Abstract
When subject to highly swirling inlet flow, the bristles on the upstream face of a brush seal in gas turbine engines tend to slip circumferentially, which may lead to aeromechanical instability and seal failure. In this article, a new design of the front plate of brush seal, which mitigates this effect, is presented. Angled ribs on the upstream side of the front plate are used to reduce the swirl of the flow impacting on the bristle pack. The effects of the rib geometry, including angle of inclination and height-to-spacing ratio, are investigated using computational fluid dynamics, and a bulk porous medium model of the bristle pack, on a simple seal geometry. Results show that the ribs can effectively regulate the flow upstream of the bristle pack, reducing the swirl and channeling flow radially inward to the sealing section, resulting in decreased circumferential forces on the bristles. Ribs inclined at 20° to the radial direction and with height-to-spacing ratio of 0.4 were selected as the most effective of those investigated for the seal geometry under study. A model of an aeroengine preswirled cooling air chamber was created to give insight into the inlet swirl boundary conditions that a preswirl seal brush seal could be subjected to at a range of leakage flow rates and inlet swirl velocities. The new design and upstream roughness feature substantially reduced inlet swirl velocity incident on the bristle pack. The findings in this work could have a significant impact on brush seal design and, in particular, mitigate a significant operational risk of swirl-induced instability in high-pressure, high-speed shaft seal locations.
Highlights
Brush seals are used for sealing between rotating and stationary components in applications with high-speed rotating shafts such as aeroengines
The most effective rib design from the parametric study is adopted, and the seal has a 0.2-mm clearance between the bristle pack and the rotor
The circumferential aerodynamic forces loading on the bristles, which scale with swirl dynamic head, will be reduced by a factor of approximately 250
Summary
Brush seals are used for sealing between rotating and stationary components in applications with high-speed rotating shafts such as aeroengines. As reported by Chupp et al (2002), compared to traditional labyrinth seals (Asok et al, 2008), brush seals improve sealing performance by reducing the leakage rate to 10% to 20% that of the latter. Other performance factors such as wear, stability, and in-service deterioration have, to date, limited the application of brush seals (Aslanzada et al, 2009). Further research and development are needed to understand and improve these aspects so that brush seals can achieve their full potential. In order to reduce the wear between the bristles and the rotor and make it easier for the bristles to adapt to the radial movement of the rotor, the bristles are typically inclined at 30°–60° (φ) to the radial
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