Patent ID: 8439630

Claim:
A monitoring system for a gas turbine engine, the monitoring system comprising: a viewing tube assembly having an exterior surface and an interior surface, and an inner end and an outer end, the inner end located adjacent to a hot gas flow path within the gas turbine engine and the outer end located adjacent to an outer casing of the gas turbine engine; wherein the viewing tube assembly comprises a lens tube and a lens housing located within the lens tube at the inner end of the viewing tube assembly; an aperture wall located at the inner end of the viewing tube assembly, the aperture wall extending radially inwardly relative to the interior surface of the viewing tube assembly at the inner end thereof; an optical element located within the viewing tube assembly adjacent to the inner end and spaced from the aperture wall to define a cooling and purge chamber therebetween; an aperture defined in the aperture wall for passage of light from the hot gas flow path to the optical element, the aperture having a diameter smaller than a diameter of the optical element; a flange extending radially inwardly from an inner surface of the lens tube at the inner end, the flange including a opening for passage of light from the hot gas flow path, the opening having a diameter smaller than the diameter of the optical element; the flange being spaced axially from the aperture wall on a side of the aperture wall opposite from the chamber to defined an annular area therebetween, the annular area surrounding the aperture and extending radially outwardly from the opening in the flange; one or more swirl passages defined in the lens housing between the aperture wall and the optical element for passage of cooling air from a location outside the viewing tube assembly into the chamber and supplied from a first source of cooling air, wherein the one or more swirl passages effect a swirling movement of air in a circumferential direction within the chamber; and one or more openings defined through the lens tube between the aperture wall and the flange for passage of air from a second source of cooling air into the annular area between the aperture wall and the flange.