Dynamic surface temperature measurement on the first stage turbine blades in a turbofan jet engine test rig
Turbine blade surface temperatures were studied during transient operation in a turbofan engine test rig. A single fiber radiation pyrometer was used to view the suction side of the blades from approximately 60 percent axial chord to the trailing edge at an average radial location of 70 percent blade height. A single ceramic-coated blade produced a once-per-revolution signal that allowed for the tracking of individual blades during the transients. The investigation concentrated on the light-off starting transient and the transients obtained during accelerating and decelerating between power settings. During starting and acceleration transients, the blade surface temperature gradient was observed to reverse. This phenomenon was most apparent during starting when the trailing edge was initially much hotter than the 60 percent chord location, resulting in large temperature gradients. In steady operation the trailing edge temperature was lower than the 60 percent chord location, and the gradients were less severe. During deceleration transients, the trailing edge cooled more rapidly than the 60 percent chord location. This resulted in larger temperature gradients than were seen in steady operation, but no profile inversion was observed. These temperature gradients and profile inversions represent a cycling of thermally-induced stresses which may contribute to low cycle fatigue damage. A simple one-dimensional heat transfer model is presented as a means of explaining the different heating rates observed during the transients.