Vibrations of structures with cyclic symmetry: Application to the case of turbine engines
Abstract
A great number of gas turbine components gives cyclic symmetry properties which may be useful to analyze such parts. The resonance occurrences are numerous because of the different harmonics of the rotational speed. Shift phase characteristics between each periodic sector can be easily used to represent the complex system forces made of air flow distortions for instance. The aerodynamical forces are transmitted to the structure mainly by the blades. From this point, we note under some stationary pressure deviations, fixed in the space reference, that the airfoil undergoes pressure fluctuations during its revolution cycle. This stationary phenomena is periodic in the blade reference. It shows a forward or backward wave propagation whose frequency is determined within each frame. A couple of eigen modes, except under some particular conditions, can be found using cyclic symmetry conditions at exactly the same eigen value. The linear combination of both modes are used to analyze the wave propagation. Resonance conditions are shown in this paper and an assessment of an excitability factor has been introduced to reckon the potentially dangerous modes. This method is applied on a modal analysis of an impeller of a gas turbine engine designed by TURBOMECA. This step is prerequisite to a complete simulation of dynamic responses incorporating dissipative functions and the aeroelastic coupling which mainly governs such a vibration phenomena.
 Publication:

In AGARD
 Pub Date:
 March 1994
 Bibcode:
 1994trsg.agar.....M
 Keywords:

 Aeroelasticity;
 Air Flow;
 Airfoils;
 Backward Waves;
 Dynamic Response;
 Engine Parts;
 Gas Turbine Engines;
 Impellers;
 Pressure Oscillations;
 Structural Vibration;
 Symmetry;
 Turbine Engines;
 Wave Propagation;
 Complex Systems;
 Dissipation;
 Harmonics;
 Resonance;
 Simulation;
 Structural Mechanics