Subproject C4 Aeroelasticity of Turbine Blades

The blade geometry of aircraft engines deviates from the original geometry because of wear and the maintenance process. Variations are for example the thickness distribution, blade length and stagger angle. These geometry parameters can have an influence on the vibration excitation of downstream rotor cascades and have been investigated individually so far. Such deviations occur in combination in reality. To reproduce this in a model, geometries are generated based on probabilistic calculations and aeroelastic simulations are carried out. The results then allow the derivation of blade tolerance bands. With the help of these, it can be ensured that the regeneration process causes no critical vibration states. 

High-pressure turbine blades are exposed to enormous thermal loads due to the upstream combustion chamber. Therefore, the first turbine stages must be cooled. This is realized by means of air bleed from the compressor. The cooling air is directed to the blade surface via boreholes. The high thermal and aerodynamic loads cause heavy wear on film cooling holes, trailing edges and seals. Because of wear, cold streaks can propagate downstream through the turbine and cause rotor vibrations, which can shorten the lifetime of the blades. This type of excitation is investigated at the air turbine of the TFD by injecting cold streaks into the flow and measuring the resulting vibration amplitudes with a tip-timing system.

Currently, the calculated mixing behavior of cold streaks is analyzed and appropriate points of measurement are derived for later experiments. The numerical results are validated by means of the experiments. The subprojects A3 (Exhaust Gas Analysis) and A6 (Mixing and Burner Signature) are supplied with the information. In addition, a tool chain for the investigation of combined parameter variations will be set up. The results contribute to the selection of an appropriate regeneration path in the overall project.