Thermo-structural analysis of cracks on gas turbine vane segment having multiple airfoils

Thermal stress is one of major causes of cracking in high-temperature components of gas turbines. This paper presents a thermo-structural analysis of cracks on the vane of a gas turbine for power generation. The vane components include three airfoils with hub and shroud sections. The airfoils have serpentine-type internal passages and film cooling holes on the pressure-side surfaces for cooling. The conjugate heat transfer problem was solved to accurately evaluate heat transfer on the vane using computational fluid dynamics software, CFX. Based on the conjugate heat transfer result, thermal expansion and thermal stress were evaluated using structural analysis software, ANSYS. The results showed that an irregular temperature distribution induced anisotropic thermal expansion in the vane segments, including the shroud and hub sections, and that the anisotropic thermal expansion caused serious stress concentrations. Among the three airfoils, the middle one was the most stressed because the thermal expansion was constrained by deformed hub and shroud sections. The predicted locations of stress concentration coincided with the locations of cracks on the actual vane after an operating period. The prediction provides general information on the initiation of cracks on a vane segment having multiple airfoils.