Controlled gap seal with surface discontinuities

A gas turbine engine, comprising:

• a controlled gap seal located between a housing and a shaft of the gas turbine engine, the shaft rotating about a central axis of the gas turbine engine, the controlled gap seal including:
• a ring in a sealing engagement with the housing, the ring annularly and continuously extending about the central axis;
• a runner secured to the shaft and rotatable relative to the ring, the runner having a runner face facing a ring face of the ring, the ring face spaced apart from the runner face by a gap;
• and
• a plurality of surface discontinuities circumferentially distributed around the central axis located on the runner face, a face of the ring that faces the runner, and/or a face of the housing facing the runner, a distance taken between a first set of two adjacent ones of the surface discontinuities being different than that between a second set of two adjacent ones of the surface discontinuities.

A method of operating a controlled gap seal, comprising:

• imparting a pressure differential between a cavity and an environment outside the cavity;
• fluidly connecting the cavity to the environment via a gap of the controlled gap seal, the gap located between a rotating component and a static component of the controlled gap seal;
• and
• disrupting a flow circulating within the gap by circulating the flow between surface discontinuities circumferentially distributed around a central axis of the controlled gap seal, the surface discontinuities located on the rotating component and/or the static component, a first set of adjacent surface discontinuities are circumferentially spaced from each other at a different distance than a second set of adjacent surface discontinuities.