A previous paper described measurements of damping and leakage of a brush hybrid seal in a nonrotating test apparatus. In those experiments most of the damping came from the brush. This paper describes further experiments with this seal in a rotordynamic rig designed to determine if the bristles will still contribute significant damping at large amplitudes after wearing in to a line-line contact. These tests continued to show much more damping and much less leakage than a labyrinth seal of the same dimensions. The damping performance is even better after the brush is worn in. In the rotating experiments it was discovered that the brush elements also produce a surprising amount of friction torque and consequent power loss, especially at high pressure drops. During the experiments it was found that the brush friction is destabilizing to backward whirl, and that support asymmetry suppresses the instability.

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