Measured Influence of Clearance and Eccentricity on Brush Seal Leakage Characteristics

Brush seals are known to offer sealing advantage as compared to conventional seals such as labyrinth seals. Brush seals operating with initial radial clearance have the advantage of reduced bristle wear as compared to brush seals with line-to-line or interference fit.  In brush seals with clearance, the phenomenon of bristle blow-down can negate the possible leakage degradation due to clearance, with bristles bending to reduce the clearance gap. This paper presents experimental results for a 10.5 inch bore brush seal with 0.0028 inch bristle diameter. Bristle blow-down is characterized with measurements at three different clearances and comparison with a calibrated brush seal leakage model.

Tolerances in brush installation, may lead to brush seal bore which is not concentric with the rotor. The influence of this seal eccentricity on measured leakage performance is also characterized. Seal eccentricities up to 62% of brush fence height are tested. Effective clearances for eccentric operation are estimated from the measurements.

Brush seals are described as unidirectional seals due to bristles aligned with a lay angle in the direction of rotation. This paper also investigates the influence of rotation direction on measured leakage performance of brush seal. This influence is characterized by non-pressurized reverse rotation operation and measurement of leakage performance prior to and after reverse rotation operation.