Vortex Induced Flutter in Compliant Plate Seals

This paper investigates the possibility of vortex induced flutter in GE compliant plate seals (CPS). The CPS consists of a ring of slotted compliant plates attached circumferentially around the rotor, with an intermediate plate seated in the slot. Experiments show that the compliant plates vibrate in the flow field with amplitude that is a function of the differential pressure applied across the seal. The vibrations are caused by potentially multiple flow induced vibration mechanisms operating during different flow regimes. This work focuses on the dynamic instabilities that may be caused by the vortices shed by individual compliant plates and the intermediate plate. We model the compliant plate seal as a ring of a large number of locally coupled oscillators, with nonlinear stiffness arising from hydrostatic feedback. A two-way coupling exists between the structural and wake dynamics, leading to the phenomenon of “lock-in” between the wake and successive modes of seal vibration as the flow velocity is increased. Using eigenvalue analysis, we obtain the transition boundaries that divide the parameter space into sets of regions with positive and negative damping, corresponding to boundaries of onset and end of vortex induced flutter. Based on averaged equations, the amplitude of the limit cycles of the structure and wake dynamics and the phase between them is determined. It is found that the nonlinearities in seal stiffness and the nature of coupling between the compliant plates have a significant effect on the stability boundaries.