Analysis of Deformation, Blow-Out Mechanism, and Leakage Behavior of Brush Seals Under Distributed Pressure Loading

Brush seals using compliant bristle packs can reduce turbomachinery leakage more effectively than conventional labyrinth seals, but their coupled structural and flow behavior makes design difficult. Under large pressure loading, bristles can deflect, lose contact with the rotor, and generate clearance, causing the sharp leakage increase known as blow-out. This study develops a model linking nonlinear bristle deflection, rotor–bristle contact loss, and leakage response. The bristle is treated as an inextensible nonlinear elastic member subjected to distributed pressure loading, backing-plate support, and frictional rotor contact. Contact and separated states are solved iteratively using boundary-value and initial-value solvers. Leakage through the bristle pack is calculated using a random bristle-bed formulation, and leakage through generated clearance is evaluated with an orifice-flow model. The model agrees well with published bristle-deflection predictions. Increasing pressure load reduces normal contact force until lift-off occurs, producing clearance and a sharp rise in leakage. Increasing front-plate free height shifted lift-off from pressure ratio ≈4 to ≈2, while clearance flow contributed up to 36.5% after lift-off. Brush-seal blowout is therefore governed by the transition from rotor–bristle contact to separation. Lower back-plate height can delay blow-out, but hysteresis and durability tradeoffs must be considered.