Aerodynamic damping predictions in turbomachines using a coupled fluid-structure model

Flow-induced vibration of turbomachine blade rows is a coupled fluid-structure problem. Thus, rather than separate fluid and structural models, a coupled interacting fluid-structures analysis is needed. This need is addressed by extending the finite element code ALE3D that solves the three-dimensional Euler equations to model the unsteady aerodynamics of turbomachine blade rows. The same finite element model is applied to both the blading And the fluid, which results in consistency between the fluid and structure. Such a coupled interacting fluid-structure analysis enables the aerodynamic damping of multiple vibration modes to be predicted from two time-domain simulations: one with the blading in a vacuum and one with the blading in flow. This novel approach to predict aerodynamic damping is demonstrated by the consideration of a modern transonic compressor blade row. The blading is first impulsed in its first bending and first torsion modes in a vacuum. It is then immersed in the design-point flowfield and impulsed in its first bending and first torsion modes again. Signal processing tools applied to the predicted blade response time history extract the difference in the decay rate of both modes.