| The fluid-structure interaction problems associated with turbine engine applications are tackled by means of a time marching method. It is well known that both fluid and structural characteristics are playing an important role, and neglecting one of these characteristics leads to an unrealistic simplification of the problem. The purpose of this study is to show that the fluid and structure characteristics need to be considered with their fully coupled interaction, in order to capture the true vibrations features of the system. The method developed here addresses all the aspects of the problem, starting with the modeling of the flow propagated disturbances and ending with the estimation of the fatigue life of the blades. The choice of a time marching algorithm enables the consideration of the various interference aspects characteristics to the jet engine environment, and allows a modular approach in which the components may be substituted with other more accurate or efficient procedures. The coupling between fluid and structure is achieved by an iterative process that ensures the proper transfer of information between the aerodynamics and structural modules.; The methodology has been validated by comparison with reference linear theory data for a flutter case. However, the present results have indicated that nonlinear effects become more important at speeds close to the flutter point. Modeling of flow disturbances encountered in turbomachinery is realized by means of periodic patterns of discrete vortices, which enable a sufficiently accurate representation of the physical phenomenon. The results show that the fluid-structure coupling leads, for all the external excitation cases considered, to a Limit Cycle Oscillation (LCO) behavior. Other important findings are related to resonance phenomena. It is shown that (structural) resonance can lead to dramatic reductions (up to ten orders of magnitude) in the blade fatigue life. An aerodynamic resonance phenomenon is identified and investigated, that can lead to a large increase in the aerodynamic response of the blade subjected to a periodic vortex pattern, when the chord of the blade equals half of the wavelength of the excitation. |
