimated using the Arrhenius equation and this was compared with the result of a thermal analysis.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.738-744
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• 2011

The reliability of blade root fixing section is required to endure the centrifugal force and vibration stress for the last stage blade of steam turbine in thermal power plant. Most of the domestic steam turbine last stage blades have finger type roots. The finger type blade is very complex, so the inspection had been performed only on the exposed fixing pin cross-section area due to the difficulty of inspection. But the centrifugal force and vibration stress are also applied at the blade root finger and the crack generates, so the inspection method for finger section is necessary. For the inspection of root finger, inspection points were decided by simulating ultra-sonic path with 3D modeling, curve-shape probe and fixing jig were invented, and the characteristics analysis method of ultrasonic reflection signal and defect signal disposition method were invented. This invented method was actually executed at site and prevented the blade liberation failure by detecting the cracks at the fingers. Also, the same type blades of the other turbines were inspected periodically and the reliability of the turbine increased.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2177-2183
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• 1994

The rapid expansion or condensible gas such as moist air of steam gives rise to nonequilibrium condensation. As a result of irreversibility of condensation process in the supersonic cascade flow of low pressure steam turbine, the entropy of the flow is increased, and the efficiency of the turbine is decreased. In the present study, to investigate the flow of moist air in 2-dimensional cascade made as the configuration of the tip section of the last actual steam turbine moving blade, the static pressure at both sides of pressure and suction of blade are measured by static pressure taps and the distribution of Mach number on both surfaces of the blade are obtained by using the measured static pressure. Also, the flow field is visualized by a schlieren system. From the experimental results, the effects of the stagnation temperature and specific humidity on the flow properties in a 2-dimensional stationary cascade of a practical steam turbine blade are clearly identified.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.3
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• pp.11-18
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• 2009

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1721-1729
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• 2001

The performance of gas turbines is decreased as their operating hours increase. Fouling in the axial compressor is one of main reasons for the performance degradation of gas turbine. Airborne particles entering with air at the inlet into compressor adhere to the blade surface and result in the change of the blade shape, which is closely and sensitively related to the compressor performance. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth on the blade surface is very small compared with blade dimensions. In this study, an improved analytic method to predict the motion of particles in compressor cascades and their deposition onto blade is proposed. Simulations using proposed method and their comparison with field data demonstrate the feasibility of the model. It if found that some important parameters such as chord length, solidity and number of stages, which represent the characteristics of compressor geometry, are closely related to the fouling phenomena. And, the particle sloe and patterns of their distributions are also Important factors to predict the fouling phenomena in the axial compressor of the gas turbine.

• Journal of Power System Engineering
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• v.11 no.3
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• pp.53-58
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• 2007

The ruptured blade which is rotating at high speed can damage severely the all stage compressor blades and the turbine components. If the shattered blades flow downstream inside the turbine parts, then the turbine blades and vanes can be damaged. The small parts of shattered blades which are flowed into the turbine parts pass through without any damages in the leading edge of the first stage stationary blades. Then they bump against the convex side of the leading edge of the first stage moving blades and the trailing edge of the first stage stationary blades repeatedly. The debris of shattered blades may plug the cooling holes in the turbine blades and vanes. The dent damage and the coating delamination could be also occurred by the debris of shattered blades flowed downstream inside the combustion liner and the transition piece. This paper analyzes the influence on the turbine components and the damage mechanism and characteristics in case of the damaged blade of the multiple-stage axial flow compressor.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.8
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• pp.54-61
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• 2003

The first stage rotating blade of industrial gas turbine is one of the components that is normally run in exposed state at the highest temperature of the combustion gas stream. For this reason superior materials and advanced cooling technology are required to allow higher heat resisting characteristics of the component. The 1st stage blade of a selected commercial gas turbine blade made of directionally solidified Ni-based superalloy has a row of cooling holes on its trailing edge. In most cases, minor cracks have been found at some of the root cooling holes after one cycle operation (24,000 hrs) or even shorter operation time because of the high temperature gradient and the frequently alternating thermal stress. In the repair process, unfortunately, it is usually very difficult to get rid of the damage due to the fact that cracks are initiated at the root cooling hole and propagated deep into the hole. In this study, the feasibility of removing the sidewall cracks in the hole by utilizing EDM drilling has been investigated. Also the criteria of surface integrity for EDM drilling were established to achieve high quality repair as well as machining accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.193-203
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• 2014

Temperature-dependent stress analysis and heat transfer analysis of a rotating gas turbine blade made of functionally graded materials (FGMs) are presented considering turbine operating temperature and ceramic particle size. The material properties of functionally graded materials are assumed to vary continuously and smoothly across the thickness of the thin-walled blade. For obtaining system stiffness reflecting these characteristics, the one-dimensional heat transfer equation is applied along the thickness of the thin-walled blade for determining the temperature distribution. Using the results of the temperature analysis, the equations of motion of a rotating blade are derived with hybrid deformation variable modeling method along with the Rayleigh-Ritz assumed mode methods. The validity of the derived rotating blade model is evaluated by comparing its transient responses and temperature distribution with the results obtained using a commercial finite element code. The maximum tensile stress with operating speed and gradient index are obtained. Furthermore, the gradient index that minimizes blade temperature was investigated.

• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.61-67
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• 2016

Turbine blade cooling is one of the major technologies to enhance the performance of gas turbine and combined cycle power plants. In this study, two cases of coolant pre-cooling schemes were applied in combined cycle power plant: decrease of coolant mass flow needed to cool turbine blade and increase of turbine inlet temperature (TIT). Both schemes are benefited by the decrease of coolant temperature through coolant pre-cooling. Under the same degree of pre-cooling, increasing TIT exhibits larger plant power boost and higher plant efficiency than reducing coolant flow. As a result, the former produces the same gas turbine power with a much smaller degree of pre-cooling than the latter. Another advantage of increasing TIT is a higher plant efficiency. Even with an assumption of partial achievement of the theoretically predicted TIT, the method of increasing TIT can provide considerably larger power output.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.410-415
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• 2004

To ensure a safe operation of the prototype KGT-74 kW small gas turbine, vibrational reliabilities of the compressor 1st, 2nd, and 3rd stages and turbine blades have been estimated and reviewed. FE analyses have been carried out to obtain the natural vibration characteristics of the blades, and impact modal testings have been performed on every each one of the blades to measure their 1st natural frequencies. Then, the Campbell diagram analyses have been carried out to judge the safety of the blades from resonant failures up to 6k harmonics. Results show that the compressor 1st stage blade is exposed to a potential resonant failure with 3k harmonic around a rated speed of 30,000 rpm but that the other compressor 2nd and 3rd stages and turbine blades are safe from resonant failures. Finally, 27,900 rpm is selected as the safe operation limit for the KGT-74 ㎾ gas turbine relative to the blade vibrations.