The InterBristle Pressure Field in a LargeScale Brush Seal

Abstract

Brush seals promise improvements to the widely used labyrinth seal in regulating turbomachinery leakages. Enhanced resistance to the flow is provided by a static ring of densely packed fine wire bristles that are angled in the direction of rotation and flex to accommodate rotor excursions. A largescale brush seal was constructed to study the leakage characteristics in direct relation to the pressure field within and surrounding the bristle pack for multiple clearance conditions, therefore developing the understanding of brush seal fluid dynamic behavior. The governing parameter controlling leakage behavior transitioned from pressure ratio for a large clearance, to pressure load for a lineonline configuration. In all cases, leakage flow converged to an asymptotic value once maximum levels of bristle blowdown and pack compaction were attained. For both clearance configurations, this occurred at a pressure ratio corresponding to that at which axial distributions of pressure converged; equivalent behavior was noted for the lineonline configuration with pressure drop. Comparatively small changes were experienced in leakage behavior and in the interbristle pressure field with increasing pressure drop for the lineonline brush seal. This indicated that brush seal performance is more influenced by changes in bristle blowdown than bristle pack compaction.