Combined 3D Fluid Dynamics and Mechanical Modelling of Brush Seals

Development and application of a combined 3D computational fluid dynamics (CFD) and 3D bristle bending model for brush seals is described. The CFD model is created using commercial CFD mesh generation and solver software. A small gap is assumed between all bristles in the CFD model so as to avoid meshing problems at contact points and allow for imperfections in bristle geometry. The mechanical model is based on linear beam bending theory and allows large numbers of bristles to be modelled with arbitrary bristle-to-bristle contact and bristle to backing ring and shaft contact. Aerodynamic forces on the bristles are imported from the CFD solution. Deformed geometries may be exported directly to the mesh generation software, allowing iterative solution of the coupled aerodynamic/mechanical problem. Results from the model are presented for representative brush seal geometry. It is shown that even with initially circumferentially symmetric bristle packing and aerodynamic forces, bristle deflections tend to lead to asymmetric packing. This currently limits application of the fully coupled model, but use of the combined (but not fully coupled) model is nevertheless considered to give a powerful analysis tool. Shaft torque predictions are found to be in good agreement with measurements, and the effect of swirl in the inlet flow has been examined.