Investigation of Grooved Front Plate for Inlet Swirl Reduction in Brush Seals

Abstract

Brush seals are plausible replacements for conventional labyrinth seals in gas turbine internal air systems. They can offer superior leakage performance due to their compliant nature and reduced effective clearance during operation. However, highly swirling flow and aerodynamic forces on the upstream bristles could lead to bristle back aero-elastic instability at high-shaft speed locations. Previous research has shown that the bristles in an idealized pack are displaced from their equilibrium position at swirl velocities of 150 m.s−1 and above for a bristle diameter of 0.1 mm. This study investigates grooves as a means of improving brush seal robustness in these locations by reducing inlet swirl incident on the bristle pack. A parametric study of a simple groove geometry was conducted using computational fluid dynamics (CFD) and a porous medium representation of the bristle pack to achieve representative seal leakages. Groove length, width, angle, and pitch were identified as important parameters for swirl reduction. The performance of ribs from previous research can be replicated and improved upon. A design of experiments (DOE) approach was implemented to investigate a novel groove design geometry. Combining a horizontal channel with an inclined groove enables a higher spacing to achieve the same swirl reduction due to drag and flow channeling/mixing effects at the inner radius. The resulting trends indicate that the novel design performs as intended for the selected boundary conditions in substantially reducing inlet swirl, thus helping to mitigate the above risk of premature seal deterioration and failure.