Numerical investigation of crack initiation in high-pressure gas turbine blade subjected to thermal-fluid-mechanical low-cycle fatigue

Abstract

A thermo-fluid-structural analysis procedure was proposed in this study to investigate the lifespan of a realistic cooling gas turbine blade. The temperature and pressure data extracted from computational fluid dynamics simulations were applied as the loading force to calculate the strain and stress using the finite element (FE) method. Subsequently, a fatigue analysis was conducted to estimate the blade life and predict the position of cracks. Here, the fatigue model used to calculate the blade life and damage was based on the strain-life model. The results showed that although the cooling film covered the entire blade surface, inefficient cooling was still observed in some regions, such as the tip and platform, which lead to blade overheating. A high pressure distribution of approximately 1.374 MPa was formed primarily on the leading tip (LT) of the pressure side (PS) blade; this pressure decreased toward the suction side. The FE simulations revealed that temperature caused a high stress at the tip and platform regions, whereas pressure caused stress at the leading edge fillet and trailing edge (TE) root slot. Thermal stress accounted for a greater amount of stress on the blade in comparison to the pressure force. Moreover, the combination of thermal and pressure stresses increased the stress at the TE root slot. Although the maximum stress in almost all the regions was lower than the ultimate strength, cracks still appeared under low-cycle start–stop loading. According to the fatigue life predictions, cracks would appear on the TE root slot, middle-tip, trailing tip, LT, and on the PS edge platform after approximately 150, 484, 701, 673, and 374 start–stop cycles, respectively. These fatigue life estimations showed good agreement with the blade crack patterns.