Gas turbine blade stress analysis and mode shape determination using thermoelastic methods

Abstract

The efficacy of thermoelastic stress analysis for use in the study of moderately curved gas turbine blades is considered over a frequency range of 68 Hz to 3.4 kHz. A selection of blades, both industrial examples and simplified planar laboratory specimens, are excited at their natural vibration frequencies using both electromagnetic shakers and piezoelectric stack actuators, in order to develop a cyclic displacement of the blade surface and hence a cyclic variation in surface stress condition. Results are shown using both snapshot array and rolling array infrared detector systems, and the data then used to generate maps of normalized principal surface stress sum, and hence the mode shapes of vibration, including the first four excitation modes.