Abstract
Brush seals operate within harsh environments within rotating machinery. They are typically exposed to high pressures and temperatures, rotor-stator relative movements, and high shaft rotational speeds leading to highly swirling inlet flow. The compliant nature of the bristle elements makes them susceptible to flow-induced vibrations, particularly associated with high levels of inlet swirl velocity. This can lead to fatigue fracture of the bristles and may also impact seal leakage. This paper establishes a two-way fluid-structure interaction (FSI) method that combines a three-dimensional transient flow model of brush seals with an analytical mechanical model of bristle deflections. This method can quickly obtain the flow field characteristics and bristle deflection of brush seals with satisfactory accuracy. Based on this method, bristle deflections under typical aerodynamic loads in operation, up to 0.4MPa differential pressure and 200m/s inlet swirl velocity, were investigated to understand bristle response under steady-state and transient conditions. This study shows, for the first time, that under the influence of inlet swirl, and particularly at inlet swirl velocities of 200m/s where bristle slip is known to occur for similar pack geometries, the upstream row of bristles exhibits a circumferential displacement oscillation due to interaction between the swirling flow and bristle structure. This occurs with a characteristic frequency of 441Hz which is of the order of the bristle natural frequency. Results indicate that a consistent oscillation amplitude is established over the simulation timescales, suggesting a typical forced vibration response.
