Numerical Investigation of Labyrinth Seal Aeroelastic Stability

Labyrinth seals, used to prevent flow leakage between rotating and stationary components in aero engines, may be prone to aeroelastic instabilities. Current work investigates the aeroelastic stability of flexible seals using a coupled fluid-structure code. The aim is to determine the key parameters and to explain the flutter mechanism with a view to establish simple design rules. The unsteady flow field due to seal vibration is solved in a time accurate manner to determine the aerodynamic damping of the seal. The fluid model is based on non-linear time-accurate unsteady Reynolds-averaged Navier-Stokes equations. The vibrating structure is modelled using a classical modal approach. The parameters investigated are the influence of the seal natural frequencies and the support position for the seal. The geometry considered is a multi-finned straight-through seal. A ten-degree sector is meshed for the simulations, and cyclic symmetry boundary conditions are used. The stability is found to be affected by both the mechanical/acoustic frequency ratio and the support side of the seal. The aerodynamic work depends mainly on the cavity shape, the mode shape and the unsteady pressure phase distribution. It is found that the phase variation from one cavity to another is of primary importance to assess the relative contribution of each cavity to the aerodynamic work. The results agree qualitatively with those available in the literature.