Turbine jet engines have become an indispensable part of aircraft in modern aviation. Further developments are always aimed at improving flight safety, turbine efficiency, overall operating behaviour and reducing noise emissions.
One of the most important components of the turbine jet engine is the single turbine blade. The characteristics of a turbine blade under different load levels and at different temperatures influences the overall engine behaviour.
One way to better estimate the fatigue life of a blade is the “low cycle fatigue” (LCF) measurement method, in which the turbine is examined before and after repeated cyclic loads. The fatigue due to thermal load is examined in more detail using “Thermomechanical Fatigue” (TMF) methods at temperatures of up to 1000°C. Model calculations of the blade geometry serve to optimize damping properties and flow behaviour, as well as to suppress unwanted resonances.
Optomet laser Doppler vibrometers offer a reliable way of precisely measuring the operating vibrations of the blades before, after and during loading and heating phases using a non-contact method. Knowledge of the vibration properties allows the determination of modal parameters and the validation of model predictions. The change in properties under different loading methods allows users to predict the expected lifetime of the turbine under real operating conditions. The results are therefore important for determining the maintenance cycles of turbines and estimating the possible lifetime of turbines under overload, for example if the remaining turbine has to be operated well above normal load to compensate for the failure of another aircraft engine.
Scanning laser vibrometer systems provide particular added value for this method, since they enable quick and easy characterization of the operating vibration shapes on the blade surface.
Due to high signal strength and signal quality of Optomet laser Doppler vibrometers, special treatment or preparation of measurement surfaces is no longer necessary. Vibration parameters can be measured precisely even on glowing and poorly reflecting objects.