Regeneration-Induced Variances of Aeroelastic Properties of Turbine Blades

Regeneration and wear result in geometric deviations between design intent and reality of turbine blades. These deviations influence the aerodynamic flow field and the aeroelastic behaviour of downstream blades. As an example for the effect of such deviations between modules on blade vibration amplitudes, an experiment is set up to determine the influence of cold streaks, which can occur due to widening of cooling air holes. The vibration amplitude for an off-design point is increased by 20% and for the design point as well. We conclude that the forced response caused by cooling air from the turbine blades must be considered during the design process and for life predictions, especially for higher relative cooling air mass flows. Furthermore, different geometric deviations may occur simultaneously, which can magnify the vibration amplitude even further. A probabilistic process presented here investigates these combined effects. It is shown that a maximum amplitude exists within the given geometric boundaries. Using this information, new safety margins can be set for geometric deviations in the repair or manufacturing process.