Using Layered Variable-Diameter Bristle Pack to Improve the Bristle Deflection, Bending Stress, and Reaction Tip Force Performance of Brush Seals

Abstract

Abstract. The excessive bristle deflection and high bristle stress level at contact region in high pressure differential environment results in overload related brush seal failures. Variable bristle diameter (VBD) brush seals overcome those serious issues by applying a sandwich structure of layered different-diameter bristles. A realistic aerodynamic force distribution on the bristle pack extracted from computational fluid dynamics (CFD) using the three-dimensional Reynolds-averaged Navier–Stokes solution is adopted to calculate bristle bending and mechanical contacts. The shear force and bending moment diagrams along the bristle length give improved understanding of the bristle bending characteristics and deflection magnitudes. The bristle deflection and stress profile obtained from correlated finite element analysis (FEA) provide an insight into VBD brush seal behavior coupled with both aerodynamic and mechanical loads. The results show that replacing thin bristles with thick ones weakens the sealing performance of brush seals, especially in the rear region of bristle pack. The axial bristle deflection increases with pressure loads and decreases in subsequent downstream rows due to the closure of axial spacing. Bristle blow down close the clearance between the bristle tip and rotor due to axial bristle deflection by means of radial and circumferential bristle deflection. Significantly reduced axial bristle deflection, stress level, and reaction tip force of the bristle pack can be realized by using the thick bristles in the rear region, which featured with large moment of inertia.