Numerical Simulation of Three-Dimensional Bristle Bending in Brush Seals

Abstract

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.

Theoretical Analysis of Brush Seals Leakage Using Local Computational Fluid Dynamics Estimated Permeability Laws

“…The calculation of the bristles pack deformations is based on the method described by Guardino and Chew in 2005 [10]. Each bristle of the pack is modeled using the linear beam theory and is submitted to four different efforts:…”

Experimental Analysis of Small Diameter Brush Seals and Comparisons With Theoretical Predictions

“…Another category of more recent theoretical models considers the brush as a porous medium [5][6][7][8][9][10]. These methods can be considered as extensions of the approach used by Chupp et al [2,3].…”

“…The model is similar to the approach used in Ref. [9]and is based on an iterative fluid-structure interaction between the bristles modeled as elastic bodies and the brush flow calculated from a CFD approach. The model was validated by comparing the estimated torque with experimental data but flow rates were not reported.…”

“…Recently, the present authors have introduced a similar model that assimilates the brush with a porous, deformable medium [14]. As in the model of Guardino and Chew [9], the bristles deform under the effect of pressure forces, due to the interference with the rotor and due to the contact with the back plate. It results a porous medium with spatially varying porosity.…”

“…The model was validated by comparisons with the experimental data of Bailey and Long [16], which were the only one in the literature containing the details that the model needed. Other researchers used the same experimental results for validating brush seals theoretical models [9], because it documents well the geometric characteristics of the brush.…”