Subproject C4 Aeroelasticity of Turbine Blades

The subproject C4 investigates the influence of regeneration-related, geometric variations of turbine blades on the aeroelastic properties of downstream blades. The focus is on the investigation of combined geometric variations. For this purpose, probabilistic approaches are used and tolerance bands are derived, which are used in the regeneration process. Another focus is on wear- and regeneration-related disturbances from upstream modules of the entire engine, which propagate as thermal streaks through the turbine. The goal is to investigate the mixing behavior and the potential to cause blade vibrations.     

MOTIVATION AND OBJECTIVES

5-stage configuration of the axial turbine test rig at the Institute of Turbomachinery and Fluid Dynamics

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.

RESULTS

Using aero engine turbine guide vanes, it could be shown that regeneration-related deviations from the original geometry have a significant influence on the aerodynamic vibration excitation of the downstream blade rows. A change in the stagger angle, for example, has a significant influence on the vibration excitation of the downstream blades. The resulting oscillation amplitudes quadruple compared to the original cascade.

Example of blade wear: burn-off at blade leading edges, source of thermal streaks

CURRENT RESEARCH AND OUTLOOK

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.


PUBLICATIONS

  • Hauptmann, T.; Aschenbruck, J.; Seume, J. R. (2017) Forced Response Excitation due to Stagger Angle Variation in a Multi-Stage Axial TurbineInternational Journal of Gas Turbine, Propulsion and Power Systems Volume 9 (Number 3), 1--11
  • Aschenbruck, J.; Seume, J. R. (2015) Experimentally Verified Study of Regeneration-Induced Forced Response in Axial TurbinesJournal of Turbomachinery 137 (3), S. 1–10
    DOI: 10.1115/1.4028350
All publications of the Collaborative Research Centre

SUBPROJECT LEADER

Prof. Dr.-Ing. Jörg Seume
Address
Appelstraße 9
30167 Hannover
Address
Appelstraße 9
30167 Hannover

STAFF

Dipl.-Ing. Dominic Schmolke
Address
Appelstraße 9
30167 Hannover
Building
Room
004
Address
Appelstraße 9
30167 Hannover
Building
Room
004