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This paper presents a new method for predicting the 3D bending behaviour of bristles in brush seals. The model builds upon and addresses shortcomings in an earlier 2D bending model. The work was motivated by the need to develop a general 3D solid mechanical model which can ultimately be incorporated into CFD models of flow and heat transfer through brush seals. The iterative method considered here, which is based upon linear beam-bending theory, allows relatively large numbers of bristles to be considered with arbitrary imposed aerodynamic forces. Bristle-to-bristle contacts and deflections are considered, as well as shaft and backing ring contacts. The method also allows arbitrary initial bristle packs and lay-angles to be considered, as well as periodic conditions so that the model represents a sector of a brush seal. Other physically important features such as the so-called ‘3D-splay’ and ‘inclined prop’ effects are also taken into account. The method described here has been incorporated into a new computer code called ‘SUBSIS’ (Surrey University Brush Seal Iterative Simulator). Example results from this code are presented which show the bending behaviour of initially hexagonally packed brush seals under model imposed pressure loads acting on the bristle tips. The effects of rotor incursions into the bristle pack, increase of the pressure load, and changes in the lay-angle and Young’s modulus are also shown. The results illustrate the expected bending behaviour observed in real brush seals. Procedures for coupling SUBSIS with CFD models are also currently under investigation.

This paper presents a new method for predicting the three-dimensional (3D) bending behavior of bristles in brush seals. The model builds on and addresses shortcomings in an earlier two-dimensional bending model. The work was motivated by the need to develop a general 3D solid mechanical model that can ultimately be incorporated into CFD models of flow and heat transfer through brush seals. The iterative method considered here, which is based on linear beam-bending theory, allows relatively large numbers of bristles to be considered with arbitrary imposed aerodynamic forces. Bristle-to-bristle contacts and deflections are considered, as well as shaft and backing ring contacts. The method also allows arbitrary initial bristle packs and lay-angles to be considered, as well as periodic conditions so that the model represents a sector of a brush seal. Other physically important features, such as the so-called 3D-splay and inclined prop effects, are also taken into account. The method described here has been incorporated into a new computer code called SUBSIS (Surrey University Brush Seal Iterative Simulator). Example results from this code are presented that show the bending behavior of initially hexagonally packed brush seals under model imposed pressure loads acting on the bristle tips. The effects of rotor incursions into the bristle pack, increase of the pressure load, and changes in the lay-angle and Young’s modulus are also shown. The results illustrate the expected bending behavior observed in real brush seals. Procedures for coupling SUBSIS with CFD models are also currently under investigation.

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D roughness patterns on the stationary wall. A ‘unit-based’ approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various two-dimensional or three-dimensional roughness patterns on the stationary wall. A “unit-based” approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.