Brush seals are used in turbomachinery for reduced leakage as compared to conventional seals such as labyrinth seals. Early applications tended to favor having a line-to-line to a slight interference fit of the bristles to the shaft, but more recent applications have favored the use of a slight initial clearance fit for the purpose of reducing bristle wear. In these brush seals with clearance, the phenomenon of bristle blow-down largely negates the 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 then compared to a calibrated brush seal leakage model.
Tolerances in brush installation may lead to a brush seal bore that is eccentric to the rotor. The influence of this seal eccentricity on measured leakage performance is also characterized in the paper. Seal eccentricities up to 55% of brush fence height are tested. Effective clearances for eccentric operation are estimated from the measurements.
Brush seals are described as unidirectional seals because the bristles have 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.